Spatial distribution and performance of native and invasive Ardisia (Myrsinaceae) species in Puerto Rico: the anatomy of an invasion

Difference in Germination Traits between Congeneric Native and Exotic Species May Affect Invasion

Germination traits are components of invasion potential, and comparing seed traits in sympatric native and invasive species can offer insights into the invasion process. We characterized seed germination traits and how they influenced the success of Eragrostis mexicana, a native species, and Eragrostis tenuifolia, an exotic species (Poaceae) in Mexico, in the context of their potential for biological invasion. Seeds from both species were collected from four sites in a natural protected area in Mexico City, and the germination of seeds of different ages was conducted in experiments at different temperatures. E. tenuifolia exhibited higher germination percentages than the native E. mexicana across all treatments. Seed age had differential effects, with older seeds of the native E. mexicana germinating better, while E. tenuifolia performed better with younger seeds. Temperature positively impacted germination for both species, although E. mexicana was limited at lower temperatures. Exotic E. tenuifolia can germinate over a wider temperature range with earlier germination rates, and generate a seed bank lasting several years, which may contribute to naturalization. The importance of germination traits in the context of invasive species establishment underscores the potential role of seed banks in facilitating biological invasions.

The phylogeny and global biogeography of Primulaceae based on high-throughput DNA sequence data

The angiosperm family Primulaceae is morphologically diverse and distributed nearly worldwide. However, phylogenetic uncertainty has obstructed the identification of major morphological and biogeographic transitions within the clade. We used target capture sequencing with the Angiosperms353 probes, taxon-sampling encompassing nearly all genera of the family, tree-based sequence curation, and multiple phylogenetic approaches to investigate the major clades of Primulaceae and their relationship to other Ericales. We generated dated phylogenetic trees and conducted broad-scale biogeographic analyses as well as stochastic character mapping of growth habit. We show that Ardisia, a pantropical genus and the largest in the family, is not monophyletic, with at least 19 smaller genera nested within it. Neotropical members of Ardisia and several smaller genera form a clade, an ancestor of which arrived in the Neotropics and began diversifying about 20 Ma. This Neotropical clade is most closely related to Elingamita and Tapeinosperma, which are most diverse on islands of the Pacific. Both Androsace and Primula are non-monophyletic by the inclusion of smaller genera. Ancestral state reconstructions revealed that there have either been parallel transitions to an herbaceous habit in Primuloideae, Samolus, and at least three lineages of Myrsinoideae, or a common ancestor of nearly all Primulaceae was herbaceous. Our results provide a robust estimate of phylogenetic relationships across Primulaceae and show that a revised classification of Myrsinoideae and several other clades within the family is necessary to render all genera monophyletic.

Differential germination strategies of native and introduced populations of the invasive species Plantago virginica

Germination strategies are critically important for the survival, establishment and spread of plant species. Although many plant traits related to invasiveness have been broadly studied, the earliest part of the life cycle, germination, has received relatively little attention. Here, we compared the germination patterns between native (North America) and introduced (China) populations of Plantagovirginica for four consecutive years to examine whether there has been adaptive differentiation in germination traits and how these traits are related to local climatic conditions. We found that the introduced populations of P.virginica had significantly higher germination percentages and faster and shorter durations of germination than native populations. Critically, the native populations had a significantly larger proportion of seeds that stayed dormant in all four years, with only 60% of seeds germinating in year 1 (compared to >95% in introduced populations). These results demonstrate striking differences in germination strategies between native and introduced populations which may contribute to their successful invasion. Moreover, the germination strategy of P.virginica in their native range exhibited clear geographical variation across populations, with trends towards higher germination percentages at higher latitudes and lower annual mean temperatures and annual precipitation. In the introduced range, however, their germination strategies were more conserved, with less variation amongst populations, suggesting that P.virginica may have experienced strong selection for earlier life history characteristics. Our findings highlight the need to examine the role of rapid evolution of germination traits in facilitating plant invasion.

