1
|
Li YY, Boeraeve M, Cho YH, Jacquemyn H, Lee YI. Mycorrhizal Switching and the Role of Fungal Abundance in Seed Germination in a Fully Mycoheterotrophic Orchid, Gastrodia confusoides. Front Plant Sci 2022; 12:775290. [PMID: 35095954 PMCID: PMC8792533 DOI: 10.3389/fpls.2021.775290] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Accepted: 12/17/2021] [Indexed: 06/14/2023]
Abstract
Mycorrhizal associations are essential for orchid germination and seedling establishment, and thus may constrain the distribution and abundance of orchids under natural conditions. Previous studies have shown that germination and seedling establishment in several orchids often decline with increasing distance from adult plants, resulting in non-random spatial patterns of seedling establishment. In contrast, individuals of the fully mycoheterotrophic orchid Gastrodia confusoides often tend to have random aboveground spatial patterns of distribution within bamboo forests. Since G. confusoides is parasitic on litter-decaying fungi, its random spatial patterns of distribution may be due to highly scattered patterns of litter-decaying fungi within bamboo forests. To test this hypothesis, we first identified the main mycorrhizal fungi associating with developing seeds and adult plants at a bamboo forest site in Taiwan using Miseq high-throughput DNA sequencing. Next, we combined seed germination experiments with quantitative PCR (qPCR) analyses to investigate to what extent the abundance of mycorrhizal fungi affected spatial patterns of seed germination. Our results show that seed germination and subsequent growth to an adult stage in G. confusoides required a distinct switch in mycorrhizal partners, in which protocorms associated with a single Mycena OTU, while adults mainly associated with an OTU from the genus Gymnopus. A strong, positive relationship was observed between germination and Mycena abundance in the litter, but not between germination and Gymnopus abundance. Fungal abundance was not significantly related to the distance from the adult plants, and consequently germination was also not significantly related to the distance from adult plants. Our results provide the first evidence that the abundance of litter-decaying fungi varies randomly within the bamboo forest and independently from G. confusoides adults.
Collapse
Affiliation(s)
- Yuan-Yuan Li
- Beijing Key Laboratory of Seed Disease Testing and Control, College of Plant Protection, China Agricultural University, Beijing, China
| | - Margaux Boeraeve
- Department of Biology, Plant Conservation and Population Biology, KU Leuven, Leuven, Belgium
| | - Yu-Hsiu Cho
- Biology Department, National Museum of Natural Science, Taichung, Taiwan
| | - Hans Jacquemyn
- Department of Biology, Plant Conservation and Population Biology, KU Leuven, Leuven, Belgium
| | - Yung-I Lee
- Department of Life Science, National Taiwan University, Taipei, Taiwan
| |
Collapse
|
2
|
Abstract
When a phenological shift affects a demographic vital rate such as survival or reproduction, the altered vital rate may or may not have population-level consequences. We review the evidence that climate change affects populations by shifting species’ phenologies, emphasizing the importance of demographic life-history theory. We find many examples of phenological shifts having both positive and negative consequences for vital rates. Yet, few studies link phenological shifts to changes in vital rates known to drive population dynamics, especially in plants. When this link is made, results are largely consistent with life-history theory: Phenological shifts have population-level consequences when they affect survival in longer-lived organisms and reproduction in shorter-lived organisms. However, there are just as many cases in which demographic mechanisms buffer population growth from phenologically induced changes in vital rates. We provide recommendations for future research aiming to understand the complex relationships among climate, phenology, and demography, which will help to elucidate the extent to which phenological shifts actually alter population persistence.
Collapse
Affiliation(s)
- Amy M. Iler
- Negaunee Institute for Plant Science Conservation and Action, Chicago Botanic Garden, Glencoe, Illinois 60022, USA
| | - Paul J. CaraDonna
- Negaunee Institute for Plant Science Conservation and Action, Chicago Botanic Garden, Glencoe, Illinois 60022, USA
| | | | - Eric Post
- Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, California 95616, USA
| |
Collapse
|
3
|
Berry EJ, Cleavitt NL. Population dynamics and comparative demographics in sympatric populations of the round‐leaved orchids
Platanthera macrophylla
and
P. orbiculata. POPUL ECOL 2021. [DOI: 10.1002/1438-390x.12092] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Eric J. Berry
- Biology Department St. Anselm College Manchester New Hampshire USA
| | - Natalie L. Cleavitt
- Department of Natural Resources and the Environment, Fernow Hall Cornell University Ithaca New York USA
| |
Collapse
|
4
|
Ladouceur E, Stanley Harpole W, Blowes SA, Roscher C, Auge H, Seabloom EW, Chase JM. Reducing dispersal limitation via seed addition increases species richness but not above-ground biomass. Ecol Lett 2020; 23:1442-1450. [PMID: 32567139 DOI: 10.1111/ele.13566] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Revised: 04/17/2020] [Accepted: 05/18/2020] [Indexed: 01/20/2023]
Abstract
Seed dispersal limitation, which can be exacerbated by a number of anthropogenic causes, can result in local communities having fewer species than they might potentially support, representing a potential diversity deficit. The link between processes that shape natural variation in diversity, such as dispersal limitation, and the consequent effects on productivity is less well known. Here, we synthesised data from 12 seed addition experiments in grassland communities to examine the influence of reducing seed dispersal limitation (from 1 to 60 species added across experiments) on species richness and productivity. For every 10 species of seed added, we found that species richness increased by about two species. However, the increase in species richness by overcoming seed limitation did not lead to a concomitant increase in above-ground biomass production. This highlights the need to consider the relationship between biodiversity and ecosystem functioning in a pluralistic way that considers both the processes that shape diversity and productivity simultaneously in naturally assembled communities.
