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Plant Assemblages (plant + assemblage)
Selected AbstractsThe ecological barriers to the recovery of bridal creeper (Asparagus asparagoides (L.) Druce) infested sites: Impacts on vegetation and the potential increase in other exotic speciesAUSTRAL ECOLOGY, Issue 6 2008PETER J. TURNER Abstract To protect native biodiversity from environmental weeds, the impacts that these weeds cause need to be known before weed control commences. Asparagus asparagoides (L.) Druce (bridal creeper) (Asparagaceae) is a serious environmental weed and has been selected for biological control in Australia. To predict the responses of plant communities to the control of bridal creeper, a prerelease baseline of the impacts of bridal creeper on native plant communities was undertaken. Plant assemblages in areas invaded by bridal creeper were compared with reference areas that contained little or no bridal creeper. Areas invaded by bridal creeper contained 52% fewer native plant species when compared with nearby reference areas. However, there was no difference in the number of other exotic plant species between areas. Similar trends were found for the germinable seed bank. Although a greater number of exotic species were present in the seed bank compared with the vegetation surveys, there was still no difference between areas with and without bridal creeper. In a glasshouse trial, exotic species germinated more frequently compared with native species. This could indicate that as bridal creeper density decreases following control, exotic species have an advantage over native species when colonizing areas left vacant by bridal creeper. Second, as bridal creeper areas contained reduced native species richness and cover, they may be susceptible to further weed invasion after bridal creeper is removed. Therefore, simply reducing the presence of bridal creeper may not guarantee successful restoration of invaded areas and additional restoration efforts will be needed to ensure the ultimate goal of protecting native biodiversity is reached. [source] Reproductive interactions mediated by flowering overlap in a temperate hummingbird,plant assemblageOIKOS, Issue 4 2010Marcelo A. Aizen Pollinator-mediated competition through shared pollinators can lead to segregated flowering phenologies, but empirical evidence for the process responsible for this flowering pattern is sparse. During two flowering seasons, we examined whether increasing overlap in flowering phenology decreased conspecific pollination, increased heterospecific pollination, and depressed seed output in the seven species composing a hummingbird,plant assemblage from the temperate forest of southern South America. Overall trends were summarized using meta-analysis. Despite prevailing negative associations, relations between phenological overlap and conspecific pollen receipt varied extensively among species and between years. Heterospecific pollen receipt was low and presumably of limited biological significance. However, our results supported the hypothesis that concurrent flowering promotes interspecific pollen transfer, after accounting for changes in the abundance of conspecific flowers. Seed output was consistently reduced during maximum phenological overlap during the first flowering season because of limited fruit set. Responses varied more during the second year, despite an overall negative trend among species. Relations between estimated effects of phenological overlap on pollination and seed output, however, provided mixed evidence that conspecific pollen loss during pollinator visits to foreign flowers increases pollen limitation. By flowering together, different plant species might benefit each other's pollination by increasing hummingbird recruitment at the landscape level. Nevertheless, our results are mostly consistent with the hypothesis of pollinator-mediated competition shaping the segregated flowering pattern reported previously for this temperate plant assemblage. The mechanisms likely involve effects on male function, whereby pollen-transport loss during heterospecific flower visits limit pollen export, and more variable effects on female function through pollen limitation. [source] Stream order controls geomorphic heterogeneity and plant distribution in a savanna landscapeAUSTRAL ECOLOGY, Issue 2 2009LESEGO KHOMO Abstract We posed the question: does viewing a savanna as a network of streams linked to a matrix of terrestrial hillslopes provide a useful framework to research and understand plant distribution in these landscapes? Our study area, the Phugwane River network, lies in the semi-arid savanna of Kruger National Park, South Africa. We examined changes in hillslope geomorphology from first-, third- and fifth-order hillslopes with regression equations. The distribution of geomorphic boundaries was enumerated by moving window analysis and the relationship between geomorphology and plant distribution was explored through ordination. First-order hillslopes had a simple geomorphology, fewer geomorphic boundaries and a relatively homogeneous plant assemblage. By contrast, fifth-order hillslopes were more complex in geomorphology, with more boundaries and a relatively heterogeneous vegetation pattern. Stream order classification of a savanna drainage network resulted in landscape units distinguishable by geomorphology, geomorphic boundaries and vegetation pattern. Therefore, the drainage network is a useful template to expose and organize the complexity in savanna landscapes into easily managed and researched units. This perspective should inform a shift from single-scale phytosociological views of homogeneous vegetation units towards multi-scale conceptualizations of savannas as water dependent ecosystems. [source] Twenty years of rest returns grazing potential, but not palatable plant diversity, to Karoo rangeland, South AfricaJOURNAL OF APPLIED ECOLOGY, Issue 4 2010Colleen L. Seymour Summary 1.,Up to 73% of the world's rangelands are degraded, and increasing demand for meat in developing countries and a growing human population are likely to exert even greater pressures on rangelands in the next 20,50 years. Restoration of rangeland grazing potential and resilience is therefore important, particularly in the face of climate change. 