Habitat diversity associated to island size and environmental filtering control the species richness of rock‐savanna plants in neotropical inselbergs

Disentangling the multiple factors controlling species diversity is a major challenge in ecology. Island biogeography and environmental filtering are two influential theories emphasizing respectively island size and isolation, and the abiotic environment, as key drivers of species richness. However, few attempts have been made to quantify their relative importance and investigate their mechanistic basis. Here, we applied structural equation modelling, a powerful method allowing test of complex hypotheses involving multiple and indirect effects, on an island‐like system of 22 French Guianan neotropical inselbergs covered with rock‐savanna. We separated the effects of size (rock‐savanna area), isolation (density of surrounding inselbergs), environmental filtering (rainfall, altitude) and dispersal filtering (forest‐matrix openness) on the species richness of all plants and of various ecological groups (terrestrial versus epiphytic, small‐scale versus large‐scale dispersal species). We showed that the species richness of all plants and terrestrial species was mainly explained by the size of rock‐savanna vegetation patches, with increasing richness associated with higher rock‐savanna area, while inselberg isolation and forest‐matrix openness had no measurable effect. This size effect was mediated by an increase in terrestrial‐habitat diversity, even after accounting for increased sampling effort. The richness of epiphytic species was mainly explained by environmental filtering, with a positive effect of rainfall and altitude, but also by a positive size effect mediated by enhanced woody‐plant species richness. Inselberg size and environmental filtering both explained the richness of small‐scale and large‐scale dispersal species, but these ecological groups responded in opposite directions to altitude and rainfall, that is positively for large‐scale and negatively for small‐scale dispersal species. Our study revealed both habitat diversity associated with island size and environmental filtering as major drivers of neotropical inselberg plant diversity and showed the importance of plant species growth form and dispersal ability to explain the relative importance of each driver.     

Landscape-scale connectivity and fragment size determine species composition of grassland fragments

As a consequence of agricultural intensification and habitat fragmentation since the mid-20th century, biological diversity has declined considerably throughout the world, particularly in Europe. We assessed how habitat and landscape-scale heterogeneity, such as variation in fragment size (small vs. large) and landscape configuration (measured as connectivity index), affect plant and arthropod diversity. We focused on arthropods with different feeding behaviour and mobility, spiders (predators, moderate dispersal), true bugs (mainly herbivores and omnivores with moderate dispersal), wild bees (pollinators with good dispersal abilities), and wasps (pollinators, omnivores with good dispersal abilities). We studied 60 dry grassland fragments in the same region (Hungarian Great Plain); 30 fragments were represented by the grassland component of forest-steppe stands, and 30 were situated on burial mounds (kurgans). Forest-steppes are mosaics of dry grasslands with small forests in a matrix of plantation forests. Kurgans are ancient burial mounds with moderately disturbed grasslands surrounded by agricultural fields. The size of fragments ranged between 0.16–6.88 ha (small: 0.16–0.48 ha, large: 0.93–6.88 ha) for forest-steppes and 0.01–0.44 ha (small: 0.01–0.10 ha and large: 0.20–0.44 ha) for kurgans. Fragments also represented an isolation gradient from almost cleared and homogenous landscapes, to landscapes with relatively high compositional heterogeneity. Fragment size, connectivity, and their interaction affected specialist and generalist species abundances of forest-steppes and kurgans. Large fragments had higher species richness of ground-dwelling spiders, and the effect of connectivity was more strongly positive for specialist arthropods and more strongly negative for generalists in large than in small fragments. However, we also found a strong positive impact of connectivity for generalist plants in small kurgans in contrast to larger ones. We conclude that besides the well-known effect of enhancing habitat quality, increasing connectivity between fragments by restoring natural and semi-natural habitat patches would help to maintain grassland biodiversity.     