Collapse
Affiliation(s)
- Emma Ladouceur
- German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena, Deutscher Platz 5e, Leipzig, 04103, Germany.,Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle (Saale), 06120, Germany.,Department of Physiological Diversity, Helmholtz Centre for Environmental Research -UFZ, Permoserstrasse 15, Leipzig, 04318, Germany
| | - W Stanley Harpole
- German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena, Deutscher Platz 5e, Leipzig, 04103, Germany.,Department of Physiological Diversity, Helmholtz Centre for Environmental Research -UFZ, Permoserstrasse 15, Leipzig, 04318, Germany.,Institute of Biology, Martin Luther University Halle-Wittenberg, Am Kirchtor 1, Halle (Saale, 06108, Germany
| | - Shane A Blowes
- German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena, Deutscher Platz 5e, Leipzig, 04103, Germany.,Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle (Saale), 06120, Germany
| | - Christiane Roscher
- German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena, Deutscher Platz 5e, Leipzig, 04103, Germany.,Department of Physiological Diversity, Helmholtz Centre for Environmental Research -UFZ, Permoserstrasse 15, Leipzig, 04318, Germany
| | - Harald Auge
- German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena, Deutscher Platz 5e, Leipzig, 04103, Germany.,Department of Community Ecology, Helmholtz Centre for Environmental Research -UFZ, Theodor-Lieser-Straße 4, Halle (Saale), 06120, Germany
| | - Eric W Seabloom
- Department of Ecology Evolution & Behavior, University of Minnesota, St. Paul, Minnesota, 55108, USA
| | - Jonathan M Chase
- German Centre for Integrative Biodiversity Research (iDiv) Leipzig-Halle-Jena, Deutscher Platz 5e, Leipzig, 04103, Germany.,Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle (Saale), 06120, Germany
| |
Collapse
|
5
|
Rand TA, West NM, Russell FL, Louda SM. Post-dispersal factors influence recruitment patterns but do not override the importance of seed limitation in populations of a native thistle. Oecologia 2020; 193:143-53. [PMID: 32322985 DOI: 10.1007/s00442-020-04656-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 04/11/2020] [Indexed: 10/24/2022]
Abstract
Whether plant populations are limited by seed or microsite availability is a long-standing debate. However, since both can be important, increasing emphasis is placed on disentangling their relative importance and how they vary through space and time. Although uncommon, seed addition studies that include multiple levels of seed augmentation, and follow plants through to the adult stage, are critical to achieving this goal. Such data are also vital to understanding when biotic pressures, such as herbivory, influence plant abundance. In this study, we experimentally added seeds of a native thistle, Cirsium canescens, at four augmentation densities to plots at two long-term study sites and quantified densities of seedlings and reproductive adults over 9 years. Recruitment to both seedling and adult stages was strongly seed-limited at both sites; however, the relative strength of seed limitation decreased with plant age. Fitting alternative recruitment functions to our data indicated that post-dispersal mortality factors were important as well. Strong density-dependent mortality limited recruitment at one site, while density-independent limitation predominated at the other. Overall, our experimental seed addition demonstrates that the environment at these sites remains suitable for C. canescens survival to reproduction and that seed availability limits adult densities. The results thus provide support for the hypothesis that seed losses due to the invasive weevil, Rhinocyllus conicus, rather than shifting microsite conditions, are driving C. canescens population declines. Shifts in the importance of density-dependent recruitment limitation between sites highlights that alternate strategies may be necessary to recover plant populations at different locations.
Collapse
|
6
|
Maron JL, Hajek KL, Hahn PG, Pearson DE. Seedling recruitment correlates with seed input across seed sizes: implications for coexistence. Ecology 2019; 100:e02848. [PMID: 31351014 DOI: 10.1002/ecy.2848] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 07/11/2019] [Accepted: 07/15/2019] [Indexed: 11/09/2022]
Abstract
Understanding controls on recruitment is critical to predicting community assembly, diversity, and coexistence. Theory posits that at mean fecundity, recruitment of highly fecund small-seeded plants should be primarily microsite limited, which is indicated by a saturating recruitment function. In contrast, species that produce fewer large seeds are more likely to be seed-limited, which is characterized by a linear recruitment function. If these patterns hold in nature, seed predation that disproportionately affects larger-seeded species can limit their establishment. We tested these predictions by comparing recruitment functions among 16 co-occurring perennial forb species that vary by over two orders of magnitude in seed size. We also assessed how postdispersal seed predation by mice influenced recruitment. We added seeds at densities from zero to three times natural fecundity of each species to undisturbed plots and examined spatial variation in recruitment by conducting experiments across 10 grassland sites that varied in productivity and resource availability. Consistent across two replicated years, most species had linear recruitment functions across the range of added seed densities, indicative of seed-limited recruitment. Depending on year, the recruitment functions of only 19-37% of target species saturated near their average fecundity, and this was not associated with seed size. Recruitment was strongly inhibited by rodent seed predation for large-seeded species but not for smaller-seeded species. Proportional recruitment was more sensitive to spatial variation in recruitment conditions across sites for some small-seeded species than for large-seeded species. These results contradict the common belief that highly fecund small-seeded species suffer from microsite-limited recruitment. Rather, they imply that, at least episodically, recruitment can be strongly correlated to plant fecundity. However, proportional recruitment of small-seeded species was inhibited at productive sites to a greater extent than large-seeded species. Results also show that in a system where the dominant granivore prefers larger seeds, low-fecundity large-seeded species can suffer from even greater seed-limited recruitment than would occur in the absence of predators.
Collapse
Affiliation(s)
- John L Maron
- Division of Biological Sciences, University of Montana, Missoula, Montana, 59812, USA
| | - Karyn L Hajek
- Division of Biological Sciences, University of Montana, Missoula, Montana, 59812, USA
| | - Philip G Hahn
- Division of Biological Sciences, University of Montana, Missoula, Montana, 59812, USA
| | - Dean E Pearson
- Division of Biological Sciences, University of Montana, Missoula, Montana, 59812, USA.,Rocky Mountain Research Station, U.S. Department of Agriculture Forest Service, Missoula, Montana, 59801, USA
| |
Collapse
|
7
|
Hovick SM, Whitney KD. Propagule pressure and genetic diversity enhance colonization by a ruderal species: a multi‐generation field experiment. ECOL MONOGR 2019. [DOI: 10.1002/ecm.1368] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Stephen M. Hovick
- Department of Evolution, Ecology, and Organismal Biology The Ohio State University Columbus Ohio 43210 USA
| | - Kenneth D. Whitney
- Department of Biology University of New Mexico Albuquerque New Mexico 87131 USA
| |
Collapse
|
8
|
Belinchón R, Harrison PJ, Mair L, Várkonyi G, Snäll T. Local epiphyte establishment and future metapopulation dynamics in landscapes with different spatiotemporal properties. Ecology 2016; 98:741-750. [PMID: 27984632 DOI: 10.1002/ecy.1686] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Revised: 11/16/2016] [Accepted: 11/30/2016] [Indexed: 11/10/2022]
Abstract
Understanding the relative importance of different ecological processes on the metapopulation dynamics of species is the basis for accurately forecasting metapopulation size in fragmented landscapes. Successful local colonization depends on both species dispersal range and how local habitat conditions affect establishment success. Moreover, there is limited understanding of the effects of different spatiotemporal landscape properties on future metapopulation size. We investigate which factors drive the future metapopulation size of the epiphytic model lichen species Lobaria pulmonaria in a managed forest landscape. First, we test the importance of dispersal and local conditions on the colonization-extinction dynamics of the species using Bayesian state-space modelling of a large-scale data set collected over a 10-yr period. Second, we test the importance of dispersal and establishment limitation in explaining establishment probability and subsequent local population growth, based on a 10-yr propagule sowing experiment. Third, we test how future metapopulation size is affected by different metapopulation and spatiotemporal landscape dynamics, using simulations with the metapopulation models fitted to the empirical data. The colonization probability increased with tree inclination and connectivity, with a mean dispersal distance of 97 m (95% credible intervals, 5-530 m). Local extinctions were mainly deterministic set by tree mortality, but also by tree cutting by forestry. No experimental establishments took place on clearcuts, and in closed forest the establishment probability was higher on trees growing on moist than on dry-mesic soils. The subsequent local population growth rate increased with increasing bark roughness. The simulations showed that the restricted dispersal range estimated (compared to non-restricted dispersal range), and short tree rotation length (65 yr instead of 120) had approximately the same negative effects on future metapopulation size, while regeneration of trees creating a random tree pattern instead of an aggregated one had only some negative effect. However, using the colonization rate obtained with the experimentally added diaspores led to a considerable increase in metapopulation size, making the dispersal limitation of the species clear. The future metapopulation size is thus set by the number of host trees located in shady conditions, not isolated from occupied trees, and by the rotation length of these host trees.
