Soil disturbance effects on the composition of seed-dispersing ants in roadside environments

Myrmecochory (the dispersal of seeds by ants) is a significant ecological process in sclerophyll woodlands, but habitat disturbance is known to alter the extent and success of this mutualism. We investigated the influence of soil disturbance on the composition of the seed-dispersing ant community. Surveys were conducted in roadside verges where soils are regularly disturbed by road maintenance activities. Using a ‘cafeteria’ bait station approach, we selected 24 roads of different widths to investigate ant composition and abundance in relation to soil disturbance. We found ant species richness was greater in non-disturbed than disturbed zones, where road verge width significantly influenced results. The composition and abundance of individual seed-dispersing ant species varied between disturbed and non-disturbed zones. Rhytidoponera metallica were more abundant in non-disturbed sites, whereas Melophorus bruneus and Monomorium rothseini were more frequently recorded in disturbed areas. Commonly found Iridomyrmex purpureus was significantly more abundant in disturbed zones in narrow roadsides and vice versa in wide roadsides, and strongly influenced total community composition. Variation in the abundance of commonly recorded Iridomyrmex and Monomorium genera were related more to site conditions (roadside width and habitat) than soil disturbance. The rich composition of seed dispersing ants in roadside environments, and the effects of soil disturbances on these ant communities that we describe, provide a key insight to important seed dispersal vectors occurring in fragmented rural landscapes.     

How human disturbance of tropical rainforest can influence avian fruit removal

Fruit consumption by birds is an important ecological interaction that contributes to seed dispersal in tropical rainforests. In this field experiment, we asked whether moderate human disturbance alters patterns of avian frugivory: we measured fruit removal by birds in the lower montane rainforest of Tobago, West Indies, using artificial infructescences made with natural fruits from two common woody plants of the forest understory (Psychotria spp., Rubiaceae). Displays were mounted simultaneously in three forest habitats chosen to represent a gradient of increasing habitat disturbance (primary, intermediate and disturbed), caused by subsistence land use adjacent to a protected forest reserve. We measured the numbers of fruits removed and the effect of fruit position on the likelihood of removal, along with the abundances of all fruits and fruit‐eating birds at the study sites. Fruit removal was highly variable and there was not a significant difference in removal rate among forest habitats; however, the trend was for higher rates of removal from displays in primary forest. Canopy cover, natural fruit availability, and frugivore abundance were not good predictors of fruit removal. Birds preferred more accessible fruits (those proximal to the perch) in all habitats, but in disturbed forest, there was a tendency for distal fruits to be chosen more frequently than in the other forest types. One possible explanation for this pattern is that birds in disturbed forests were larger than those in other habitats, and hence were better able to reach the distal fruits. Coupled with differences in bird community composition among the forest types, this suggests that different suites of birds were removing fruit in primary versus disturbed forest. As frugivore species have different effectiveness as seed dispersers, the among‐habitat differences in fruit removal patterns that we observed could have important implications for plant species experiencing disturbance; these possible implications include altered amounts of seed deposition and seedling recruitment in Tobago's tropical rainforest.     

Forest disturbance and seasonal food availability influence a conditional seed dispersal mutualism

The interaction between granivorous scatterhoarding mammals and plants is a conditional mutualism: scatterhoarders consume seeds (acting as predators), but the movement of seed by scatterhoarders may contribute to dispersal (acting as mutualists). Understanding the ecological factors that shape this relationship is highly relevant in anthropogenically disturbed tropical forests where large‐bodied frugivores are extirpated. In such forests, large‐seeded trees that once depended on these frugivores for dispersal may now only have scatterhoarders as prospective dispersers. We studied Carapa oreophila (Meliaceae) in an Afromontane forest, to test the hypotheses that the proportion of seeds immediately consumed or hoarded (dispersed) would vary over a disturbance gradient. Temporal replication also afforded exploration of how habitat effects might vary with food availability. Using a Bayesian framework, we demonstrate that seeds were more likely to be hoarded in less disturbed forest, irrespective of temporal variation in food abundance. In contrast, forest disturbance only appeared to increase seed predation in temporal replicates that coincided with sustained food availability. These results highlight the potential variability in the dynamics between plants and scatterhoarders over fine temporal scales, elucidating possible ecological scenarios where scatterhoarders might act as mutualists (contributing positively to plant recruitment). Our study also fills important knowledge gaps about the importance of scatterhoarders as dispersers in tropical forests depleted of large‐bodied frugivores, particularly in Africa where scatterhoarding mutualisms have not been extensively studied.     

