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Johnson CR, Dudgeon S. Understanding change in benthic marine systems. ANNALS OF BOTANY 2024; 133:131-144. [PMID: 38079203 PMCID: PMC10921837 DOI: 10.1093/aob/mcad187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Accepted: 12/10/2023] [Indexed: 03/09/2024]
Abstract
BACKGROUND The unprecedented influence of human activities on natural ecosystems in the 21st century has resulted in increasingly frequent large-scale changes in ecological communities. This has heightened interest in understanding such changes and effective means to manage them. Accurate interpretation of state changes is challenging because of difficulties translating theory to empirical study, and most theory emphasizes systems near equilibrium, which may not be relevant in rapidly changing environments. SCOPE We review concepts of long-transient stages and phase shifts between stable community states, both smooth, continuous and discontinuous shifts, and the relationships among them. Three principal challenges emerge when applying these concepts. The first is how to interpret observed change in communities - distinguishing multiple stable states from long transients, or reversible shifts in the phase portrait of single attractor systems. The second is how to quantify the magnitudes of three sources of variability that cause switches between community states: (1) 'noise' in species' abundances, (2) 'wiggle' in system parameters and (3) trends in parameters that affect the topography of the basin of attraction. The third challenge is how variability of the system shapes evidence used to interpret community changes. We outline a novel approach using critical length scales to potentially address these challenges. These concepts are highlighted by a review of recent examples involving macroalgae as key players in marine benthic ecosystems. CONCLUSIONS Real-world examples show three or more stable configurations of ecological communities may exist for a given set of parameters, and transient stages may persist for long periods necessitating their respective consideration. The characteristic length scale (CLS) is a useful metric that uniquely identifies a community 'basin of attraction', enabling phase shifts to be distinguished from long transients. Variabilities of CLSs and time series data may likewise provide proactive management measures to mitigate phase shifts and loss of ecosystem services. Continued challenges remain in distinguishing continuous from discontinuous phase shifts because their respective dynamics lack unique signatures.
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Affiliation(s)
- Craig R Johnson
- Institute for Marine & Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania, Australia 7001, and
| | - Steve Dudgeon
- Department of Biology, California State University, Northridge, CA 91330-8303, USA
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Ebert D, Reinert A, Fisher B. Visual Analytics Review: An Early and Continuing Success of Convergent Research With Impact. Comput Sci Eng 2021. [DOI: 10.1109/mcse.2021.3069342] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Wilcox C, Carlile N, Hardesty BD, Reid T. Assessing multiple threats to seabird populations using flesh-footed shearwaters Ardenna carneipes on Lord Howe Island, Australia as case study. Sci Rep 2021; 11:7196. [PMID: 33785816 PMCID: PMC8009916 DOI: 10.1038/s41598-021-86702-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Accepted: 02/23/2021] [Indexed: 11/26/2022] Open
Abstract
Globally, seabird populations have been in decline due to multiple threats throughout their range. Separating simultaneous pressures is challenging and can require significant amounts of data over long periods of time. We use spatial contrasts to investigate the relative importance of several drivers for the purported decline in a species listed as in decline as an example species, the Flesh-footed shearwater (Ardenna carneipes). On Lord Howe Island in the Tasman Sea, Australia, this seabird suffers from habitat loss due to housing development, intensive mortality in fisheries, plastic ingestion, and roadkill due to vehicular traffic on its breeding island. We repeated a quantitative survey of the population to ascertain whether the decline previously reported had continued and to evaluate the purported mortality sources (Reid et al. in PLoS ONE 8(4):e58230, 2013, Lavers et al. in Global Ecol Conserv 17:e00579, 2019). We measured burrow density, area of occurrence, occupancy and breeding success, integrating them with previous surveys using a Bayesian statistical model to generate longer term estimates of demographic rates. We used spatial patterns to test whether mortality on roads or proximity to human habitation was influencing population demographics. In contrast to predictions, we found the population had stabilised or increased. Characteristics such as burrow occupancy and breeding success showed little pattern, with weak evidence for impacts from road mortality and housing development. Such a data-rich approach is substantially more informative and can better support seabird conservation and management efforts does require more field-time and additional equipment than most contemporary surveys, the data is substantially more informative and can better clarify the results of efforts in seabird conservation and management.