Collapse
Affiliation(s)
- Rocío Belinchón
- Swedish Species Information Centre, Swedish University of Agricultural Sciences, P.O. Box 7007, Uppsala, 75007, Sweden
| | - Philip J Harrison
- Swedish Species Information Centre, Swedish University of Agricultural Sciences, P.O. Box 7007, Uppsala, 75007, Sweden
| | - Louise Mair
- Swedish Species Information Centre, Swedish University of Agricultural Sciences, P.O. Box 7007, Uppsala, 75007, Sweden
| | - Gergely Várkonyi
- Finish Environment Institute, Friendship Park Research Centre, Lentiirantie 342B, Kuhmo, 88900, Finland
| | - Tord Snäll
- Swedish Species Information Centre, Swedish University of Agricultural Sciences, P.O. Box 7007, Uppsala, 75007, Sweden
| |
Collapse
|
9
|
Smith JN, Emlen DJ, Pearson DE. Linking Native and Invader Traits Explains Native Spider Population Responses to Plant Invasion. PLoS One 2016; 11:e0153661. [PMID: 27082240 DOI: 10.1371/journal.pone.0153661] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Accepted: 04/01/2016] [Indexed: 11/19/2022] Open
Abstract
Theoretically, the functional traits of native species should determine how natives respond to invader-driven changes. To explore this idea, we simulated a large-scale plant invasion using dead spotted knapweed (Centaurea stoebe) stems to determine if native spiders' web-building behaviors could explain differences in spider population responses to structural changes arising from C. stoebe invasion. After two years, irregular web-spiders were >30 times more abundant and orb weavers were >23 times more abundant on simulated invasion plots compared to controls. Additionally, irregular web-spiders on simulated invasion plots built webs that were 4.4 times larger and 5.0 times more likely to capture prey, leading to >2-fold increases in recruitment. Orb-weavers showed no differences in web size or prey captures between treatments. Web-spider responses to simulated invasion mimicked patterns following natural invasions, confirming that C. stoebe's architecture is likely the primary attribute driving native spider responses to these invasions. Differences in spider responses were attributable to differences in web construction behaviors relative to historic web substrate constraints. Orb-weavers in this system constructed webs between multiple plants, so they were limited by the overall quantity of native substrates but not by the architecture of individual native plant species. Irregular web-spiders built their webs within individual plants and were greatly constrained by the diminutive architecture of native plant substrates, so they were limited both by quantity and quality of native substrates. Evaluating native species traits in the context of invader-driven change can explain invasion outcomes and help to identify factors limiting native populations.
Collapse
|
10
|
Stephens EL, Quintana-Ascencio PF. Effects of habitat degradation, microsite, and seed density on the persistence of two native herbs in a subtropical shrubland. Am J Bot 2015; 102:1978-1995. [PMID: 26620096 DOI: 10.3732/ajb.1500125] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Accepted: 10/13/2015] [Indexed: 06/05/2023]
Abstract
PREMISE OF THE STUDY Species in degraded ecosystems may interact differently with their surroundings from those under historic conditions. Understanding factors affecting variation in early life history stages of plants is fundamental to assessing their persistence in intact and degraded habitats, and the value of degraded lands. We evaluated the effect of seed density on the seed dynamics of two herbaceous species (annual, biennial), and considered how seed availability may influence population dynamics in different habitats (degraded, intact Florida scrub) and microsites (bare sand, leaf litter, shrub). METHODS We used data on responses to experimental treatments (seed removal, seedling emergence, establishment) and models to evaluate how effects of these factors may change over time since the last disturbance. KEY RESULTS Probability of any seed removal, emergence, and establishment per unit increased with seed density, although proportion removal for Chamaecrista fasciculata, proportion emergence for Balduina angustifolia, and proportion establishment for both species decreased with density. When animals were given selective access to seeds, invertebrates were primarily responsible for seed removal of both study species. Models with dynamics changing with time-since-disturbance for both species predicted that population growth may decrease slightly if local available seed density increases. CONCLUSIONS Detailed demographic comparisons of populations in intact and degraded conditions can be used to understand the way that environmental conditions (habitat, microsite) combine with seed density effects to influence population dynamics of herb species. Degraded habitat may act as a transitional state in a trajectory toward intact conditions for some species, or as refugia for other native species.
Collapse
Affiliation(s)
- Elizabeth L Stephens
- Department of Biology, University of Central Florida, Orlando, Florida 32816-2368 USA
| | | |
Collapse
|
11
|
|
12
|
Grman E, Bassett T, Zirbel CR, Brudvig LA. Dispersal and establishment filters influence the assembly of restored prairie plant communities. Restor Ecol 2015. [DOI: 10.1111/rec.12271] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Emily Grman
- Department of Plant Biology; Michigan State University; 612 Wilson Road East Lansing MI 48824 U.S.A
- Department of Biology; Eastern Michigan University; 441 Mark Jefferson Ypsilanti MI 48197 U.S.A
| | - Tyler Bassett
- Department of Plant Biology; Michigan State University; 612 Wilson Road East Lansing MI 48824 U.S.A
- Kellogg Biological Station; 3700 E Gull Lake Drive Hickory Corners MI 49060 U.S.A
| | - Chad R. Zirbel
- Department of Plant Biology; Michigan State University; 612 Wilson Road East Lansing MI 48824 U.S.A
| | - Lars A. Brudvig
- Department of Plant Biology; Michigan State University; 612 Wilson Road East Lansing MI 48824 U.S.A
| |
Collapse
|
13
|
Gilbert MA, Gaffney EA, Bullock JM, White SM. Spreading speeds for plant populations in landscapes with low environmental variation. J Theor Biol 2014; 363:436-52. [DOI: 10.1016/j.jtbi.2014.08.022] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2014] [Revised: 08/11/2014] [Accepted: 08/13/2014] [Indexed: 11/22/2022]
|
14
|
Houseman GR, Foster BL, Brassil CE. Propagule pressure-invasibility relationships: testing the influence of soil fertility and disturbance with Lespedeza cuneata. Oecologia 2014; 174:511-20. [PMID: 24078081 DOI: 10.1007/s00442-013-2781-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Accepted: 09/10/2013] [Indexed: 10/26/2022]
Abstract
Although invasion risk is expected to increase with propagule pressure (PP), it is unclear whether PP-invasibility relationships follow an asymptotic or some other non-linear form and whether such relationships vary with underlying environmental conditions. Using manipulations of PP, soil fertility and disturbance, we tested how each influence PP-invasibility relationships for Lespedeza cuneata in a Kansas grassland and use recruitment curve models to determine how safe sites may contribute to plant invasions. After three growing seasons, we found that the PP-invasibility relationships best fit an asymptotic model of invasion reflecting a combination of density-independent and density-dependent processes and that seeds were aggregated within the plant community despite efforts to uniformly sow seeds. Consistent with some models, community invasibility decreased with enhanced soil fertility or reduced levels of disturbance in response to changes in the fraction of safe sites. Our results illustrate that disturbance and soil fertility can be a useful organizing principle for predicting community invasibility, asymptotic models are a reasonable starting point for modeling invasion, and new modeling techniques—coupled with classic experimental approaches—can enhance our understanding of the invasion process.