Environmental heterogeneity and interspecific interactions influence nest occupancy by key seed-dispersing ants

The complex interplay between species along environmental gradients ultimately shapes their distributions and additional community interactions. Ant-mediated seed dispersal fails in the wettest habitat of deciduous forest in eastern North America, and we examine whether this pattern corresponds with colony distributions for seed-dispersing ants and associated heterogeneity in abiotic and biotic variables. Specifically, we used spatial variation in soil moisture, temperature and diffuse light along natural habitat gradients and experimentally manipulated soil moisture gradients to examine ant habitat selection. We also examined niche segregation between effective (Aphaenogaster spp.) and ineffective (Lasius alienus Foerster) seed-dispersing ants across these environmental gradients. Whereas most research links ant foraging and nesting with temperature gradients, we find niche segregation between Aphaenogaster spp. and L. alienus by soil moisture along naturally occurring gradients and in experimentally irrigated upland habitat. The failure of Aphaenogaster spp. to occupy the wettest habitats, where L. alienus is present, is consistent with observed seed dispersal failure in these habitats. These results indicate that environmental heterogeneity drives niche segregation between effective (Aphaenogaster spp.) and ineffective (L. alienus) seed dispersers so each occupies distinct habitat. Most forest understory plants rely on ants for seed dispersal. Our research implies that climate-mediated interactions between effective and ineffective seed dispersing ant species may structure the microhabitat distributions for woodland herbs.     

Lowland tapirs facilitate seed dispersal in degraded Amazonian forests

The forests of southeastern Amazonia are highly threatened by disturbances such as fragmentation, understory fires, and extreme climatic events. Large‐bodied frugivores such as the lowland tapir (Tapirus terrestris) have the potential to offset this process, supporting natural forest regeneration by dispersing a variety of seeds over long distances to disturbed forests. However, we know little about their effectiveness as seed dispersers in degraded forest landscapes. Here, we investigate the seed dispersal function of lowland tapirs in Amazonian forests subject to a range of human (fire and fragmentation) and natural (extreme droughts and windstorms) disturbances, using a combination of field observations, camera traps, and light detection and ranging (LiDAR) data. Tapirs travel and defecate more often in degraded forests, dispersing much more seeds in these areas [9,822 seeds per ha/year (CI_95% = 9,106; 11,838)] than in undisturbed forests [2,950 seeds per ha/year (CI_95% = 2,961; 3,771)]. By effectively dispersing seeds across disturbed forests, tapirs may contribute to natural forest regeneration—the cheapest and usually the most feasible way to achieve large‐scale restoration of tropical forests. Through the dispersal of large‐seeded species that eventually become large trees, such frugivores also contribute indirectly to maintaining forest carbon stocks. These functions may be critical in helping tropical countries to achieve their goals to maintain and restore biodiversity and its ecosystem services. Ultimately, preserving these animals along with their habitats may help in the process of natural recovery of degraded forests throughout the tropics. Abstract in Portuguese is available with online material.     