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Affiliation(s)
- Chris Wilcox
- CSIRO Oceans and Atmosphere, Hobart, TAS, 7000, Australia
| | - Nicholas Carlile
- Department of Planning, Industry and Environment, Parramatta, NSW, 2150, Australia
| | | | - Tim Reid
- Institute for Applied Ecology, University of Canberra, Bruce, ACT, 2617, Australia. .,CSIRO Oceans and Atmosphere, Hobart, TAS, 7000, Australia.
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Kulha N, Pasanen L, Holmström L, De Grandpré L, Kuuluvainen T, Aakala T. At What Scales and Why Does Forest Structure Vary in Naturally Dynamic Boreal Forests? An Analysis of Forest Landscapes on Two Continents. Ecosystems 2018. [DOI: 10.1007/s10021-018-0297-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Ward DFL, Wotherspoon S, Melbourne-Thomas J, Haapkylä J, Johnson CR. Detecting ecological regime shifts from transect data. ECOL MONOGR 2018. [DOI: 10.1002/ecm.1312] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Delphi F. L. Ward
- Institute for Marine and Antarctic Studies; University of Tasmania; Private Bag 129 Hobart Tasmania 7001 Australia
- Antarctic Climate & Ecosystems Cooperative Research Centre; University of Tasmania; Private Bag 80 Hobart Tasmania 7001 Australia
| | - Simon Wotherspoon
- Institute for Marine and Antarctic Studies; University of Tasmania; Private Bag 129 Hobart Tasmania 7001 Australia
- Australian Antarctic Division; Department of the Environment and Energy; 203 Channel Highway Kingston Tasmania 7050 Australia
| | - Jessica Melbourne-Thomas
- Antarctic Climate & Ecosystems Cooperative Research Centre; University of Tasmania; Private Bag 80 Hobart Tasmania 7001 Australia
- Australian Antarctic Division; Department of the Environment and Energy; 203 Channel Highway Kingston Tasmania 7050 Australia
| | - Jessica Haapkylä
- School of Marine and Tropical Biology; ARC Centre of Excellence for Coral Reef Studies; James Cook University; Townsville Queensland 4811 Australia
| | - Craig R. Johnson
- Institute for Marine and Antarctic Studies; University of Tasmania; Private Bag 129 Hobart Tasmania 7001 Australia
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Contrasting responses of functional diversity to major losses in taxonomic diversity. Proc Natl Acad Sci U S A 2018; 115:732-737. [PMID: 29305556 DOI: 10.1073/pnas.1717636115] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Taxonomic diversity of benthic marine invertebrate shelf species declines at present by nearly an order of magnitude from the tropics to the poles in each hemisphere along the latitudinal diversity gradient (LDG), most steeply along the western Pacific where shallow-sea diversity is at its tropical maximum. In the Bivalvia, a model system for macroevolution and macroecology, this taxonomic trend is accompanied by a decline in the number of functional groups and an increase in the evenness of taxa distributed among those groups, with maximum functional evenness (FE) in polar waters of both hemispheres. In contrast, analyses of this model system across the two era-defining events of the Phanerozoic, the Permian-Triassic and Cretaceous-Paleogene mass extinctions, show only minor declines in functional richness despite high extinction intensities, resulting in a rise in FE owing to the persistence of functional groups. We hypothesize that the spatial decline of taxonomic diversity and increase in FE along the present-day LDG primarily reflect diversity-dependent factors, whereas retention of almost all functional groups through the two mass extinctions suggests the operation of diversity-independent factors. Comparative analyses of different aspects of biodiversity thus reveal strongly contrasting biological consequences of similarly severe declines in taxonomic diversity and can help predict the consequences for functional diversity among different drivers of past, present, and future biodiversity loss.