Collapse
|
15
|
Hovick SM, Whitney KD. Hybridisation is associated with increased fecundity and size in invasive taxa: meta-analytic support for the hybridisation-invasion hypothesis. Ecol Lett 2014; 17:1464-77. [PMID: 25234578 PMCID: PMC4231983 DOI: 10.1111/ele.12355] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 06/11/2014] [Accepted: 08/14/2014] [Indexed: 02/04/2023]
Abstract
The hypothesis that interspecific hybridisation promotes invasiveness has received much recent
attention, but tests of the hypothesis can suffer from important limitations. Here, we provide the
first systematic review of studies experimentally testing the hybridisation-invasion (H-I)
hypothesis in plants, animals and fungi. We identified 72 hybrid systems for which hybridisation has
been putatively associated with invasiveness, weediness or range expansion. Within this group, 15
systems (comprising 34 studies) experimentally tested performance of hybrids vs. their parental
species and met our other criteria. Both phylogenetic and non-phylogenetic meta-analyses
demonstrated that wild hybrids were significantly more fecund and larger than their parental taxa,
but did not differ in survival. Resynthesised hybrids (which typically represent earlier generations
than do wild hybrids) did not consistently differ from parental species in fecundity, survival or
size. Using meta-regression, we found that fecundity increased (but survival decreased) with
generation in resynthesised hybrids, suggesting that natural selection can play an important role in
shaping hybrid performance – and thus invasiveness – over time. We conclude that the
available evidence supports the H-I hypothesis, with the caveat that our results are clearly driven
by tests in plants, which are more numerous than tests in animals and fungi.
Collapse
Affiliation(s)
- Stephen M Hovick
- Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, OH, 43210, USA
| | | |
Collapse
|
16
|
Gilbert MA, White SM, Bullock JM, Gaffney EA. Spreading speeds for stage structured plant populations in fragmented landscapes. J Theor Biol 2014; 349:135-49. [DOI: 10.1016/j.jtbi.2014.01.024] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 01/09/2014] [Accepted: 01/21/2014] [Indexed: 11/28/2022]
|
17
|
Miller AL, Diez JM, Sullivan JJ, Wangen SR, Wiser SK, Meffin R, Duncan RP. Quantifying invasion resistance: the use of recruitment functions to control for propagule pressure. Ecology 2014; 95:920-9. [DOI: 10.1890/13-0655.1] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
|
18
|
Quets JJ, Temmerman S, El-Bana MI, Al-Rowaily SL, Assaeed AM, Nijs I. Use of spatial analysis to test hypotheses on plant recruitment in a hyper-arid ecosystem. PLoS One 2014; 9:e91184. [PMID: 24614307 PMCID: PMC3948780 DOI: 10.1371/journal.pone.0091184] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Accepted: 02/10/2014] [Indexed: 11/23/2022] Open
Abstract
Mounds originating from wind-blown sediment accumulation beneath vegetation (nebkhas) often indicate land degradation in dry areas. Thus far, most nebkha research has focused on individual plants. Here, we aimed to explore population-scale processes (up to scales of about 100 m) that might explain an observed nebkha landscape pattern. We mapped the Rhazya stricta Decne. population in a 3 ha study site in a hyper-arid region of Saudi Arabia. We compared the spatial patterns of five different cohorts (age classes) of observed nebkha host plants to those expected under several hypothesized drivers of recruitment and intraspecific interaction. We found that all R. stricta cohorts had a limited fractional vegetation cover and established in large-scale clusters. This clustering weakened with cohort age, possibly indicating merging of neighboring vegetation patches. Different cohort clusters did not spatially overlap in most cases, indicating that recruitment patterns changed position over time. Strong indications were found that the main drivers underlying R. stricta spatial configurations were allogenic (i.e. not driven by vegetation) and dynamic. Most likely these drivers were aeolian-driven sand movement or human disturbance which forced offspring recruitment in spatially dynamic clusters. Competition and facilitation were likely active on the field site too, but apparently had a limited effect on the overall landscape structure.
Collapse
Affiliation(s)
- Jan J. Quets
- Plant and Vegetation Ecology (PLECO), Department of Biology, University of Antwerp, Wilrijk, Belgium
- * E-mail:
| | - Stijn Temmerman
- Ecosystem Management, Department of Biology, University of Antwerp, Wilrijk, Belgium
| | - Magdy I. El-Bana
- Department of Botany, Faculty of Science, Port Said University, Port Said, Egypt
| | - Saud L. Al-Rowaily
- Department of Plant Production, College of Agriculture, King Saud University, Riyadh, Saudi Arabia
| | - Abdulaziz M. Assaeed
- Department of Plant Production, College of Agriculture, King Saud University, Riyadh, Saudi Arabia
| | - Ivan Nijs
- Plant and Vegetation Ecology (PLECO), Department of Biology, University of Antwerp, Wilrijk, Belgium
| |
Collapse
|
19
|
|
20
|
Clark CJ, Poulsen JR, Levey DJ. Roles of seed and establishment limitation in determining patterns of afrotropical tree recruitment. PLoS One 2013; 8:e63330. [PMID: 23691023 PMCID: PMC3653939 DOI: 10.1371/journal.pone.0063330] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Accepted: 03/31/2013] [Indexed: 11/17/2022] Open
Abstract
Quantifying the relative importance of the multiple processes that limit recruitment may hold the key to understanding tropical tree diversity. Here we couple theoretical models with a large-scale, multi-species seed-sowing experiment to assess the degree to which seed and establishment limitation shape patterns of tropical tree seedling recruitment in a central African forest. Of five randomly selected species (Pancovia laurentii, Staudtia kamerunensis, Manilkara mabokeensis, Myrianthus arboreas, and Entandophragma utile), seedling establishment and survival were low (means of 16% and 6% at 3 and 24 months, respectively), and seedling density increased with seed augmentation. Seedling recruitment was best explained by species identity and the interaction of site-by-species, suggesting recruitment probabilities vary among species and sites, and supporting the role of niche-based mechanisms. Although seed augmentation enhanced initial seedling density, environmental filtering and post-establishment mortality strongly limited seedling recruitment. The relative importance of seed and establishment limitation changed with seed and seedling density and through time. The arrival of seeds most strongly affected local recruitment when seeds were nearly absent from a site (∼ 1 seed m2), but was also important when seeds arrived in extremely high densities, overwhelming niche-based mortality factors. The strength of seed limitation and density-independent mortality decreased significantly over time, while density-dependent mortality showed the opposite trend. The varying strengths of seed and establishment limitation as a function of juvenile density and time emphasize the need to evaluate their roles through later stages of a tree’s life cycle.