Reduced dispersal at nonexpanding range margins: A matter of disperser identity

The evolution of dispersal at range margins received much attention recently, especially in the context of dynamic range shifts, such as those following climate change. However, much less attention has been devoted to study variation in and selection on dispersal at nonexpanding range margins, where populations are often small and isolated, and empirical test is dearly missing. To fill this gap, we tested whether dispersal of an ant‐dispersed perennial plant (Sternbergia clusiana) is quantitatively and/or qualitatively reduced toward a nonexpanding range margin. We evaluated plant investment in dispersal structures (elaiosome), seed removal rates, and the relative abundance, activity, and behavior of low‐ and high‐quality seed‐dispersing ants in six sites ranging from mesic Mediterranean site to arid site (>600 to <100 mm of annual rainfall, respectively), which marks the southern range margin of the species. In a set of cafeteria and baiting experiments, we found that overall seed removal rates, the contribution of high‐quality dispersers, maximum dispersal distance and dispersal‐conducive ant behavior decreased toward range margins. These findings agree with a lower investment in reward by range margin plant populations, as reflected by lower elaiosome/seed ratio, but not by variation in the reward chemistry. More than variation in traits controlled by the plants, the variation in ant–seed interactions could be attributed to reduced presence and activity of the more efficient seed‐dispersing ants in the marginal populations. Specifically, we found a mismatch between local distribution of potentially effective seed dispersers and that of the plant, even though those dispersers were observed in the study site. Interestingly, although the observed variation in the outcome of ant–seed interactions supported the prediction of reduced dispersal at nonexpanding range margins with small and isolated populations, the underlying mechanism seems to be incidental difference in the seed‐dispersing ant community rather than a plant‐mediated response to selection.     

Dung Beetle Communities and Seed Dispersal in Primary Forest and Disturbed Land in Amazonia1

Seeds from tropical fruiting trees ingested and defecated on the soil surface by primary dispersers (such as primates) are vulnerable to destruction from rodents, insects, and fungi. Burial by dung beedes as an incidental result of their feeding and nesting activities often provides these seeds with refugia from attack. To examine the effect of habitat disturbance on the dung beetle communities involved in this process, I surveyed dung beedes at three sites in the Amazon basin, in die states of Parí, Amazonas, and Rondónia, Brazil. Through principal component analysis on measurements of size and behavioral characters of beedes, I determined the relative quality of beetle species as seed dispersers (dispersal defined as horizontal or vertical movement of seeds) and ranked them into seed dispersal guilds. I used correspondence analysis to examine in what habitats (primary forest or varying degrees of disturbed habitat) these guilds were abundant. Most guilds decreased with increasing habitat disturbance, but one guild made up of large nocturnal burrowers (primarily Dichotomius) became more abundant with increasing disturbance (up to the level of highest disturbance surveyed), at which point all dung beede species became scarce. Clear–cuts had lower species richness, lower abundance, and lower biomass dian forested areas. These results imply that clear–cutting is detrimental to all seed dispersal dynamics in tropical rain forests, but that some levels of disturbance allow enough disperser activity to preserve this ecosystem function.     

Primate and Dung Beetle Communities in Secondary Growth Rain Forests: Implications for Conservation of Seed Dispersal Systems

Conservation efforts are often aimed at one or a few species. However, habitat sustainability relies on ecological interactions among species, such as seed dispersal. Thus, a community-scale conservation strategy may be more valuable in some settings. We describe communities of primary (primates) and secondary (dung beetles) seed dispersers from 5 sites in the Brazilian Amazon. We estimate community biomass of these taxa and, using multivariate ordination, examine the potential for natural reforestation at each site, given the communities of seed dispersers present. Since disturbed habitat is increasingly common and increasingly the focus of conservation efforts, we also examine differences among seed disperser communities between primary forest and secondary growth at each site. Analyses of faunal biomass in different localities and habitats indicate that secondary growth receives nearly as much use by primates as primary forest; given the dominant groups of dung beetles in secondary growth, disturbed habitat should show a pattern of seed burial that is clumped and deep. Areas with high biomass of Alouatta spp. and the large nocturnal dung beetle species may have the greatest potential for natural reforestation of secondary growth particularly for large seeded species. The data suggest that knowledge of the biomass of primary and secondary dispersing fauna facilitates predictions for the likelihood of disturbed habitat to regenerate and comparisons of sites in broader geographical areas e.g., Neotropical vs. Paleotropical forests.     