Non‐interacting impacts of fertilization and habitat area on plant diversity via contrasting assembly mechanisms

Aim

The local‐ and regional‐based forms of anthropogenic change reducing grassland diversity are generally identified, but these scale‐dependent processes tend to co‐occur with unclear interactive effects. Here, we explicitly test how common local and regional perturbations simultaneously affect plant alpha and beta diversity in a multiyear community assembly experiment using fragments of grassland habitat of various sizes. We hypothesized that local disturbances and decreasing patch size would interact, suppressing local diversity while homogenizing composition among patches.

Location

North America.

Methods

We conducted a three‐year grassland assembly experiment, factorially manipulating local perturbation (nitrogen addition and mowing) and patch area for 36 patches over 13 ha. We quantified the individual and interactive effects of these local and regional factors on plant alpha and beta diversity within (quadrat scale) and among patches (patch scale). We also used a null model approach to disentangle between stochastic‐ and niche‐based assembly mechanisms.

Results

We detected a gradient of assembly outcomes driven by two non‐interacting factors—the effects of N fertilization on alpha (negative) and beta (positive) diversity regardless of spatial scale and the scale‐dependant effect of increasing patch size on alpha (positive) and beta (positive) diversity. These effects unfolded over time, with the constraints on richness and composition shifting from dispersal‐based during the first sampling year to perturbation‐and size‐based factors at year two and three. Fertilization effects were driven by a mixture of deterministic (i.e., selection at the species level) and stochastic (i.e., random extinctions) processes resulting in a decline in local richness but an increase in spatial heterogeneity in species composition. Area appeared to influence alpha diversity mainly via stochastic “sampling effect”—larger patches represented a larger sample of the regional pool. Niche‐based processes, however, led to convergence in beta diversity among smaller patches driving a positive overall effect of area on beta diversity.

Main conclusion

Our results illustrate how diversity regulation in contemporary grasslands can be simultaneously shaped by local and regional factors acting additively but via contrasting assembly mechanisms that operate at different spatial and temporal scales.

     

What saplings can tell us about forest expansion over natural grasslands

Questions: 1. Do the species composition, richness and diversity of sapling communities vary significantly in differently sized patches? 2. Do forest patches of different sizes differ in woody plant colonization patterns? Location: São Francisco de Paula, Rio Grande do Sul, Brazil, 29°28'S,50°13'W. Methods: Three woody vegetation types, differing in structural development (patch size) and recovering for 10 years from cattle and burning disturbances, were sampled on grassland. We analysed the composition and complexity of the woody sapling communities, through relative abundance, richness and diversity patterns. We also evaluated recruitment status (residents vs. colonizers) of species in communities occurring in different forest patch size classes. Results : 1. There is a compositional gradient in sapling communities strongly associated with forest patch area. 2. Richness and diversity are positively correlated to patch area, but only in poorly structured patches; large patches present richness and diversity values similar to small patches. 3. Resident to colonizer abundance ratio increases from nurse plants to large patches. The species number proportion between residents and colonizers is similar in small and large patches and did not differ between these patch types. 4. Large patches presented a high number of exclusive species, while nurse plants and small patches did not. Conclusions: Woody plant communities in Araucaria forest patches are associated with patch structure development. Richness and diversity patterns are linked to patch colonization patterns. Generalist species colonize the understorey of nurse plants and small patches; resident species cannot recruit many new individuals. In large patches, sapling recruitment by resident adults precludes the immigration of new species into the patches, limiting richness and diversity.     

Landscape matrix modifies richness of plants and insects in grassland fragments

There is an increasing awareness that not only area and isolation, but also the characteristics of the landscape surrounding habitat patches influence population persistence and species diversity in fragmented landscapes. In this study, we examine the effects of grassland fragmentation and land use in the landscape matrix (on a 2 km scale) on species richness of plants, butterflies, bees and hoverflies. These organisms were studied in replicated remnant patches of different sizes and isolation, embedded in landscapes dominated either by forest, arable land or a mix of these. We found positive effects of patch area on species richness of the three insect taxa, but not of plants. Isolation had a negative effect only on hoverflies. Matrix type had contrasting effects on the studied taxa. Species richness of plants and butterflies was lowest in patches in landscapes dominated by arable land and highest in forest‐dominated landscapes. For hoverflies, the negative effect of small patch area was strongest in forest‐dominated landscapes, and there was a similar non‐significant trend for bees. Our study shows the importance of considering matrix characteristics when studying responses to habitat fragmentation. Differences in matrix response among organism groups probably impinge on differing mechanisms. A forest matrix is likely to provide additional resources for butterflies but either constitute a barrier to dispersal or deprive resources as compared to an arable matrix for hoverflies. Enhanced plant diversity in grassland patches embedded in forested landscapes can be explained by habitat generalists more easily invading these patches, or by an unpaid extinction debt in these landscapes.     