2.,We investigated the influence of past stocking rates (from 1910 to 1987), rainfall, and current grazing regimes (from 1988 to 2008) on plant assemblages, grazing potential, and diversity of palatable species in southern Karoo rangelands, South Africa. 3.,We used herbivore exclusion experiments to test whether resting rangeland for 20 years enables recovery of plant assemblages (where seed sources are present within 50 m), regardless of previous grazing history. Mean annual rainfall over this period was 15% higher than the mean annual rainfall for the preceding 80 years and included two exceptionally wet years. 4.,While rainfall was a primary driver of total vegetation cover, grazing history explained differences in plant species composition: plots with shared historical grazing intensity were more similar than plots with the same grazing regimes between 1988 and 2008. 5.,In historically heavily-grazed exclusion plots, cover of the palatable species Tripteris sinuata (formerly Osteospermum sinuatum) returned to levels comparable to that in both exclusion and lightly-grazed plots with a moderate grazing history. Five palatable species (Pteronia empetrifolia, Tetragonia spicata, Berkheya spinosa, Hereroa latipetala and Ruschia spinosa) failed to re-establish, however, despite the presence of seed-producing plants nearby. Furthermore, only cover of P. empetrifolia increased significantly in historically moderately-grazed plots. Cover of unpalatable plants (e.g. Pteronia pallens) increased in all plots over time. 6.Synthesis and applications. These findings suggest that present species composition of arid shrublands reflects historical management at time scales greater than 20 years. Despite high rainfall enabling the return of grazing potential through recovery of a single forage species, rest alone did not ensure the return of all palatable species, with implications for rangeland resilience. Restoring the full suite of palatable species over management timeframes will require more complex interventions such as reseeding or selective clearing. [source] Taxonomic homogenization and differentiation across Southern Ocean Islands differ among insects and vascular plantsJOURNAL OF BIOGEOGRAPHY, Issue 2 2010Justine D. Shaw Abstract Aim, To investigate taxonomic homogenization and/or differentiation of insect and vascular plant assemblages across the Southern Ocean Islands (SOI), and how they differ with changing spatial extent and taxonomic resolution. Location, Twenty-two islands located across the Southern Ocean, further subdivided into five island biogeographical provinces. These islands are used because comprehensive data on both indigenous and non-indigenous insect and plant species are available. Methods, An existing database was updated, using newly published species records, identifying the indigenous and non-indigenous insect and vascular plant species recorded for each island. Homogenization and differentiation were measured using Jaccard's index (JI) of similarity for assemblages across all islands on a pairwise basis, and for island pairs within each of the biogeographical provinces. The effects of taxonomic resolution (species, genus, family) and distance on levels of homogenization or differentiation were examined. To explore further the patterns of similarity among islands for each of the taxa and groupings (indigenous and non-indigenous), islands were clustered based on JI similarity matrices and using group averaging. Results, Across the SOI, insect assemblages have become homogenized (0.7% increase in similarity at species level) while plant assemblages have become differentiated at genus and species levels. Homogenization was recorded only when pairwise distances among islands exceeded 3000 km for insect assemblages, but distances had to exceed 10,000 km for plant assemblages. Widely distributed non-indigenous plant species tend to have wider distributions across the SOI than do their insect counterparts, and this is also true of the indigenous species. Main conclusions, Insect assemblages across the SOI have become homogenized as a consequence of the establishment of non-indigenous species, while plant assemblages have become more differentiated. The likely reason is that indigenous plant assemblages are more similar across the SOI than are insect assemblages, which show greater regionalization. Thus, although a suite of widespread, typically European, weedy, non-indigenous plant species has established on many islands, the outcome has largely been differentiation. Because further introductions of insects and vascular plants are probable as climates warm across the region, the patterns documented here are likely to change through time. [source] Floristic patterns and plant traits of Mediterranean communities in fragmented habitatsJOURNAL OF BIOGEOGRAPHY, Issue 7 2006Guillem Chust Abstract Aim, To contrast floristic spatial patterns and the importance of habitat fragmentation in two plant communities (grassland and scrubland) in the context of ecological succession. We ask whether plant assemblages are affected by habitat fragmentation and, if so, at what spatial scale? Does the relative importance of the niche differentiation and dispersal-limitation mechanisms change throughout secondary succession? Is the dispersal-limitation mechanism related to plant functional traits? Location, A Mediterranean region, the massif of Albera (Spain). Methods, Using a SPOT satellite image to describe the landscape, we tested the effect of habitat fragmentation on species composition, determining the spatial scale of the assemblage response. We then assessed the relative importance of dispersal-related factors (habitat fragmentation and geographical distance) and environmental constraints (climate-related variables) influencing species similarity. We tested the association between dispersal-related factors and plant traits (dispersal mode and life form). Results, In both community types, plant composition was partially affected by the surrounding vegetation. In scrublands, animal-dispersed and woody plants were abundant in landscapes dominated by closed forests, whereas wind-dispersed annual herbs were poorly represented in those landscapes. Scrubby assemblages were more dependent on geographical distance, habitat fragmentation and climate conditions (temperature, rainfall and solar radiation); grasslands were described only by habitat fragmentation and rainfall. Plant traits did not explain variation in spatial structuring of assemblages. Main conclusions, Plant establishment in early Mediterranean communities may be driven primarily by migration from neighbouring established communities, whereas the importance of habitat specialization and community drift increases over time. Plant life forms and dispersal modes did not explain the spatial variation of species distribution, but species richness within the community with differing plant traits was affected by habitat patchiness. [source] Ecosystem engineering across ecosystems: do engineer species sharing common features have generalized or idiosyncratic effects on species diversity?JOURNAL OF BIOGEOGRAPHY, Issue 2 2006Ernesto I. Badano Abstract Aim, To integrate the effects of ecosystem engineers (organisms that create, maintain or destroy habitat for other species) sharing the same archetype on species diversity, and assess whether different engineer species have generalized or idiosyncratic effects across environmentally similar ecosystems. Location, High-Andean habitats of Chile and Argentina, from 23° S to 41° S. Methods, We measured and compared the effects of eight alpine plants with cushion growth-form on species richness, species diversity (measured as the Shannon,Wiener index) and evenness of vascular plant assemblages across four high-Andean ecosystems of Chile and Argentina. Results, The presence of cushion plants always increased the species richness, diversity (measured as the Shannon,Wiener index) and evenness of high-Andean plant assemblages. However, while the presence of different cushion species within the same ecosystem controlled species diversity in the same way, these effects varied between cushion species from different ecosystems. Main conclusions, Results consistently supported the idea that increases in habitat complexity due to the presence of ecosystem engineers, in this case cushion plants, would lead to higher community diversity. Results also indicate that effects of the presence of different cushion species within the same ecosystem could be generalized, while the effects of cushion species from different ecosystems should be considered idiosyncratic. [source] Beyond biomass: measuring the effects of community-level nitrogen enrichment on floral traits, pollinator visitation and plant reproductionJOURNAL OF ECOLOGY, Issue 3 2010Laura A. Burkle Summary 1.,Nitrogen (N) limits primary productivity in many systems and can have dramatic effects on plant,herbivore interactions, but its effects on mutualistic interactions at the community level are not well-understood. The reproduction of many plants depends on both soil N and pollination, and N may affect floral traits, such as flower number or size, which are important for pollinator attraction to plant individuals and communities. 2.,Thus, N may influence plant biomass and reproduction directly as well as indirectly via changes in pollination. The degree to which the effects of N enrichment scale from plant individuals to assemblages through emerging community-level changes in species interactions, like pollination, is relatively unknown. 3.,For 4 years, we tested how N addition to subalpine plant assemblages in Colorado, USA, affected primary productivity and species diversity, floral traits and plant,pollinator interactions, and components of female and male plant reproduction. 4.,At the community level, we found that high-N addition favoured the biomass and seed production of grasses, whereas low-N addition promoted forb growth, flower production and pollinator visitation. However, using a pollen supplementation experiment, we found no evidence that N addition altered patterns of pollen limitation of seed production. Pollinators distributed themselves evenly across floral resources such that per-flower visitation rate did not differ among N treatments. Thus, individual plants did not incur any extra benefit or cost from community-level changes in plant,pollinator interactions that resulted from N enrichment, and the effects of N on forb reproduction were direct. 