Fishing‐down within populations harms seed dispersal mutualism

Large fish are often the most effective seed dispersers, but they are also the preferred target for fisheries. We recently started to comprehend the detrimental impacts of the extirpation of large frugivorous fish species on natural forest regeneration, but we lack a general understanding of how intraspecific size‐selective harvest affects fish–fruit mutualism. Our literature review demonstrated that large individuals within populations positively affect diverse aspects of seed dispersal, from consuming a higher diversity of seeds to enhancing germination. Furthermore, we filled a research gap by studying how individual size variations within two small frugivorous fish species (<16 cm) affect seed dispersal in flooded savannas. Even within small‐bodied species, large individuals swallow a higher number of intact seeds, but not necessarily a higher proportion. Overall, our results demonstrate the disproportional role of large‐bodied individuals as key seed dispersers in flooded habitats. Consequently, fishing‐down within both large‐ and small‐bodied species can negatively affect seed dispersal and natural regeneration in overfished wetlands.     

Fragmentation, habitat composition and the dispersal/predation balance in interactions between the Mediterranean myrtle and avian frugivores

Human‐induced fragmentation and disturbance of natural habitats can shift abundance and composition of frugivore assemblages, which may alter patterns of frugivory and seed dispersal. However, despite their relevance to the functioning of ecosystems, plant‐frugivore interactions in fragmented areas have been to date poorly studied. I investigated spatial variation of avian frugivore assemblages and fruit removal by dispersers and predators from Mediterranean myrtle shrubs (Myrtus communis) in relation to the degree of fragmentation and habitat features of nine woodland patches (72 plants). The study was conducted within the chronically fragmented landscape of the Guadalquivir Valley (SW Spain), characterized by ~1% of woodland cover. Results showed that the abundance and composition of the disperser guild was not affected by fragmentation, habitat features or geographical location. However, individual species and groups of resident/migrant birds responded differently: whereas resident dispersers were more abundant in large patches, wintering dispersers were more abundant in fruit‐rich patches. Predator abundances were similar between patches, although the guild composition shifted with fragmentation. The proportion of myrtle fruits consumed by dispersers and predators varied greatly between patches, but did not depend on bird abundances. The geographical location of patches determined the presence or absence of interactions between myrtles and seed predators (six predated and three non‐predated patches), a fact that greatly influenced fruit dispersal success. Moreover, predation rates were lower (and dispersal rates higher) in large patches with fruit‐poor heterospecific environments (i.e. dominated by myrtle). Predator satiation and a higher preference for heterospecific fruits by dispersers may explain these patterns. These results show that 1) the frugivore assemblage in warm Mediterranean lowlands is mostly composed of fragmentation‐tolerant species that respond differently to landscape changes; and 2) that the feeding behaviour of both dispersers and predators influenced by local fruit availability may be of great importance for interpreting patterns of frugivory throughout the study area.     

Impact of habitat structure and fruit abundance on avian seed dispersal and fruit predation

So far, it is poorly understood how differential responses of avian seed dispersers and fruit predators to changes in habitat structure and fruit abundance along land-use gradients may translate into consequences for the seed dispersal of associated plants. We selected a gradient of habitat modification (forest, semi-natural, and rural habitat) characterized by decreasing tree cover and a high variation in local fruit availability. Along this gradient we quantified fruit removal by avian seed dispersers and fruit predators from 18 Sorbus aucuparia trees. We analyzed the relative importance of tree cover and fruit abundance in explaining species richness, abundance and fruit removal rates of both guilds from S. aucuparia trees. Species richness and abundance of seed dispersers decreased with decreasing tree cover, whereas fruit removal by seed dispersers decreased with decreasing fruit abundance independent of tree cover. Both variables had no effect on species richness, abundance and fruit removal by fruit predators. Consequently, seed dispersers dominated relative fruit removal in fruit-rich sites but the dispersal/predation ratio shifted in favor of predation in fruit-poor habitat patches. Our study demonstrates that variation in local habitat structure and fruit abundance can cause guild-specific responses. Such responses may result in a shift in fruit removal regimes and might affect the dispersal ability of dependent fruiting plants. Future studies should aim at possible consequences for plant recruitment and guild-specific responses of frugivores to disturbance gradients on the level of entire plant–frugivore associations.     