Sunken roads as habitats for forest plant species in a dynamic agricultural landscape: effects of age and isolation

Aim This study tests the hypothesis that linear, woody habitat patches surrounding small, sunken rural roads not only function as an unstable sink but also as a true, sustainable habitat for forest plants. Furthermore, factors affecting the presence of forest plant species in sunken roads are determined. Finally, the implications of these findings for the overall metapopulation dynamics of forest plant species in fragmented agricultural landscapes are assessed. Location The study area, c. 155 km² in size, is situated in a fragmented agricultural landscape within the loamy region of central Belgium. Methods Forest species presence–absence data were collected for 389 sunken roads. The effect of area, depth, age and isolation on sunken road species richness was assessed using linear regression and analysis of variance (anova ). Analysis of covariance was employed to study the interaction between age and isolation. Differences in plant community dispersal spectra in relation to sunken road age and isolation were analysed by means of linear regression and anova . Results Sunken roads proved to function as an important habitat for forest plants. The sink‐hypothesis was falsified by a clear species accumulation in time: sunken road species richness significantly increased with the age of the elements. Sunken road age mainly affected species richness through effects on both area and depth, affecting habitat quality and diversity. Furthermore, sunken road isolation had a significant impact on species richness as well, with the number of forest species decreasing with increasing isolation of the elements, indicating dispersal limitation in sunken road habitats. Moreover, a significant age × isolation interaction effect was demonstrated. Differences in regression slopes for isolation between age classes revealed that the effect of isolation intensified with increasing age of the elements. Differential colonization in relation to forest species dispersal capacities probably account for this, as confirmed by the analysis of sunken road plant community dispersal spectra, with the fraction of species with low dispersal capacities increasing with increasing age and decreasing isolation of the elements. Main conclusions During sunken road development, area and depth increase and, gradually, suitable habitat conditions for forest plant species arise. Depending on their ecological requirements and dispersal capacities, forest species progressively colonize these habitats as a function of the element's isolation. The functioning of sunken roads as a sustainable habitat for forest species enhances the metapopulation viability of forest plants in agricultural landscapes and has important consequences for forest restoration practices. Moreover, the results of this work call for integrating the presence of forest species in small‐scaled linear habitat patches in forest fragmentation studies.     

How landscape modulators function: woody plant impact on seed dispersal and abiotic filtering

The Mediterranean landscape is characterized by a heterogeneous structure: a mosaic of woody plants (trees or shrubs) with scattered patches of herbaceous vegetation. Although the herbaceous and woody patches are adjacent to each other, plant species composition in them is substantially different. This could be attributed to either differences in environmental conditions between patch types (i.e., abiotic filters), or to dispersal limitations caused by the woody plants acting as dispersal filters. In this article, we focus on the relative impact of woody plants, applying these two filter types, in determining plant species composition in Mediterranean woodland. We experimentally manipulated shade and litter cover and examined the effect of each of these factors on plant species composition. We used seed-traps to evaluate seed arrival in the patches, and experimentally removed the shrub canopy to study the effect of the shrub as a physical barrier to seed entry. Results showed that plant species number and composition were not significantly affected by shade and litter manipulation. The number of trapped seeds were significantly higher in the open patches than in the woody patches, and removal of woody plants increased the number of trapped seeds in both open and woody patches, as a result of eliminating the physical obstacle to free seed movement. Our findings show that woody plants affect the herbaceous plant community by influencing seed dispersal, and highlight that they affect other organisms not only by modifying resource availability but also through the creation of a new landscape structure.     