5.,Synthesis. Understanding how mutualistic and antagonistic species interactions influence individual and community responses to abiotic resources may provide insight to the dominant forces structuring communities and is especially important in the context of predicting the effects of environmental change. In this case, the direct effects of N addition on plants were stronger than the indirect effects mediated through plant,pollinator interactions, thus supporting the concept of bottom-up resource limitation controlling plant response. [source] Effects of patch size and density on flower visitation and seed set of wild plants: a pan-European approachJOURNAL OF ECOLOGY, Issue 1 2010Jens Dauber Summary 1.,Habitat fragmentation can affect pollinator and plant population structure in terms of species composition, abundance, area covered and density of flowering plants. This, in turn, may affect pollinator visitation frequency, pollen deposition, seed set and plant fitness. 2.,A reduction in the quantity of flower visits can be coupled with a reduction in the quality of pollination service and hence the plants' overall reproductive success and long-term survival. Understanding the relationship between plant population size and/or isolation and pollination limitation is of fundamental importance for plant conservation. 3.,We examined flower visitation and seed set of 10 different plant species from five European countries to investigate the general effects of plant populations size and density, both within (patch level) and between populations (population level), on seed set and pollination limitation. 4.,We found evidence that the effects of area and density of flowering plant assemblages were generally more pronounced at the patch level than at the population level. We also found that patch and population level together influenced flower visitation and seed set, and the latter increased with increasing patch area and density, but this effect was only apparent in small populations. 5.,Synthesis. By using an extensive pan-European data set on flower visitation and seed set we have identified a general pattern in the interplay between the attractiveness of flowering plant patches for pollinators and density dependence of flower visitation, and also a strong plant species-specific response to habitat fragmentation effects. This can guide efforts to conserve plant,pollinator interactions, ecosystem functioning and plant fitness in fragmented habitats. [source] Invasive alien plants infiltrate bird-mediated shrub nucleation processes in arid savannaJOURNAL OF ECOLOGY, Issue 4 2007S. J. MILTON Summary 1,The cultivation and dissemination of alien ornamental plants increases their potential to invade. More specifically, species with bird-dispersed seeds can potentially infiltrate natural nucleation processes in savannas. 2To test (i) whether invasion depends on facilitation by host trees, (ii) whether propagule pressure determines invasion probability, and (iii) whether alien host plants are better facilitators of alien fleshy-fruited species than indigenous species, we mapped the distribution of alien fleshy-fruited species planted inside a military base, and compared this with the distribution of alien and native fleshy-fruited species established in the surrounding natural vegetation. 3Abundance and diversity of fleshy-fruited plant species was much greater beneath tree canopies than in open grassland and, although some native fleshy-fruited plants were found both beneath host trees and in the open, alien fleshy-fruited plants were found only beneath trees. 4Abundance of fleshy-fruited alien species in the natural savanna was positively correlated with the number of individuals of those species planted in the grounds of the military base, while the species richness of alien fleshy-fruited taxa decreased with distance from the military base, supporting the notion that propagule pressure is a fundamental driver of invasions. 5There were more fleshy-fruited species beneath native Acacia tortilis than beneath alien Prosopis sp. trees of the equivalent size. Although there were significant differences in native plant assemblages beneath these hosts, the proportion of alien to native fleshy-fruited species did not differ with host. 6Synthesis. Birds facilitate invasion of a semi-arid African savanna by alien fleshy-fruited plants, and this process does not require disturbance. Instead, propagule pressure and a few simple biological observations define the probability that a plant will invade, with alien species planted in gardens being a major source of propagules. Some invading species have the potential to transform this savanna by overtopping native trees, leading to ecosystem-level impacts. Likewise, the invasion of the open savanna by alien host trees (such as Prosopis sp.) may change the diversity, abundance and species composition of the fleshy-fruited understorey. These results illustrate the complex interplay between propagule pressure, facilitation, and a range of other factors in biological invasions. [source] Reconciling plant strategy theories of Grime and TilmanJOURNAL OF ECOLOGY, Issue 6 2005JOSEPH M. CRAINE Summary 1The theories of Grime and Tilman are ambitious attempts to unify disparate theories regarding the construction of plants, their interaction with the environment and the assembly of communities. After over two decades of parallel research, their ideas have not been reconciled, hindering progress in understanding the functioning of ecosystems. 2Grime's theories do not adequately incorporate the importance of non-heterogeneous supplies of nutrients and how these supplies are partitioned over long time scales, are inconsistent regarding the importance of disturbance in nutrient-limited habitats and need to reconsider the carbon economy of shade-tolerant plants. 