The future distribution of river fish: The complex interplay of climate and land use changes,species dispersal and movement barriers

The future distribution of river fishes will be jointly affected by climate and land use changes forcing species to move in space. However, little is known whether fish species will be able to keep pace with predicted climate and land use‐driven habitat shifts, in particular in fragmented river networks. In this study, we coupled species distribution models (stepwise boosted regression trees) of 17 fish species with species‐specific models of their dispersal (fish dispersal model FIDIMO) in the European River Elbe catchment. We quantified (i) the extent and direction (up‐ vs. downstream) of predicted habitat shifts under coupled “moderate” and “severe” climate and land use change scenarios for 2050, and (ii) the dispersal abilities of fishes to track predicted habitat shifts while explicitly considering movement barriers (e.g., weirs, dams). Our results revealed median net losses of suitable habitats of 24 and 94 river kilometers per species for the moderate and severe future scenarios, respectively. Predicted habitat gains and losses and the direction of habitat shifts were highly variable among species. Habitat gains were negatively related to fish body size, i.e., suitable habitats were projected to expand for smaller‐bodied fishes and to contract for larger‐bodied fishes. Moreover, habitats of lowland fish species were predicted to shift downstream, whereas those of headwater species showed upstream shifts. The dispersal model indicated that suitable habitats are likely to shift faster than species might disperse. In particular, smaller‐bodied fish (<200 mm) seem most vulnerable and least able to track future environmental change as their habitat shifted most and they are typically weaker dispersers. Furthermore, fishes and particularly larger‐bodied species might substantially be restricted by movement barriers to respond to predicted climate and land use changes, while smaller‐bodied species are rather restricted by their specific dispersal ability.     

Life history variation across a riverine landscape: intermediate levels of disturbance favor sexual reproduction in the ant‐dispersed herb Ranunculus ficaria

Global climate change can fundamentally alter disturbance regimes across landscapes, but little is known about how species adjust their life histories to shifts in disturbance regimes. In plants, dispersal by seeds may permit rapid re‐colonization under frequent disturbances, but often seed‐dispersing animals may be absent and local dispersal by vegetative diaspores may be a more efficient means of occupying open space in the vicinity of the plant. We tested the effect of disturbances due to inundation on the investment in seed production by the ant‐dispersed plant, Ranunculus ficaria ssp. bulbifer. During seed ripening we collected 392 plants within a landscape mosaic of 39 sites with different levels of inundation. We measured the mass of fruits and other tissues (leafs, roots, bulbils, stalks) and described plant growth form. We found that fruit numbers and masses were more variable among plants than numbers and masses of other tissues. We then standardized fruit mass against the mass of other tissues and other growth‐form parameters. Standardized fruit mass showed a highly significantly hump‐shaped relationship with the level of inundation disturbances. This pattern was consistent across 12 small‐scale transects and thus not confounded by spatial autocorrelation within landscapes. The pattern was also confirmed by analyses that simultaneously accounted for disturbance and morphological co‐variables. We thus conclude that plants invested most heavily into reproduction by seeds under intermediate levels of disturbance. Under intermediate disturbance, seeds are beneficial for rapidly re‐colonizing open space after disturbance while the seed‐dispersers are still available. The life history of mutualists such as ant‐dispersed plants and ants may thus change across a landscape, reflecting small‐scale variation in the disturbance regime.     

Increased propensity for aerial dispersal in disturbed habitats due to intraspecific variation and species turnover

Animal dispersal depends on multiple factors, such as habitat features and life‐history traits of the species. We studied the propensity for ballooning dispersal in spiders under standardized laboratory conditions. The 1269 tested individuals belonged to 124 species and originated from 16 sites with wide variation in habitat type. Spiders from disturbed habitats ballooned 5.5 times more than spiders from stable habitats. In Meioneta rurestris , for which we had enough data for a single‐species analysis, individuals were most dispersive if they originated from highly disturbed habitats. While the data for the other species were not sufficient for single‐species analyses, a hierarchical model that included the data simultaneously on all species suggested that dispersal propensity generally increases within species with the level of habitat disturbance. Dispersal probability showed a trend to increase with niche width, but the higher commonness of species with wide niches provides an alternative explanation for this pattern. As the prevalence of especially dispersive species was highest in disturbed habitats, variation in dispersal propensity was influenced by both inter‐ and intraspecific factors. We conclude that the positive correlation between niche width and dispersal propensity enables generalist species to utilize highly disturbed habitats, whereas the persistence of specialist species with restricted dispersal ability requires the conservation of stable habitats.     