Recent Changes in Patch Characteristics and Plant Communities in the Jalca Grasslands of the Peruvian Andes

Habitat loss and fragmentation are considered major threats to biodiversity, especially in tropical mountain ecosystems. Most studies focus on the relationships between biodiversity and patch characteristics such as patch size, connectivity or degree of contrast with the surrounding matrix, but leave the rate of change within these variables little explored. We analyzed the importance of changes in patch characteristics over time on species diversity and species composition in the paramo of northern Peru, a tropical grassland ecosystem, locally known as jalca. We obtained land use/cover maps for 1987 and 2007 spanning an area of 6300 km², and quantified land use change, jalca patch characteristics and their proportional changes over 20 yr. In 2009, 371 vascular plant species were recorded in 92 plots, each plot representative of single patches. Between 1987 and 2007, jalca cover decreased from 47 to 35 percent due to encroaching agriculture. This activity showed an upward shift probably favored by climate change. The number of jalca patches increased, mean patch size decreased, and the patches showed a higher contrast with the surrounding matrix. Multiple linear regression failed to show that species diversity relates to changes in patch characteristics. Canonical correspondence analysis indicated that species composition relates to the degree of contrast between the patch and its surrounding matrix and its changes through time. We concluded that changes in patch characteristics are important only for species composition. This study highlights the importance of considering matrix management with a long term perspective for conservation efforts.     

Shrub encroachment alters composition and diversity of ant communities in abandoned grasslands of western Carpathians

Invasions of woody species into grasslands abandoned by agriculture are a global phenomenon, but their effects on diversity of other taxa have been rarely investigated across both regional and local scales. We quantified how shrub encroachment affected the activity, composition, and diversity of ant communities in managed and abandoned grasslands in western Carpathians of Central Europe across four regions and four shrub encroachment stages in each region. We surveyed ant communities on 48 sites in total, with each encroachment stage replicated three times in each region and twelve times overall. We used pitfall traps to sample ants over three years (2008, 2009, 2011) and identified 9,254 ant workers belonging to 33 species in total. Although the epigaeic activity and composition of ant communities varied with region, abandoned grasslands supported a greater species richness of ants than managed grasslands regardless of the region, and especially so in more advanced shrub encroachment stages. Since the woody colonization within grasslands was moderate even in the advanced encroachment stages (on average ~40 % of grassland colonized by woody species), it allowed coexistence of forest specialists (e.g. Temnothorax crassispinus) with species typical of open grasslands, thus increasing overall ant diversity. Managed grasslands were not only less species rich compared to abandoned grasslands, but they were characterized by different species (e.g. Lasius niger, Myrmica rugulosa). The differences in ant communities between managed and abandoned grasslands are likely to cause differences in ecological functions mediated by ants (e.g. predation of arthropods or plant seed dispersal).     

Patch identity and the spatial heterogeneity of woody encroachment in exotic-dominated old-field grasslands

Most grassland communities in agricultural landscapes comprise a mix of exotic and native plants, where grasses and forbs are disposed in low diversity patches conforming a heterogeneous matrix of vegetation. Within these “novel” ecosystems, woody encroachment is one of the principal causes of ecosystem degradation. Here, we examined the resistance to exotic woody establishment (Gleditsia triacanthos) into four different monospecific patches characteristics of old-field grasslands in Inland Pampa: an annual forb (Conium maculatum), an annual grass (Lolium multiflorum), and two perennial grasses (Cynodon dactylon and Festuca arundinacea). We evaluated the filter to tree recruitment by rodent seed removal and survival and growth of Gleditsia seedlings transplanted into undisturbed and disturbed microsites, within each patch. Beneath intact vegetation seed removal was an important biotic filter to woody establishment whereas disturbances facilitated seed survival in patches of perennial grasses. Patch identity affected tree growth, and Cynodon reduced the final biomass compared to forbs. Disturbance enhanced tree performance independently of patch type. After 2 years, tree survival was independent of disturbance and patch identity. As patch identity may regulate granivory and growth of tree saplings, community susceptibility or resistance to woody invasion rather than representing a static community attribute could vary according to the dynamic changes in the proportion of susceptible-resistant patches. Broadly, our work reinforces the concept that mechanisms regulating vegetation heterogeneity add a component of stochasticity to biotic resistance to community plant invasion.     