Collapse
Affiliation(s)
- Connie J Clark
- Nicholas School of the Environment, Duke University, Durham, North Carolina, USA
| | | | | |
Collapse
|
21
|
Nelis LC. Life form and life history explain variation in population processes in a grassland community invaded by exotic plants and mammals. PLoS One 2012; 7:e42906. [PMID: 22916178 DOI: 10.1371/journal.pone.0042906] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2012] [Accepted: 07/13/2012] [Indexed: 11/19/2022] Open
Abstract
The existence of general characteristics of plant invasiveness is still debated. One reason we may not have found these characteristics is because we do not yet understand how processes underlying population dynamics contribute to community composition in invaded communities. Here I modify Ricker stock-recruitment models to parameterize processes important to community dynamics in an invaded grassland community: immigration, maximum intrinsic growth rate, self-regulation, and limitation by other species. I then used the parameterized models in a multi-species stochastic simulation to determine how processes affected long-term community dynamics. By parameterizing the models using the frequency of the 18 most common species in the grassland, I determined that life history and life form are stronger predictors of underlying processes than is native status. Immigration maintains exotic annual grasses and the dominant native perennial grass in the community. Growth rate maintains other perennial species. While the model mirrors the frequency of native species well, exotic species have lower observed than parameterized frequencies, suggesting that they are not reaching their potential frequency. These results, combined with results from past research, suggest that disturbance may be key to maintaining exotic species in the community. Here I showed that a continuous modified Ricker model fit discrete grassland frequency data well. This allowed me to model the dominant species in the community simultaneously and gain insight into the processes that determine community composition.
Collapse
|
22
|
Abstract
The loss of animals in tropical forests may alter seed dispersal patterns and reduce seedling recruitment of tree species, but direct experimental evidence is scarce. We manipulated dispersal patterns of Manilkara mabokeensis, a monkey-dispersed tree, to assess the extent to which spatial distributions of seeds drive seedling recruitment. Based on the natural seed shadow, we created seed distributions with seeds deposited under the canopy ("no dispersal"), with declining density from the tree ("natural dispersal"), and at uniform densities ("good dispersal"). These distributions mimicked dispersal patterns that could occur with the extirpation of monkeys, low levels of hunting, and high rates of seed dispersal. We monitored seedling emergence and survival for 18 months and recorded the number of leaves and damage to leaves. "Good dispersal" increased seedling survival by 26%, and "no dispersal" decreased survival by 78%, relative to "natural dispersal." Using a mixed-effects survival model, we decoupled the distance and density components of the seed shadow: seedling survival depended on the seed density, but not on the distance from the tree. Although community seedling diversity tended to decrease with longer dispersal distances, we found no conclusive evidence that patterns of seed dispersal influence the diversity of the seedling community. Local seed dispersal does affect seedling recruitment and survival, with better dispersal resulting in higher seedling recruitment; hence the loss of dispersal services that comes with the reduction or extirpation of seed dispersers will decrease regeneration of some tree species.
Collapse
Affiliation(s)
- John R Poulsen
- Nicholas School of the Environment, Duke University, P.O. Box 90328, Durham, North Carolina 27708, USA.
| | | | | |
Collapse
|
23
|
Abstract
In tropical forests, resource-based niches and density-dependent mortality are mutually compatible mechanisms that can act simultaneously to limit seedling populations. Differences in the strengths of these mechanisms will determine their roles in maintaining species coexistence. In the first assessment of these mechanisms in a Congo Basin forest, we quantified their relative strengths and tested the extent to which density-dependent mortality is driven by the distance-dependent behavior of seed and seedling predators predicted by the Janzen-Connell hypothesis. We conducted a large-scale seed addition experiment for five randomly selected tropical tree species, caging a subset of seed addition quadrats against vertebrate predators. We then developed models to assess the mechanisms that determine seedling emergence (three months after seed addition) and survival (two years after seed addition). As predicted, both niche differentiation and density-dependent mortality limited seedling recruitment, but predation had the strongest effects on seedling emergence and survival. Seedling species responded differently to naturally occurring environmental variation among sites, including variation in light levels and soil characteristics, supporting predictions of niche-based theories of tropical tree species coexistence. The addition of higher densities of seeds into quadrats initially led to greater seedling emergence, but survival to two years decreased with seed density. Seed and seedling predation reduced recruitment below levels maintained by density-dependent mortality, an indication that predators largely determine the population size of tree seedlings. Seedling recruitment was unrelated to the distance to or density of conspecific adult trees, suggesting that recruitment patterns are generated by generalist vertebrate herbivores rather than the specialized predators predicted by the Janzen-Connell hypothesis. If the role of seed and seedling predation in limiting seedling recruitment is a general phenomenon, then the relative abundances of tree species might largely depend on species-specific adaptations to avoid, survive, and recover from damage induced by vertebrate herbivores. Likewise, population declines of herbivorous vertebrate species (many of which are large and hunted) may trigger shifts in species composition of tropical forests.