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Johnson CR, Chabot RH, Marzloff MP, Wotherspoon S. Knowing when (not) to attempt ecological restoration. Restor Ecol 2016. [DOI: 10.1111/rec.12413] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Craig R. Johnson
- Institute for Marine and Antarctic Studies University of Tasmania Private Bag 129 Hobart Tasmania 7001 Australia
| | - Rebecca H. Chabot
- Institute for Marine and Antarctic Studies University of Tasmania Private Bag 129 Hobart Tasmania 7001 Australia
| | - Martin P. Marzloff
- Institute for Marine and Antarctic Studies University of Tasmania Private Bag 129 Hobart Tasmania 7001 Australia
| | - Simon Wotherspoon
- Institute for Marine and Antarctic Studies University of Tasmania Private Bag 129 Hobart Tasmania 7001 Australia
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Larson-Praplan S, George MR, Buckhouse JC, Laca EA. Spatial and temporal domains of scale of grazing cattle. ANIMAL PRODUCTION SCIENCE 2015. [DOI: 10.1071/an14641] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Spatio-temporal patterns of cattle grazing were studied in four annual grassland pastures in California, differing mainly in tree canopy cover. Cows were equipped with global positioning collars that recorded position, temperature and head movements at 5-min intervals during 6 days in each of four seasons repeated during 2 years. The time animals took to traverse areas of varying diameter revealed patches of 6–9-m diameter in the pastures with low, and 18–21-m diameter in the pastures with high tree canopy cover. In agreement with the current model, crookedness of cow paths had two distinct domains. Within distances of 0–40 m, paths were relatively straight and similar, but from 40 to 200 m, they became increasingly tortuous. Correlation of sequential turning angles identified patches of movement with diameters between 40 and 100 m, which correspond to the ‘patch’ level of grazing within grazing sites. Seasonal changes in meal patterns were consistent with changes in temperature and forage quality and interacted with the distribution of shade. Thus, spatial distribution of grazing and temporal distribution of meals were inextricably linked. Low forage quality and high temperatures in summer resulted in highly concentrated grazing around trees. Conversely, winter and early spring forages of very high quality and low availability motivated more widely distributed grazing, with low proportion of areas being re-grazed. Resting sites acted as beginning and end of grazing bouts. We conclude that shade distribution can modulate meal start and duration.
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Kent R, Bar-Massada A, Carmel Y. Bird and mammal species composition in distinct geographic regions and their relationships with environmental factors across multiple spatial scales. Ecol Evol 2014; 4:1963-71. [PMID: 24963389 PMCID: PMC4063488 DOI: 10.1002/ece3.1072] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2014] [Revised: 03/03/2014] [Accepted: 03/25/2014] [Indexed: 11/16/2022] Open
Abstract
Global patters of species distributions and their underlying mechanisms are a major question in ecology, and the need for multi-scale analyses has been recognized. Previous studies recognized climate, topography, habitat heterogeneity and disturbance as important variables affecting such patterns. Here we report on analyses of species composition – environment relationships among different taxonomic groups in two continents, and the components of such relationships, in the contiguous USA and Australia. We used partial Canonical Correspondence Analysis of occurrence records of mammals and breeding birds from the Global Biodiversity Information Facility, to quantify relationships between species composition and environmental variables in remote geographic regions at multiple spatial scales, with extents ranging from 105 to 107 km2 and sampling grids from 10 to 10,000 km2. We evaluated the concept that two elements contribute to the impact of environmental variables on composition: the strength of species' affinity to an environmental variable, and the amount of variance in the variable. To disentangle these two elements, we analyzed correlations between resulting trends and the amount of variance contained in different environmental variables to isolate the mechanisms behind the observed relationships. We found that climate and land use-land cover are responsible for most explained variance in species composition, regardless of scale, taxonomic group and geographic region. However, the amount of variance in species composition attributed to land use / land cover (LULC) was closely related to the amount of intrinsic variability in LULC in the USA, but not in Australia, while the effect of climate on species composition was negatively correlated to the variability found in the climatic variables. The low variance in climate, compared to LULC, suggests that species in both taxonomic groups have strong affinity to climate, thus it has a strong effect on species distribution and community composition, while the opposite is true for LULC.