Plant dispersal strategies and the colonization of Araucaria forest patches in a grassland‐forest mosaic

Questions: In a natural grassland‐forest mosaic: What is the influence of phylogeny and diaspore traits related to disperser attraction (DAT) on (1) seed size/number trade‐off (SSNT) in woody species colonizing forest patches; (2) on the frequency of the species? 3. What is the influence of forest patch area on mean seed size and number. 4. Do phylogeny and DAT expressed at the species level affect this relationship? Location: Campos grassland and Araucaria forest in São Francisco de Paula, RS, Brazil, at ca. 29°28’ S; 50° 13’ W. Methods: Forest patches of different sizes in a grassland site recovering for ten years since human disturbances were surveyed by the relative abundance of vertebrate‐dispersed woody saplings. We described colonizer species according to taxonomic phylogenetic relationships and diaspore type, size and color. We analyzed with a variation partitioning method their influence on SSNT and on species frequency in the patches. At the community level we regressed mean seed size and number on forest patch area and evaluated how these relationships were affected by phylogeny and DAT at the species level. Results: 1. Phylogeny and DAT mostly explained seed size and seed number per diaspore variation. 2. By controlling phylogeny and DAT influence the frequency of species in forest patches was positively associated with their seed number in the diaspores, and negatively associated with their seed size. 3. Mean seed size and seed number at the community level were positively associated with patch area. 4. When phylogeny and DAT influences on seed size were removed this relationship was stronger for seed size and weaker for seed number. Conclusions: 1. Energy allocation to dispersal in detriment of offspring survival increased the successful establishment of colonizer species in forest patches, despite phylogenetic relationships and DAT variation in their diaspores. 2. Although patch area exerted a selective pressure on seed size, habitat preferences of dispersers may also influence patch colonization.     

Role of nurse plants in Araucaria Forest expansion over grassland in south Brazil

Abstract Araucaria Forest expansion over grassland takes place under wet climate conditions and low disturbance and it is hypothesized that isolated trees established on grassland facilitate the establishment of forest woody species beneath their canopies. Forest with Araucaria angustifolia is a particular type of Brazilian Atlantic Forest and the main forest type on the highland plateau in south Brazil, often forming mosaics with natural Campos grassland. The objectives of this paper were to evaluate the role of isolated shrubs and trees as colonization sites for seedlings of Araucaria Forest woody species on grassland, to determine which species function as preferential nurse plants in the process and the importance of vertebrate diaspore dispersal on the structure of seedling communities beneath nurse plants. The study was conducted in São Francisco de Paula, Rio Grande do Sul State, where we sampled isolated shrubs and trees in natural grassland near Araucaria Forest edges. Seedlings were counted and identified, and seedling diaspore dispersal syndromes, size and colour were registered. We detected 11 woody species with a potential role in nucleating grassland colonization by forest species. Beneath the canopies of nurse plants more forest species seedlings were found compared with open field grassland and the seedlings had diaspores mostly dispersed by vertebrates. Also, more seedlings were found under the canopy of A. angustifolia than beneath other nurse plant species. We conclude that A. angustifolia trees established on grassland act as nurse plants, by attracting disperser birds that promote colonization of the site by other forest species seedlings, and that under low level of grassland disturbance, conservation of frugivorous vertebrate assemblages may increase forest expansion over natural grassland and also facilitate the regeneration of degraded forest areas.     