3Failure to account for differences between aquatic and terrestrial systems in how resource supplies are partitioned led Tilman to develop a shifting set of theories that have become reduced in mechanistic detail over time. The most recent highlighted the reduction of nutrient concentrations in soil solution, although it can no longer be derived from any viable mechanistic model. The slow diffusion of nutrients in soils means that the reduction of average soil solution nutrient concentrations cannot explain competitive exclusion. 4Although neither theory, nor a union of the two, adequately characterizes the dynamics of terrestrial plant assemblages, the complementarity in their assumptions serve as an important foundation for future theory and research. 5Reconciling the approaches of Grime and Tilman leads to six scenarios for competition for nutrients and light, with the outcome of each depending on the ability of plants to pre-empt supplies. Under uniform supplies, pulses or patches, light competition requires leaf area dominance, while nutrient competition requires root length dominance. There are still important basic questions regarding the nature of nutrient supplies that will need to be answered, but recent research brings us closer to a unified set of theories on resource competition. [source] Role of host identity in effects of phytogenic mounds on plant assemblages and species richness on coastal arid dunesJOURNAL OF VEGETATION SCIENCE, Issue 5 2007Magdy I. El-Bana Abstract Question: Phytogenic mounds (nebkhas) - the natural accumulation of wind-blown sediments within or around the canopies of plants - have been proposed as important structures for locally maintaining high species richness in coastal and arid ecosystems. Nebkhas are assumed to increase habitat heterogeneity, but what is the importance of the nebkha host species relative to other nebkha characteristics in determining the associated plant assemblages? Are some host species more effective in creating diversity hotspots, or does a single species-area relationship apply to all nebkhas, regardless of host species? Can the influence of the host be ascribed to its indirect effects on abiotic attributes of the nebkha complex? Methods and location: We investigated plant species richness and composition on nebkhas around six psammophytic species on Mediterranean coastal dunes of the Sinai Peninsula. Results: Plant species richness was significantly related to nebkha size by the single power function according to the general prediction of island biogeography theory, but this relationship was modified - though to a limited degree - by nebkha host species identity. Canonical Correspondence Analysis revealed that nebkha host species identity and nebkha environmental and non-environmental factors significantly explained species composition on the nebkhas, but host species identity did so to a greater extent. The latter might reflect differences in seed trapping ability or free space for colonization between host species. Conclusion: Differences in community composition and richness among nebkhas formed by different host species represent a key factor in the maintenance of plant diversity on arid coastal dunes. [source] Association of ecotones with relative elevation and fire in an upland Florida landscapeJOURNAL OF VEGETATION SCIENCE, Issue 3 2006E.A. Boughton Abstract: Question: What are the importance of elevation and fire in maintaining ecotones of Florida scrub assemblages along a gradual topographic gradient? Location: Archbold Biological Station (ABS), 12 km south of Lake Placid, Florida, USA. Methods: Vegetation cover of upland Florida shrublands was quantified using the line-intercept method along 20 transects traversing similar elevation gradients, stratified by time since fire (TSF). We objectively identified shrubland ecotones using a split moving windows boundary analysis (SMW) with three different window widths. Non-metric multidimensional scaling ordination was used to determine relationships among plant assemblages defined by SMW. Results: We located up to four ecotones per transect, the majority of which were wide, highly heterogeneous zones. Relative elevation controlled the distribution of plant assemblages in upland Florida shrublands. Ecotones in shrublands > 30 years TSF had relatively low dissimilarity values in SMW, indicating that previously discrete plant assemblages with longer TSF were becoming more similar with time. Conclusions Split Moving Windows (SMW) analysis identified ecotones relatively well although patches generated by oak clonal growth were sometimes identified as ecotones. Fire suppression caused ecotones to become more diffuse, suggesting that without fire at least every 30 years, discrete plant assemblages within upland Florida shrublands will be more continuous. [source] Loss of consumers alters the effects of resident assemblages on the local spread of an introduced macroalgaOIKOS, Issue 2 2009F. Bulleri Despite the great interest for the role played by resident assemblages in regulating biological invasions, few studies have assessed how these can influence the spread of exotic species that have successfully established or have included more than one trophic level. On shallow rocky reefs, we assessed how the effects of different benthic assemblages on the spread of an invasive alga, Caulerpa racemosa, are influenced by alterations in the density and species composition of the resident sea urchin assemblage. In order to simulate herbivore species loss scenarios, assemblages