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Affiliation(s)
- Rafi Kent
- Department of Plant Sciences, University of Cambridge Downing Street, Cambridge, CB23EA, U.K ; Department of Civil and Environmental Engineering, The Technion - Israel Institute of Technology Haifa, 32000, Israel
| | - Avi Bar-Massada
- Department of Biology and Environment, University of Haifa at Oranim Kiryat Tivon, 36006, Israel
| | - Yohay Carmel
- Department of Civil and Environmental Engineering, The Technion - Israel Institute of Technology Haifa, 32000, Israel
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Benhamou S. Of scales and stationarity in animal movements. Ecol Lett 2013; 17:261-72. [DOI: 10.1111/ele.12225] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Revised: 10/11/2013] [Accepted: 10/30/2013] [Indexed: 12/19/2022]
Affiliation(s)
- Simon Benhamou
- Centre d’Écologie Fonctionnelle et Évolutive; CNRS UMR 5175 Montpellier France
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Maina J, de Moel H, Vermaat JE, Bruggemann JH, Guillaume MMM, Grove CA, Madin JS, Mertz-Kraus R, Zinke J. Linking coral river runoff proxies with climate variability, hydrology and land-use in Madagascar catchments. MARINE POLLUTION BULLETIN 2012; 64:2047-59. [PMID: 22853989 DOI: 10.1016/j.marpolbul.2012.06.027] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2012] [Revised: 06/25/2012] [Accepted: 06/27/2012] [Indexed: 05/21/2023]
Abstract
Understanding the linkages between coastal watersheds and adjacent coral reefs is expected to lead to better coral reef conservation strategies. Our study aims to examine the main predictors of environmental proxies recorded in near shore corals and therefore how linked near shore reefs are to the catchment physical processes. To achieve these, we developed models to simulate hydrology of two watersheds in Madagascar. We examined relationships between environmental proxies derived from massive Porites spp. coral cores (spectral luminescence and barium/calcium ratios), and corresponding time-series (1950-2006) data of hydrology, climate, land use and human population growth. Results suggest regional differences in the main environmental drivers of reef sedimentation: on annual time-scales, precipitation, river flow and sediment load explained the variability in coral proxies of river discharge for the northeast region, while El Niño-Southern Oscillation (ENSO) and temperature (air and sea surface) were the best predictors in the southwest region.
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Affiliation(s)
- Joseph Maina
- Department of Biological Sciences, Macquarie University, Sydney, NSW, Australia.
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Fung T, Seymour RM, Johnson CR. Alternative stable states and phase shifts in coral reefs under anthropogenic stress. Ecology 2011; 92:967-82. [PMID: 21661558 DOI: 10.1890/10-0378.1] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Ecosystems with alternative stable states (ASS) may shift discontinuously from one stable state to another as environmental parameters cross a threshold. Reversal can then be difficult due to hysteresis effects. This contrasts with continuous state changes in response to changing environmental parameters, which are less difficult to reverse. Worldwide degradation of coral reefs, involving "phase shifts" from coral to algal dominance, highlights the pressing need to determine the likelihood of discontinuous phase shifts in coral reefs, in contrast to continuous shifts with no ASS. However, there is little evidence either for or against the existence of ASS for coral reefs. We use dynamic models to investigate the likelihood of continuous and discontinuous phase shifts in coral reefs subject to sustained environmental perturbation by fishing, nutrification, and sedimentation. Our modeling results suggest that coral reefs with or without anthropogenic stress can exhibit ASS, such that discontinuous phase shifts can occur. We also find evidence to support the view that high macroalgal growth rates and low grazing rates on macroalgae favor ASS in coral reefs. Further, our results suggest that the three stressors studied, either alone or in combination, can increase the likelihood of both continuous and discontinuous phase shifts by altering the competitive balance between corals and algae. However, in contrast to continuous phase shifts, we find that discontinuous shifts occur only in model coral reefs with parameter values near the extremes of their empirically determined ranges. This suggests that continuous shifts are more likely than discontinuous shifts in coral reefs. Our results also suggest that, for ecosystems in general, tackling multiple human stressors simultaneously maximizes resilience to phase shifts, ASS, and hysteresis, leading to improvements in ecosystem health and functioning.
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Affiliation(s)
- Tak Fung
- School of Biological Sciences, Queen's University Belfast, Belfast BT9 7BL United Kingdom.