Conserving a variety of ancient forest patches maintains historic arthropod diversity

Forests are naturally extensive tracts. However, in South Africa natural fires over many millennia have reduced forested areas into small remnants spread throughout a grassland matrix. Small patches, especially distant patches, are generally considered to be adverse for forest specialists, owing to decreased forest interior and increased edge. Here we test this assumption by determining the impact of forest interpatch distance and patch size on epigaeic arthropod diversity in this globally rare vegetation type. Forty patches were selected: ten large (100–435 m diameter) that are distant (500–645 m) from other patches, ten large that are close to other patches (38–97 m), ten small (30–42 m) that are distant, and ten small-close patches. Each patch had two plots: edge and interior. Arthropods were sampled using pitfall traps, Berlese-Tullgren funnels and active searches. Interiors and edges had similar species richness and composition, excluding spiders, which were richer in interiors. Patch size significantly influenced species richness of predatory beetles and arthropod assemblages, excluding spiders. Effect of the interaction between patch size and interpatch distance on species richness and composition varied among taxa. Furthermore, large patches supported similar assemblages regardless of interpatch distance. Arthropod response, particularly ants to patch size and interpatch distance, was partly shaped by the matrix type. The percentage of surrounding grassland had little effect on arthropod diversity. We can conclude that large and close patches are important for arthropod conservation. Nevertheless, it is also important to conserve a variety of patch sizes at various distances to maximize overall arthropod composition.     

Nucleation-driven regeneration promotes post-fire recovery in a Chilean temperate forest

Nucleation is a successional process in which extant vegetation facilitates seed dispersal and recruitment of other individuals and species around focal points in the landscape, leading to ecosystem recovery. This is an important process in disturbed sites where regeneration is limited by abiotic conditions or restrictive seed dispersal. We investigated forest recovery in a large burned area of evergreen temperate rainforest in southern Chile subjected to seasonal soil waterlogging, and assessed the relevance of nucleation processes in overcoming biotic and physical barriers for tree species regeneration. We measured richness and abundance of woody species in relation to patch size, as well as abiotic factors such as light and soil moisture within and outside patches. We found higher tree regeneration in existing patches than in open areas. We recorded an increase of patch size over time, associated with the increase in number of individuals and tree species. Soils in open areas were waterlogged, especially in winter, while patches were not. Trees in patches also acted as perches, enhancing bird-mediated seed rain. Seeds of fleshy-fruited tree species arrived first at patches and seedlings were more frequent in smaller, younger patches, while the number of seedlings of trees with wind-dispersed seeds increased in larger, older patches. Our study shows that woody species seem incapable of recruiting in open and waterlogged soils and depend strongly on extant vegetation patches to establish. In this fire-disturbed evergreen temperate forest regeneration occurs via nucleation, where new individuals contribute to a centrifugal kind of patch growth.     

Relationships between spatial configuration of tropical forest patches and woody plant diversity in northeastern Puerto Rico

The destruction and fragmentation of tropical forests are major sources of global biodiversity loss. A better understanding of anthropogenically altered landscapes and their relationships with species diversity and composition is needed in order to protect biodiversity in these environments. The spatial patterns of a landscape may control the ecological processes that shape species diversity and composition. However, there is little information about how plant diversity varies with the spatial configuration of forest patches especially in fragmented tropical habitats. The northeastern part of Puerto Rico provides the opportunity to study the relationships between species richness and composition of woody plants (shrubs and trees) and spatial variables [i.e., patch area and shape, patch isolation, connectivity, and distance to the Luquillo Experimental Forest (LEF)] in tropical forest patches that have regenerated from pasturelands. The spatial data were obtained from aerial color photographs from year 2000. Each photo interpretation was digitized into a GIS package, and 12 forest patches (24–34 years old) were selected within a study area of 28 km². The woody plant species composition of the patches was determined by a systematic floristic survey. The species diversity (Shannon index) and species richness of woody plants correlated positively with the area and the shape of the forest patch. Larger patches, and patches with more habitat edge or convolution, provided conditions for a higher diversity of woody plants. Moreover, the distance of the forest patches to the LEF, which is a source of propagules, correlated negatively with species richness. Plant species composition was also related to patch size and shape and distance to the LEF. These results indicate that there is a link between landscape structure and species diversity and composition and that patches that have similar area, shape, and distance to the LEF provide similar conditions for the existence of a particular plant community. In addition, forest patches that were closer together had more similarity in woody plant species composition than patches that were farther apart, suggesting that seed dispersal for some species is limited at the scale of 10 km.     