Collapse
Affiliation(s)
- C J Clark
- Nicholas School of the Environment, Duke University, P.O. Box 90328, Durham, North Carolina 27708, USA.
| | | | | |
Collapse
|
24
|
Abstract
The recovery of native communities after cultivation may be constrained by (a) the failure of species to reach a site or (b) their failure to survive once there. Although seed addition is a common method to test for seed versus microsite limitation, most studies do not follow populations beyond seedling establishment, nor do they measure seed dispersal. We examined dispersal across native grassland/old field boundaries and investigated the relative importance of seed and microsite limitation across multiple life-history stages and generations. Seed trapping showed little movement of native seeds into old fields and that most species had extremely localized dispersal. Consequently, there was no pattern of seed density with distance from boundaries, and similarity between the seed rain and standing vegetation was moderate to high. Seed addition showed that two annual species were able to establish in all, and flower in most, subplots in the first year, and that seedling establishment increased with sowing density, consistent with seed limitation. However, the relative importance of microsite limitation increased over the lifespans of the species. Density dependence reduced the number of flowering plants, resulting in a large decline in seedling density in the following generation. This decline continued so that the initial positive effect of sowing density on seedling numbers disappeared by the fourth generation and hence the persistence of populations is uncertain. Thus, by monitoring seed dispersal and following experimental populations beyond seedling establishment, we showed that dispersal limits species distributions, but microsite plays an important role in limiting population growth and persistence.
Collapse
Affiliation(s)
- Andrew J Scott
- Department of Botany, La Trobe University, Bundoora, Melbourne, VIC, 3086, Australia.
| | | |
Collapse
|
25
|
Warren RJ, Bahn V, Bradford MA. The interaction between propagule pressure, habitat suitability and density-dependent reproduction in species invasion. OIKOS 2011. [DOI: 10.1111/j.1600-0706.2011.20174.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
26
|
Aicher RJ, Larios L, Suding KN. Seed Supply, Recruitment, and Assembly: Quantifying Relative Seed and Establishment Limitation in a Plant Community Context. Am Nat 2011; 178:464-77. [DOI: 10.1086/661900] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
|
27
|
|
28
|
Abstract
Ecological theory suggests that both dispersal limitation and resource limitation can exert strong effects on community assembly. However, empirical studies of community assembly have focused almost exclusively on communities with a single trophic level. Thus, little is known about the combined effects of dispersal and resource limitation on assembly of communities with multiple trophic levels. We performed a landscape-scale experiment using spatially arranged mesocosms to study effects of dispersal and resource limitation on the assembly dynamics of aquatic invertebrate communities with two trophic levels. We found that interplay between dispersal and resource limitation regulated the assembly of predator and prey trophic levels in these pond communities. Early in assembly, predators and prey were strongly dispersal limited, and resource (i.e., prey) availability did not influence predator colonization. Later in assembly, after predators colonized, resource limitation was the strongest driver of predator abundance, and dispersal limitation played a negligible role. Thus, habitat isolation affected predators directly by reducing predator colonization rate, and indirectly through the effect of distance on prey availability. Dispersal and resource limitation of predators resulted in a transient period in which predators were absent or rare in isolated habitats. This period may be important for understanding population dynamics of vulnerable prey species. Our findings demonstrate that dispersal and resource limitation can jointly regulate assembly dynamics in multi-trophic systems. They also highlight the need to develop a temporal picture of the assembly process in multi-trophic communities because the availability and spatial distribution of limiting resources (i.e., prey) and the distribution of predators can shift radically over time.
Collapse
Affiliation(s)
- Andrew M Hein
- Department of Biology, University of Florida, Gainesville, Florida 32611-8525, USA.
| | | |
Collapse
|
29
|
Hierro JL, Lortie CJ, Villarreal D, Estanga-Mollica ME, Callaway RM. Resistance to Centaurea solstitialis invasion from annual and perennial grasses in California and Argentina. Biol Invasions 2011. [DOI: 10.1007/s10530-011-0037-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
30
|
Abstract
Although global declines in frugivores may disrupt seed dispersal mutualisms and inhibit plant recruitment, quantifying the likely reduction in plant regeneration has been difficult and rarely attempted. We use a manipulative factorial experiment to quantify dependence of recruitment on dispersal (i.e. fruit pulp removal and movement of seed away from parental area) in two large-seeded New Zealand tree species. Complete dispersal failure would cause a 66 to 81 per cent reduction in recruitment to the 2-year-old seedling stage, and synergistic interactions with introduced mammalian seed and seedling predators increase the reduction to 92 to 94 per cent. Dispersal failure reduced regeneration through effects on seed predation, germination and (especially) seedling survival, including distance- and density-dependent (Janzen-Connell) effects. Dispersal of both species is currently largely dependent on a single frugivore, and many fruits today remain uneaten. Present-day levels of frugivore loss and mammal seed and seedling predators result in 57 to 84 per cent fewer seedlings after 2 years. Our study demonstrates the importance of seed dispersal for local plant population persistence, and validates concerns about the community consequences of frugivore declines.
Collapse
Affiliation(s)
- Debra M Wotton
- School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand.
| | | |
Collapse
|
31
|
|
32
|
Affiliation(s)
- Scott C Burgess
- School of Biological Sciences, University of Queensland, Brisbane, Qld 4072, Australia.
| | | |
Collapse
|
33
|
García-Camacho R, Iriondo JM, Escudero A. Seedling dynamics at elevation limits: Complex interactions beyond seed and microsite limitations. Am J Bot 2010; 97:1791-1797. [PMID: 21616818 DOI: 10.3732/ajb.1000248] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
PREMISE OF THE STUDY Limited availability of seeds and microsites are important constraints for seedling emergence and survival. However, little is known about population-level feedbacks between seed and microsite limitation and how these relationships vary in contrasting conditions. Focusing on Armeria caespitosa, a high-mountain endemic, we asked whether seedling establishment was simultaneously limited by seed and microsite availability, whether the balance between seed and microsite limitations varied with contrasting environments, and whether seed and microsite limitations interacted with each other. • METHODS We studied seedling emergence and survival at the edges of the elevation range of A. caespitosa in central Spain over 4 years. We used mixed linear models and structural equation modeling. • KEY RESULTS Our results showed that A. caespitosa recruits similar numbers of new seedlings per plot in contrasting environments. Seedling emergence and survival in A. caespitosa were both limited by seed and microsite availability. Habitat suitability (the surrogate of microsite limitation) varied between populations and indirectly affected fertility (the surrogate of seed limitation). • CONCLUSIONS Seedling emergence and survival are both seed and microsite limited, there are interactions between seed and microsite limitations, and both factors, which control seedling establishment, and their interconnections, vary among local populations.