Impact of seed abundance on seed processing and dispersal by the red ant Myrmica rubra

1. Myrmecochory sensu stricto is an ant–plant mutualism in which non‐granivorous ants disperse plant diaspores after feeding on their nutrient‐rich seed appendage, the elaiosome. Phenological traits associated with the diaspore can influence the behaviour of ants and thus their ultimate efficiency as seed dispersers. 2. This study investigated how a contrasting availability of seeds (20 vs. 200 seeds) from the diplochorous Chelidonium majus (Papaveraceae, Linnaeus) plant species influences the behaviour of Myrmica rubra (Formicidae, Linnaeus) ants, from the retrieval of seeds until their dispersal outside the ant nest. 3. Regardless of seed abundance, the ants collected the first diaspores at similar rates. Then, seed retrieval sped up over time for large seed sources until satiation took place with only one‐third of the tested colonies wholly depleting abundant seed sources. 4. No active recruitment by trail‐laying ants was triggered, even to an abundant seed source 5. In both conditions of seed abundance, the majority of the diaspores retrieved inside the nest were discarded with the elaiosome removed and were dispersed at similar distances from the nest. 6. The paper concludes with a discussion of how the quantity of seeds released by a plant with a dual mode of dispersal can potentially influence the behaviour of ant dispersers and hence the dispersal efficiency derived from myrmecochory.     

Land‐use change and the ecological consequences of personality in small mammals

Many plants rely on animals for seed dispersal, but are all individuals equally effective at dispersing seeds? If not, then the loss of certain individual dispersers from populations could have cascade effects on ecosystems. Despite the importance of seed dispersal for forest ecosystems, variation among individual dispersers and whether land‐use change interferes with this process remains untested. Through a large‐scale field experiment conducted on small mammal seed dispersers, we show that an individual's personality affects its choice of seeds, as well as how distant and where seeds are cached. We also show that anthropogenic habitat modifications shift the distribution of personalities within a population, by increasing the proportion of bold, active, and anxious individuals and in‐turn affecting the potential survival and dispersal of seeds. We demonstrate that preserving diverse personality types within a population is critical for maintaining the key ecosystem function of seed dispersal.     

Seed Dispersal by Primates in Asian Habitats: From Species,to Communities,to Conservation

Primates are among the most important seed dispersers in the habitats they occupy. Understanding the extent of, and gaps in, our knowledge of seed dispersal by Asian primates is essential, because many of these primates are extremely vulnerable to anthropogenic disturbance. In this review, I show how initial studies focused on the role of individual species in seed dispersal have expanded more recently to consider their role in the wider frugivore community. There are five functional groups of primate seed dispersers in Asia; most of our information comes from the (usually) highly frugivorous macaques and gibbons, while our understanding of the roles played by orangutans and, especially, colobines and lorises remains rudimentary. Preliminary community-wide studies suggest a pivotal role for gibbons and macaques in frugivore communities, with higher dispersal overlap with other mammals than with birds. The gaps in our knowledge are plentiful, however, including understanding fruit selection in detail, determining how seed dispersal roles might change across different habitats, evaluating the balance between mutualisms and antagonisms in orangutans and macaques, describing postdispersal processes, and documenting how habitats are impacted by changes in primate abundance and behavior.     