The effect of altitude,patch size and disturbance on species richness and density of lianas in montane forest patches

The species richness and density of lianas (woody vines) in tropical forests is determined by various abiotic and biotic factors. Factors such as altitude, forest patch size and the degree of forest disturbance are known to exert strong influences on liana species richness and density. We investigated how liana species richness and density were concurrently influenced by altitude (1700–2360 m), forest patch size, forest patch location (edge or interior) and disturbance intensity in the tropical montane evergreen forests, of the Nilgiri and Palni hills, Western Ghats, southern India. All woody lianas (≥1 cm dbh) were enumerated in plots of 30 × 30 m in small, medium and large forest patches, which were located along an altitudinal gradient ranging from 1700 to 2360 m. A total of 1980 individual lianas were recorded, belonging to 45 species, 32 genera and 21 families, from a total sampling area of 13.86 ha (across 154 plots). Liana species richness and density decreased significantly with increasing altitude and increased with increasing forest patch size. Within forest patches, the proportion of forest edge or interior habitat influenced liana distribution and succession especially when compared across the patch size categories. Liana species richness and density also varied along the altitudinal gradient when examined using eco-physiological guilds (i.e. shade tolerance, dispersal mode and climbing mechanism). The species richness and density of lianas within these ecological guilds responded negatively to increasing altitude and positively to increasing patch size and additionally displayed differing sensitivities to forest disturbance. Importantly, the degree of forest disturbance significantly altered the relationship between liana species richness and density to increasing altitude and patches size, and as such is likely the primary influence on liana response to montane forest succession. Our findings suggest that managing forest disturbance in the examined montane forests would assist in conserving local liana diversity across the examined altitudinal range.     

The effects of plant traits on species' responses to present and historical patch configurations and patch age

Patch configuration is viewed as an important factor affecting the distributions of plant species. Although a number of studies have explored the relationship between plant life‐history traits and species’ distributions in fragmented landscapes, the effect of individual traits on the dependence of species on historical versus current landscape configurations remains unclear. We identified the extent to which present (2000s) and historical (1843, 1954, 1980s) patch configurations (area and connectivity) and patch age affected the distributions of 99 species inhabiting dry calcareous grasslands. We used traits related to dispersal, survival, growth and habitat preferences to explain the dependence of 60 of these species on present and historical configurations, and the age of grassland patches. We found that most of the species had an affinity to currently or historically large, older and more isolated patches. This suggests that many dry grassland species are not in equilibrium with the current landscape, as their distributions still reflect past landscape structures. Rapidly growing species with higher seed bank longevity and nutrient requirements primarily occur in young, large grassland patches whereas species with the opposite traits occur in older, historically large and currently more isolated smaller patches. We hypothesise that patch quality is the reason why different species occupy patches of different age. Species occupying young, large patches commonly disperse by endozoochory. By contrast, no dispersal trait is associated with species occupying old, usually isolated patches. Our results suggest that species occupying old patches are exposed to higher potential risk of extinction, as their distributions are probably limited by the low number and connectivity of available suitable patches and poor dispersal ability. We thus suggest that the dynamics of these species can effectively be supported by improving the quality of young grassland patches.     

Grassland connectivity explains entomophilous plant species assemblages in an agricultural landscape of the Pampa Region,Argentina