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14
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Padgham M. Relating Climatic Dynamics in Time and Space to Ecological Responses, with Application to Australian Waterbirds. Ecosystems 2010. [DOI: 10.1007/s10021-010-9397-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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15
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Simelane TS. Impacts of traditional land uses on biodiversity outside conservation areas: effects on dung beetle communities of Vaalbos National Park. Afr J Ecol 2009. [DOI: 10.1111/j.1365-2028.2009.01138.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Azovsky AI. Structural complexity of species assemblages and spatial scale of community organization: A case study of marine benthos. ECOLOGICAL COMPLEXITY 2009. [DOI: 10.1016/j.ecocom.2008.12.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Dumont E, Bakker EJ, Bouwman L, Kroeze C, Leemans R, Stein A. A framework to identify appropriate spatial and temporal scales for modeling N flows from watersheds. Ecol Modell 2008. [DOI: 10.1016/j.ecolmodel.2007.10.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Habeeb RL, Johnson CR, Wotherspoon S, Mumby PJ. Optimal scales to observe habitat dynamics: a coral reef example. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2007; 17:641-7. [PMID: 17494384 DOI: 10.1890/06-0348] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
A new technique to estimate the characteristic length scales (CLSs) of real ecological systems provides an objective means to identify the optimal scale(s) of observation to best detect underlying dynamical trends. Application of the technique to natural systems has focused on identifying appropriate scales to measure the dynamics of species as descriptors of community and ecosystem dynamics. However, ecosystem monitoring is often based not on assessing single species, but on species assemblages, functional groups, or habitat types. We asked whether the concept of CLSs based on dynamic interactions among species could be extended to examine interactions among habitat types and thus to identify optimal scales for observing habitat dynamics. A time series of three spatial maps of benthic habitats on a Caribbean coral reef was constructed from aerial photographs, Compact Airborne Spectrographic Imager (CASI) images, and IKONOS satellite images, providing the short time sequence required for this technique. We estimated the CLS based on the dynamics of three distinct habitat types: dense stands of seagrass, sparse stands of seagrass, and Montastrea patch reefs. Despite notable differences in the areal extent of and relative change in these habitats over the 21-year observation period, analyses based on each habitat type indicated a similar CLS of -300 m. We interpret the consistency of CLSs among habitats to indicate that the dynamics of the three habitat types are linked. The results are encouraging, and they indicate that CLS techniques can be used to identify the appropriate scale at which to monitor ecosystem trends on the basis of the dynamics of only one of a disparate suite of habitat types.
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Affiliation(s)
- Rebecca L Habeeb
- School of Zoology and Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, GPO Box 252-05, Hobart, Tasmania 7001, Australia
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Magierowski RH, Johnson CR. Robustness of surrogates of biodiversity in marine benthic communities. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2006; 16:2264-75. [PMID: 17205903 DOI: 10.1890/1051-0761(2006)016[2264:rosobi]2.0.co;2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The usefulness of surrogates to estimate complex variables describing community structure, such as the various components of biodiversity, is long established. Most attention has been given to surrogates of species richness and species diversity and has focused on identifying a subset of taxa as a surrogate of total community richness or diversity. In adopting a surrogate measure, it is assumed that the relationship between the surrogate(s) and total richness or diversity is consistent in both space and time. These assumptions are rarely examined explicitly. We examined the robustness of potential surrogates of familial richness and multivariate community structure for macrofauna communities inhabiting artificial kelp holdfasts by comparing among communities of dissimilar ages and among communities established at different times of the year. This is important because most benthic "landscapes" will be a mosaic of patches reflecting different intensities, frequencies, and timing of disturbances. The total abundance of organisms and familial richness of crustaceans or polychaetes were all good predictors of total familial richness (R2 > 0.68). In contrast, while the familial richness of other groups, such as mollusks and echinoderms, were well correlated with total familial richness for communities at an early stage of development, the strength of these relationships declined with community age. For multivariate community structure, carefully selected subsets of approximately 10% of the total taxa yielded similar patterns to the total suite of taxa, irrespective of the age of the community. Thus, useful surrogates of both familial richness and multivariate community structure can be identified for this type of community. However, the choice of technique for selecting surrogate taxa largely depends on the nature of the pilot data available, and careful selection is required to ensure that surrogates perform consistently across different-aged communities. While the specific taxa selected as surrogates will vary among different communities, and possibly even among similar communities at different sites, the techniques and the concepts we address are applicable to any community type.
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Affiliation(s)
- Regina H Magierowski
- School of Zoology and Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, Private Bag 05, Hobart 7001, Australia
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