Collapse
Affiliation(s)
- Raúl García-Camacho
- Department of Plant Ecology, University of Tübingen, Auf der Morgenstelle 3 72076 Tübingen, Germany
| | | | | |
Collapse
|
34
|
|
35
|
Abstract
Seed and establishment limitation can have a major role in determining plant species' abundances and distributions in communities. Their relative importance, however, remains uncertain and controversial, especially for trees in forests where density-dependent mortality of seeds and seedlings may be common. In a primary African rain forest, we directly tested the strength of each limitation by using seeds of the tree species Microberlinia bisulcata and Tetraberlinia bifoliolata at eight addition levels and by following establishment over six weeks. Local background seed rain was also measured. Seedling recruitment was higher in seed-addition quadrats than in control quadrats, indicating seed limitation in both species. However, fitting the Beverton-Holt model indicated that establishment limitation was consistently 2-4 times stronger than seed limitation for Microberlinia, whereas seed limitation greatly exceeded establishment limitation for Tetraberlinia. Strong density dependence was operating in the short seed-to-seedling transition for Microberlinia, whereas it was almost negligible for Tetraberlinia. Although early postdispersal mortality was very high for both species (> 80%), they may achieve local codominance as a result of differing strengths of seed limitation vs. establishment limitation. Assessing the importance of seed limitation for tree populations requires a knowledge of species-specific seed rain as well as a reliable recruitment function. The outcome of early establishment processes also needs to be seen in the context of later stages of tree dynamics.
Collapse
Affiliation(s)
- Julian M Norghauer
- Institute of Plant Sciences, University of Bern, Altenbergrain 21, Bern 3013, Switzerland.
| | | |
Collapse
|
36
|
Kolb A, Barsch K. Environmental factors and seed abundance influence seedling emergence of a perennial forest herb. Acta Oecologica 2010. [DOI: 10.1016/j.actao.2010.07.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
37
|
Abstract
Debates concerning the roles of different factors that may limit an organism's reproductive success pervade evolutionary ecology. We suggest that a broad class of limiting-factors problems involving essential resources or essential components of reproductive effort can be analyzed with an evolutionary application of Liebig's law of the minimum. We explore life-history evolution using the metaphor of an organism that must harvest two essential resources (resources 1 and 2) from a stochastically varying environment. Our models make three predictions. First, organisms should overinvest, relative to the deterministic case, in harvesting the resource whose per-offspring harvest cost is smaller. Second, at the optimum, organisms balance multiple fitness-limiting factors rather than being consistently limited by one factor. Third, the optimal investment in harvesting a resource is directly linked to the probability that the organism's fitness will be limited by that resource. Under temporal variation, the optimal proportional investment in harvesting resource 1 is equal to the probability that resource 1 will limit fitness. Our results help to explain why the responses of populations to environmental perturbations are hard to predict: as an organism transitions between different limiting factors, its responses to perturbations of those factors will likewise change.
Collapse
Affiliation(s)
- Jay A Rosenheim
- Department of Entomology and Center for Population Biology, University of California, Davis, California 95616, USA.
| | | | | |
Collapse
|
38
|
Swope SM, Parker IM. Widespread seed limitation affects plant density but not population trajectory in the invasive plant Centaurea solstitialis. Oecologia 2010; 164:117-28. [PMID: 20443027 DOI: 10.1007/s00442-010-1641-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Accepted: 04/12/2010] [Indexed: 10/19/2022]
Abstract
In some plant populations, the availability of seeds strongly regulates recruitment. However, a scarcity of germination microsites, granivory or density-dependent mortality can reduce the number of plants that germinate or survive to flower. The relative strengths of these controls are unknown for most plant populations and for exotic invaders in particular. We conducted a seed addition experiment with a granivore exclusion treatment in a field setting to explore how these factors interact to regulate populations of the widespread invader Centaurea solstitialis (yellow starthistle) at three study sites across the plant's range in California. We coupled the experimental approach with observational studies within established C. solstitialis populations to estimate seed rain, recruitment and mortality at natural densities. Seed limitation occurred in both experimental and observational plots in all populations. Although vertebrate granivores were active at each site, they had no effect on C. solstitialis recruitment. Density increased mortality, but the effect was variable and weak relative to its effect on fecundity. The seed limitation that was evident at the seedling stage persisted to flowering. Seed-limited populations such as these ought to be highly sensitive to losses to seed predators, and many biological control agents, including those established for C. solstitialis, are seed predators. However, flowering plant density was decoupled from seed production by a strong compensatory response in the surviving plants; seed production was nearly constant in plots across all seed addition levels. Thus, flowering plant density is reduced by the established biocontrol agents, but seed production compensates to replace the population every generation, and no long-term decline is predicted.
Collapse
|
39
|
Abstract
Seed production and seedling recruitment are thought to be of minor importance in determining population dynamics and long-term viability in long-lived perennial plants. Seed addition experiments, on the other hand, have amply shown that supplemental addition of seeds almost always, irrespective of longevity, results in increased seedling recruitment. Any change in the environment that affects fruit and seed production can thus be expected to affect seedling recruitment, but the extent to which increased fruit and seed production affect overall population dynamics remains relatively unknown. In this paper, we present demographic data of six populations of the long-lived woodland orchid Orchis purpurea that were monitored for seven consecutive years (2002-2008) occurring in two contrasting light environments. We use a nested life table response experiment (LTRE) at the vital rate level to disentangle the relative contributions of each of six annual transitions, six sites, and two light environments on the population dynamics of this species and to determine vital rate variations that contributed most to variation in population growth rate. Population growth rates (lamda) were significantly higher in the light environment than in the shaded environment (average lamda = 0.9930 and 1.0492 in the shaded and light environment, respectively). The LTRE analysis showed that variation in fecundity and, to a lesser extent, variation in growth made the largest total contributions to variation in lamda, whereas the contributions of variation in survival were almost negligible. Fruit production was two times larger and the net reproductive rate (R0) was approximately six times higher in the light environment than in shaded areas, suggesting that variables related to reproduction are the key drivers of population dynamics of this long-lived orchid species in different light environments. Our results indicate that light is an important factor affecting population dynamics of Orchis purpurea and illustrate that, even in long-lived species, flower and seed production can have important effects on the population dynamics.
Collapse
Affiliation(s)
- Hans Jacquemyn
- Division of Plant Ecology and Systematics, University of Leuven, Arenbergpark 31, B-3001 Heverlee, Belgium.
| | | | | |
Collapse
|
40
|
Abstract
Although post-dispersal seed predators are common and often reduce seed density, their influence on plant population abundance remains unclear. On the one hand, increasing evidence suggests that many plant populations are seed limited, implying that seed predators could reduce plant abundance. On the other hand,.it is generally uncertain whether the magnitude of seed limitation imposed by granivores is strong enough to overcome density-dependent processes that could compensate for seed loss at later stages. We examined the impact of seed predation by small mammals, primarily deer mice (Peromyscus maniculatus), on seedling recruitment and subsequent plant establishment of two perennial grassland forbs in western Montana, USA: Lupinus sericeus (Fabaceae) and Lithospermum ruderale (Boraginaceae). The experiment combined graded densities of seed addition for each species with a small-mammal exclusion treatment. Seedling recruitment and plant establishment were monitored in the experimental plots for up to three years. For both species, small-mammal exclusion increased the total number of seedlings that emerged, and these effects were still significant three years after seed addition, resulting in greater numbers of established plants inside exclosures than in control plots. We also found evidence of seed limitation, with increasing density of seeds added leading to increased numbers of seedlings. Results from seed addition and small-mammal exclusion experiments in later years also revealed significant impacts of small mammals on seedling emergence. These results suggest that granivores can have potentially important impacts in limiting forb abundance in grasslands communities.