The Pampa grassland of Argentina is one of the most highly threatened biomes in the world. A high proportion of the original grassland cover has been transformed into land for agriculture or degraded. In the southern part of the region, fragmented semi‐natural grasslands over exposed rock still persist and connectivity between them is assumed to be crucial for maintaining viable populations. We quantified overall connectivity of grassland patches in a sector of the Southern Pampa region, and investigated the degree to which landscape connectivity explains entomophilous plant species assemblages in a subset of patches. We characterized each of the 301 patches in the landscape by their degree of intra‐patch and inter‐patch connectivity based on graph theory, and considering threshold dispersal distances from 100 to 1000 m. We surveyed entomophilous plant species in 39 grassland patches and classified the species in three categories (annual herbs, perennial herbs and shrubs) considering their different growth form and longevity. The influence of connectivity variables on entomophilous plant species assemblages variation was explored using Canonical Correspondence Analysis. Although grassland patches were poorly connected at all threshold distances, some of them were found to be critical for global connectivity. Connectivity significantly explained total, annual‐biennial and shrub assemblages for all threshold dispersal distances (6–13% of total variation). Variation in annual species assemblages was associated with intra‐patch and inter‐patch connectivity at short distance (100 m), while variation in shrub species assemblages was explained by intra‐patch and inter‐patch connectivity for distances between 100 m and 1000 m. This study evidenced the low connectivity of the study system, allowed the identification of critical areas for conservation, and provided valuable information to develop management strategies in increasingly human‐dominated landscapes.     

Metacommunity size influences aquatic community composition in a natural mesocosm landscape

Ecosystems are often arranged in naturally patchy landscapes with habitat patches linked by dispersal of species in a metacommunity. The size of a metacommunity, or number of patches, is predicted to influence community dynamics and therefore the structure and function of local communities. However, such predictions have yet to be experimentally tested using full food webs in natural metacommunities. We used the natural mesocosm system of aquatic macroinvertebrates in bromeliad phytotelmata to test the effect of the number of patches in a metacommunity on species richness, abundance, and community composition. We created metacommunities of varying size using fine mesh cages to enclose a gradient from a single bromeliad up to the full forest. We found that species richness, abundance, and biomass increased from enclosed metacommunities to the full forest size and that diversity and evenness also increased in larger enclosures. Community composition was affected by metacommunity size across the full gradient, with a more even detritivore community in larger metacommunities, and taxonomic groups such as mosquitoes going locally extinct in smaller metacommunities. We were able to divide the effects of metacommunity size into aquatic and terrestrial habitat components and found that the importance of each varied by species; those with simple life cycles were only affected by local aquatic habitat whereas insects with complex life cycles were also affected by the amount of terrestrial matrix. This differential survival of obligate and non‐obligate dispersers allowed us to partition the beta‐diversity between metacommunities among functional groups. Our study is one of the first tests of metacommunity size in a natural metacommunity landscape and shows that both diversity and community composition are significantly affected by metacommunity size. Synthesis Natural food webs are sensitive to meta‐community size, i.e. the number of patches connected through dispersal. We provide an empirical test using the aquatic foodweb associated within bromeliads as a model system. When we reduced the number of bromeliad patches connect through dispersal, we found a clear change of the foodweb in terms of population sizes, beta diversity, community composition and predator‐prey ratios. The response of individual taxa was predictable based on species traits including dispersal modes, life cycle, and adult resource requirements. Our study demonstrates that community structure is strongly influenced by the interplay of species traits and landscape properties.     

Avian life-history determinants of local extinction risk in a hyper-fragmented neotropical forest landscape

The fact that species vary in their vulnerability to extinction is well documented, but the reasons for these differences remain poorly understood. Why should some species/families/guilds decline rapidly with increasing anthropogenic disturbance, while others either tolerate or proliferate in disturbed habitats? We investigated the bird species composition in 31 primary forest patches of varying size in a region of the Amazonian 'Arc of Deforestation' and assessed which species life-history traits predisposed individual species to extinction. Medium-sized non-flocking canopy frugivores/ominvores of low primary forest dependence were least likely to go extinct in small patches, while small-bodied flock-following primary-forest-dependent terrestrial insectivores were most fragmentation sensitive. We found highly idiosyncratic relationships between the minimum size of forest patches occupied by different species and their territory size requirements estimated based on other Amazonian studies. This suggests that avian assemblages in forest fragments primarily comprise species that either have good dispersal abilities or are highly tolerant to the non-forest matrix, rather than those whose minimum spatial requirements can be met by the size of available forest fragments.