Inter‐group variability in seed dispersal by white‐handed gibbons in mosaic forest

Seed dispersers, like white‐handed gibbons (Hylobates lar), can display wide inter‐group variability in response to distribution and abundance of resources in their habitat. In different home ranges, they can modify their movement patterns along with the shape and scale of seed shadow produced. However, the effect of inter‐group variability on the destination of dispersed seeds is still poorly explained. In this study, we evaluate how seed dispersal patterns of this arboreal territorial frugivore varies between two neighboring groups, one inhabiting high quality evergreen forest and one inhabiting low quality mosaic forest. We predicted a difference in seed dispersal distance between the two groups (longer in the poor quality forest). We hypothesized that this difference would be explained by differences in home range size, daily path length, and ranging tortuosity. After 6 months of data collection, the evergreen group had a smaller home range (12.4 ha) than the mosaic group (20.9 ha), significantly longer daily path lengths (1507 m vs. 1114 m respectively) and greater tortuosity (39.1 vs. 16.1 respectively). Using gut passage times and displacement rates, we estimated the median seed dispersal distance as 163 m for the evergreen group (high quality forest) and of 116 m for the mosaic group (low quality forest). This contradiction with our initial prediction can be explained in term of social context, resource distribution, and habitat quality. Our results indicate that gibbons are dispersers of seeds between habitats and that dispersal distances provided by gibbons are influenced by a range of factors, including habitat and social context.     

Impacts of the invasive Argentine ant on native ants and other invertebrates in coastal scrub in south‐eastern Australia

Invasive ants threaten native biodiversity and ecosystem function worldwide. Although their principal direct impact is usually the displacement of native ants, they may also affect other invertebrates. The Argentine ant, Linepithema humile (Dolichoderinae), one of the most widespread invasive ant species, has invaded native habitat where it abuts peri‐urban development in coastal Victoria in south‐eastern Australia. Here we infer impacts of the Argentine ant on native ants and other litter and ground‐dwelling invertebrates by comparing their abundance and taxonomic composition in coastal scrub forest either invaded or uninvaded by the Argentine ant. Species composition of native ants at bait stations and extracted from litter differed significantly between Argentine ant‐invaded and uninvaded sites and this was consistent across years. Argentine ants had a strong effect on epigeic ants, which were either displaced or reduced in abundance. The native ant Rhytidoponera victoriae (Ponerinae), numerically dominant at uninvaded sites, was completely absent from sites invaded by the Argentine ant. However, small hypogeic ants, including Solenopsis sp. (Myrmicinae) and Heteroponera imbellis (Heteroponerinae), were little affected. Linepithema humile had no detectable effect upon the abundance and richness of other litter invertebrates. However, invertebrate group composition differed significantly between invaded and uninvaded sites, owing to the varied response of several influential groups (e.g. Collembola and Acarina). Floristics, habitat structure and measured environmental factors did not differ significantly between sites either invaded or uninvaded by Argentine ants, supporting the contention that differences in native ant abundance and species composition are related to invasion. Changes in the native ant community wrought by Argentine ant invasion have important implications for invertebrate communities in southern Australia and may affect key processes, including seed dispersal.     

Regional zooplankton dispersal provides spatial insurance for ecosystem function

Changing environmental conditions are affecting diversity and ecosystem function globally. Theory suggests that dispersal from a regional species pool may buffer against changes in local community diversity and ecosystem function after a disturbance through the establishment of functionally redundant tolerant species. The spatial insurance provided by dispersal may decrease through time after environmental change as the local community monopolizes resources and reduces community invasibility. To test for evidence of the spatial insurance hypothesis and to determine the role dispersal timing plays in this response we conducted a field experiment using crustacean zooplankton communities in a subarctic region that is expected to be highly impacted by climate change – Churchill, Canada. Three experiments were conducted where nutrients, salt, and dispersal were manipulated. The three experiments differed in time‐since‐disturbance that the dispersers were added. We found that coarse measures of diversity (i.e. species richness, evenness, and Shannon–Weiner diversity) were generally resistant to large magnitude disturbances, and that dispersal had the most impact on diversity when dispersers were added shortly after disturbance. Ecosystem functioning (chl‐a) was degraded in disturbed communities, but dispersal recovered ecosystem function to undisturbed levels. This spatial insurance for ecosystem function was mediated through changes in community composition and the relative abundance of functional groups. Results suggest that regional diversity and habitat connectivity will be important in the future to maintain ecosystem function by introducing functionally redundant species to promote compensatory dynamics.