Collapse
Affiliation(s)
- Mary Bricker
- Division of Biological Sciences, University of Montana, Missoula, Montana 59812, USA.
| | | | | |
Collapse
|
41
|
Jacquemyn H, Endels P, Honnay O, Wiegand T. Evaluating management interventions in small populations of a perennial herbPrimula vulgarisusing spatio-temporal analyses of point patterns. J Appl Ecol 2010. [DOI: 10.1111/j.1365-2664.2010.01778.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
42
|
Lancaster J, Downes BJ, Arnold A. Environmental constraints on oviposition limit egg supply of a stream insect at multiple scales. Oecologia 2010; 163:373-84. [DOI: 10.1007/s00442-010-1565-9] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2009] [Accepted: 01/07/2010] [Indexed: 11/24/2022]
|
43
|
Downes BJ, Lancaster J. Does dispersal control population densities in advection-dominated systems? A fresh look at critical assumptions and a direct test. J Anim Ecol 2010; 79:235-48. [DOI: 10.1111/j.1365-2656.2009.01620.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
44
|
Abstract
1. Savanna ecosystems are defined largely by tree-grass mixtures, and tree establishment is a key driver of community structure and ecosystem function in these systems. The factors controlling savanna tree establishment are understudied, but likely involve some combination of seed, microsite and predator/fire limitation. In African savannas, suppression and killing of adult trees by large mammals like elephants (Loxodonta africana Blumenbach, 1797) and giraffes (Giraffa camelopardalis Linnaeus, 1758) can maintain tree-grass co-dominance, although the impacts of even these conspicuous herbivores on tree establishment also are poorly understood. 2. We combined seed addition and predator exclusion experiments with a large-scale, long-term field manipulation of large herbivores to investigate the relative importance of seeds, microsites and predators in limiting establishment of a monodominant tree (Acacia drepanolobium Sjostedt) in a Kenyan savanna. 3. Both wild and domestic (i.e. cattle; Bos taurus Linnaeus, 1758) large herbivores facilitated tree establishment by suppressing abundances of rodents, the most important seed and seedling predators. However, this indirect, positive effect of wild herbivores was negated by wild herbivores' suppression of seed production. Cattle did not have this direct, negative impact; rather, they further assisted tree establishment by reducing cover of understorey grasses. Thus, the impacts of both groups of large herbivores on tree establishment were largely routed through other taxa, with a negligible net effect of wild herbivores and a positive net effect of cattle on tree establishment. 4. The distinction between the (positive) net effect of cattle and (neutral) net effect of wild herbivores is due to the inclusion of browsers and mixed feeders within the assemblage of wild herbivores. Browsing by wild herbivores limited seed production, which reduced tree recruitment; grazing by cattle was more pronounced than that by wild herbivores, and thus promoted germination and subsequent establishment of small trees. 5. Our study is the first to link seed fates to tree establishment in savanna ecosystems in experimentally-manipulated herbivore communities. Further, our results highlight how large herbivores can modify a suite of independent factors - seed production, competition with understorey species, and seed and seedling predation - to collectively drive tree establishment.
Collapse
Affiliation(s)
- Jacob R Goheen
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
| | | | | | | | | |
Collapse
|
45
|
Iacona GD, Kirkman LK, Bruna EM. Effects of resource availability on seedling recruitment in a fire-maintained savanna. Oecologia 2009; 163:171-80. [PMID: 19921271 DOI: 10.1007/s00442-009-1502-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Accepted: 10/27/2009] [Indexed: 11/25/2022]
Affiliation(s)
- Gwenllian D Iacona
- Department of Wildlife Ecology and Conservation, University of Florida, PO Box 110430, Gainesville, FL 32611-0430, USA.
| | | | | |
Collapse
|
46
|
Affiliation(s)
- Richard P Duncan
- Bio-Protection Research Centre, P.O. Box 84, Lincoln University, Lincoln 7647, New Zealand.
| | | | | | | | | |
Collapse
|
47
|
Pearson DE. Invasive plant architecture alters trophic interactions by changing predator abundance and behavior. Oecologia 2008; 159:549-58. [DOI: 10.1007/s00442-008-1241-5] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2008] [Accepted: 11/14/2008] [Indexed: 11/29/2022]
|
48
|
Abstract
Small-mammal seed predation is an important force structuring native-plant communities that may also influence exotic-plant invasions. In the intermountain West, deer mice (Peromyscus maniculatus) are prominent predators of native-plant seeds, but they avoid consuming seeds of certain widespread invasives like spotted knapweed (Centaurea maculosa). These mice also consume the biological-control insects Urophora spp. introduced to control C. maculosa, and this food resource substantially increases deer mouse populations. Thus, mice may play an important role in the invasion and management of C. maculosa through food-web interactions. We examined deer mouse seed predation and its effects on seedling emergence and establishment of a dominant native grass, Pseudoroegneria spicata, and forb, Balsamorhiza sagittata, in C. maculosa-invaded grasslands that were treated with herbicide to suppress C. maculosa or left untreated as controls. Deer mice readily took seeds of both native plants but removed 2-20 times more of the larger B. sagittata seeds than the smaller P. spicata seeds. Seed predation reduced emergence and establishment of both species but had greater impacts on B. sagittata. The intensity of seed predation corresponded with annual and seasonal changes in deer mouse abundance, suggesting that abundance largely determined mouse impacts on native-plant seeds. Accordingly, herbicide treatments that reduced mouse abundance by suppressing C. maculosa and its associated biocontrol food subsidies to mice also reduced seed predation and decreased the impact of deer mice on B. sagittata establishment. These results provide evidence that Urophora biocontrol agents may exacerbate the negative effects of C. maculosa on native plants through a form of second-order apparent competition-a biocontrol indirect effect that has not been previously documented. Herbicide suppressed C. maculosa and Urophora, reducing mouse populations and moderating seed predation on native plants, but the herbicide's direct negative effects on native forb seedlings overwhelmed the indirect positive effect of reducing deer mouse seed predation. By manipulating this four-level food chain, we illustrate that host-specific biological control agents may impact nontarget plant species through food-web interactions, and herbicides may influence management outcomes through indirect trophic interactions in addition to their direct effects on plants.
Collapse
Affiliation(s)
- Dean E Pearson
- Rocky Mountain Research Station, USDA Forest Service, 800 E. Beckwith Avenue, Missoula, Montana 59801, USA.
| | | |
Collapse
|