Potential Germination Success of Exotic and Native Trees Coexisting in Central Spain Riparian Forests

We compared potential germination success (i.e., percentage of produced seeds that germinate under optimal conditions), the percentage of empty and insect-damaged seeds, germinability (Gmax), and time to germination (Tgerm) between the exoticsAilanthus altissima,Robinia pseudoacacia,andUlmus pumilaand two coexisting native trees (Fraxinus angustifoliaandUlmus minor) in the riparian forests of Central Spain. Additionally, we tested the effect of seed age, seed bank type (canopy or soil) and population onGmaxandTgermofA. altissimaandR. pseudoacacia, which are seed-banking species. Species ranked by their potential germination success wereA. altissima>U. pumila>R. pseudoacacia>U. minor>F. angustifolia. The combination of a highGmaxand negligible seed insect-damage providedA. altissimawith a potential germination advantage over the natives, which were the least successful due to an extremely high percentage of empty seeds or a very lowGmax.R. pseudoacaciashowed high vulnerability to insect seed predation which might be compensated with the maintenance of persistent seed banks with highGmax.GmaxandTgermwere strongly affected by seed age in the seed-banking invaders, but between-seed bank variation ofGmaxandTgermdid not show a consistent pattern across species and populations.

Preference of a native beetle for "exoticism," characteristics that contribute to invasive success of Costelytra zealandica (Scarabaeidae: Melolonthinae)

Widespread replacement of native ecosystems by productive land sometimes results in the outbreak of a native species. In New Zealand, the introduction of exotic pastoral plants has resulted in diet alteration of the native coleopteran species, Costelytra zealandica (White) (Scarabaeidae) such that this insect has reached the status of pest. In contrast, C. brunneum (Broun), a congeneric species, has not developed such a relationship with these ‘novel’ host plants. This study investigated the feeding preferences and fitness performance of these two closely related scarab beetles to increase fundamental knowledge about the mechanisms responsible for the development of invasive characteristics in native insects. To this end, the feeding preference of third instar larvae of both Costelytra species was investigated using an olfactometer device, and the survival and larval growth of the invasive species C. zealandica were compared on native and exotic host plants. Costelytra zealandica, when sampled from exotic pastures, was unable to fully utilise its ancestral native host and showed higher feeding preference and performance on exotic plants. In contrast, C. zealandica sampled from native grasslands did not perform significantly better on either host and showed similar feeding preferences to C. brunneum, which exhibited no feeding preference. This study suggests the possibility of strong intraspecific variation in the ability of C. zealandica to exploit native or exotic plants, supporting the hypothesis that such ability underpins the existence of distinct host-races in this species.

Positive frequency dependence undermines the success of restoration using historical disturbance regimes

Anthropogenic alterations of historical disturbance regimes (e.g. suppressing floods and wildfires) is a primary mechanism by which exotic species can come to dominate native communities. Unfortunately, reinstating historical disturbance regimes to restore native communities has achieved mixed success. The presence of positive frequency dependence (PFD) is commonly invoked to explain why exotic plant invasions are so difficult to eradicate. However, models examining PFD have not considered the effect of reintroducing disturbances. Using a spatially explicit individual-based model, we consider how magnitude and direction of frequency dependence of native and exotic species affects the success of reintroducing disturbances that favour fitness of natives over exotics. Our model illustrates why restoration is difficult; there is a narrow range of parameters that allows for native species to eliminate or coexist with exotics once they have established. Dominance by exotic invaders occurs with moderate initial frequencies of exotic individuals, aggregation of these individuals, or an exotic propagule production advantage. Reintroducing disturbances allows native dominance only when PFD of the exotic is weaker than that of the native species, disturbance intervals are short, and/or exotics are not initially frequent. Our framework provides guidelines for conditions in which the reintroduction of disturbances will effectively restore invaded habitats.