dominated by different morphological groups of algae (i.e. turfs or encrusting corallines) or experimentally cleared plots (i.e. bare rock) were exposed to grazing by different combinations of species (Arbacia lixula and Paracentrotus lividus) and densities (natural, ,50% and ,100% of natural densities) of urchins. Algal turfs and encrusting corallines generally facilitated C. racemosa. Manipulating urchins assemblages did not affect the cover and density of fronds of C. racemosa. In contrast, halving the density of P. lividus favoured the penetration of stolons of C. racemosa, consistently among algal assemblages. Other effects of urchins varied among algal assemblages, indicating interactions between trophic levels. In algal turfs, the total removal of urchins caused a decrease in the penetration of stolons, while it enhanced the length of fronds, indicating a shift in the growth form of this clonal plant and, ultimately, a depression of its spreading ability. In bare or encrusting corallines dominated surfaces, the removal of urchins had positive effects on the penetration of stolons and on the length of fronds of C. racemosa, irrespective of one or two species being manipulated and for the intensity of their removal. Our results show that tradeoffs between negative and positive effects of herbivores, varying according to relative densities of species and to the direction and strength of the effects of resident plant assemblages, can influence local rates of spread of C. racemosa. Thus, not only facilitation of exotics by natives can be key in enhancing the spread of exotic species, but it can occur between organisms at different trophic levels. Finally, our findings have important implications for the management of C. racemosa, in view of the progressive domination of shallow rocky reefs by algal turfs. [source] Control of plant species diversity and community invasibility by species immigration: seed richness versus seed densityOIKOS, Issue 1 2003Rebecca L. Brown Immigration rates of species into communities are widely understood to influence community diversity, which in turn is widely expected to influence the susceptibility of ecosystems to species invasion. For a given community, however, immigration processes may impact diversity by means of two separable components: the number of species represented in seed inputs and the density of seed per species. The independent effects of these components on plant species diversity and consequent rates of invasion are poorly understood. We constructed experimental plant communities through repeated seed additions to independently measure the effects of seed richness and seed density on the trajectory of species diversity during the development of annual plant communities. Because we sowed species not found in the immediate study area, we were able to assess the invasibility of the resulting communities by recording the rate of establishment of species from adjacent vegetation. Early in community development when species only weakly interacted, seed richness had a strong effect on community diversity whereas seed density had little effect. After the plants became established, the effect of seed richness on measured diversity strongly depended on seed density, and disappeared at the highest level of seed density. The ability of surrounding vegetation to invade the experimental communities was decreased by seed density but not by seed richness, primarily because the individual effects of a few sown species could explain the observed invasion rates. These results suggest that seed density is just as important as seed richness in the control of species diversity, and perhaps a more important determinant of community invasibility than seed richness in dynamic plant assemblages. [source] Land crabs as key drivers in tropical coastal forest recruitmentBIOLOGICAL REVIEWS, Issue 2 2009Erin Stewart Lindquist ABSTRACT Plant populations are regulated by a diverse assortment of abiotic and biotic factors that influence seed dispersal and viability, and seedling establishment and growth at the microsite. Rarely does one animal guild exert as significant an influence on different plant assemblages as land crabs. We review three tropical coastal ecosystems,mangroves, island maritime forests, and mainland coastal terrestrial forests,where land crabs directly influence forest composition by limiting tree establishment and recruitment. Land crabs differentially prey on seeds, propagules and seedlings along nutrient, chemical and physical environmental gradients. In all of these ecosystems, but especially mangroves, abiotic gradients are well studied, strong and influence plant species distributions. However, we suggest that crab predation has primacy over many of these environmental factors by acting as the first limiting factor of tropical tree recruitment to drive the potential structural and compositional organisation of coastal forests. We show that the influence of crabs varies relative to tidal gradient, shoreline distance, canopy position, time, season, tree species and fruiting periodicity. Crabs also facilitate forest growth and development through such activities as excavation of burrows, creation of soil mounds, aeration of soils, removal of leaf litter into burrows and creation of carbon-rich soil microhabitats. For all three systems, land crabs influence the distribution, density and size-class structure of tree populations. Indeed, crabs are among the major drivers of tree recruitment in tropical coastal forest ecosystems, and their conservation should be included in management plans of these forests. [source] | ||||||||||