Habitat Patch Size Research Articles

The effect of habitat fragmentation on Malay tapir abundances in Thailand’s protected areas

Habitat loss and fragmentation in tropical regions are major threats to the persistence of endangered Malay tapir (Tapirus indicus). The Malay tapir distribution is largely constrained to fragmented habitats inside protected areas. However, it is unclear how the spatial patterns of habitat fragmentation affect its relative abundance. Here, we investigated the effects of habitat fragmentation on Malay tapir relative abundance in Thailand. We first quantified the spatial patterns of habitat fragmentation within nine of Thailand’s protected areas. Second, we assessed the relationship of fragmentation metrics and relative abundance of Malay tapirs. Third, we identified the relative importance of the fragmentation metrics in explaining relative abundance. We found that tapir abundance remained unexpectedly high in the Southern forest complex despite the fact that tapir habitats were significantly more fragmented there than in the protected area in the western forest complex (p < 0.05). Additionally, we found a significantly negative relation with clumpiness index (R2 = 0.51, p < 0.05). This suggests that other factors may also be influencing their populations, so that the Southern protected areas provide preferred habitat with higher relative proportions of moist evergreen forest, large habitat patch size, precipitation, and elevation. It highlights the importance of interconnected habitat for tapirs, and the benefit of conservation efforts in small, less recognized protected areas.

Overcoming confusion and stigma in habitat fragmentation research.

Anthropogenic habitat loss is widely recognized as a primary environmental concern. By contrast, debates on the effects of habitat fragmentation persist. To facilitate overcoming these debates, here we: (i) review the state of the literature on habitat fragmentation, finding widespread confusion and stigma; (ii) identify consequences of this for biodiversity conservation and ecosystem management; and (iii) suggest ways in which research can move forward to resolve these problems. Confusion is evident from the 25 most-cited fragmentation articles published between 2017 and 2021. These articles use five distinct concepts of habitat fragmentation, only one of which clearly distinguishes habitat fragmentation from habitat area and other factors ('fragmentation per se'). Stigmatization is evident from our new findings that fragmentation papers are more charged with negative sentiments when compared to papers from other subfields in the environmental sciences, and that fragmentation papers with more negative sentiments are cited more. While most empirical studies of habitat fragmentation per se find neutral or positive effects on species and biodiversity outcomes, which implies that small habitat patches have a high cumulative value, confusion and stigma in reporting and discussing such results have led to suboptimal habitat protection policy. For example, government agencies, conservation organizations, and land trusts impose minimum habitat patch sizes on habitat protection. Given the high cumulative value of small patches, such policies mean that many opportunities for conservation are being missed. Our review highlights the importance of reducing confusion and stigma in habitat fragmentation research. To this end, we propose implementing study designs in which multiple sample landscapes are selected across independent gradients of habitat amount and fragmentation, measured as patch density. We show that such designs are possible for forest habitat across Earth's biomes. As such study designs are adopted, and as language becomes more precise, we expect that confusion and stigma in habitat fragmentation research will dissipate. We also expect important breakthroughs in understanding the situations where effects of habitat fragmentation per se are neutral, positive, or negative, and the reasons for these differences. Ultimately this will improve efficacy of area-based conservation policies, to the benefit of biodiversity and people.

Conserving diversity, distinctiveness and connectivity in the Sunshine Coast heathlands, Queensland, Australia

AbstractAustralia is committed to global area‐based conservation targets whilst ensuring its National Reserve system is representative of ecosystem types. However, concern remains for the increasing habitat loss and fragmentation, and the possible impacts of loss of connectivity between remnant vegetation. This study uses a range of diversity metrics to examine the biodiversity conservation status of the Sunshine Coast heathlands, in the South Eastern Queensland bioregion. The pre‐clearing and remnant extent, and the protection status of the nine heath Regional Ecosystems were calculated. Fragmentation and connectivity were examined by comparing heath patch sizes, and by calculating the distance between patches, from pre‐clearing estimates, until 2019. Diversity metrics for the Regional Ecosystems, including phylogenetic metrics, were tested for correlation with habitat extent, patch size, patch number and distance between patches. Of the pre‐clearing extent, 62% of Sunshine Coast heathlands remain and 46% is protected in National Parks. Levels of protection in National Parks vary across the Local Government Areas, and between Regional Ecosystems, and the priority Regional Ecosystems for further protection were identified. There has been habitat loss resulting in reduced patch sizes, and fragmentation due to urbanization, but the number of patches of heath remains intact, and connectivity in terms of distance between patches remains stable. Phylogenetic dispersion, but not diversity, was correlated with the extent of heath and the number of patches. This highlights the opportunity to maintain biodiversity in these heathlands, with the value of small patches of heath identified as key to maintaining connectivity in the coastal lowlands, distinctiveness in the montane heaths and dunes, and overall phylogenetic dispersion. This study has shown how a variety of diversity metrics and landscape analyses can inform on priority areas for biodiversity conservation in the heathlands of an increasingly urbanized region.

The landscape scale of effect on the alpha and beta diversities of woody species in a semideciduous tropical forest

ContextMost tropical forest landscapes are highly fragmented, have habitat patches varying in size and shape, and display different degrees of perturbation, but with high conservation values. Therefore, a major goal of landscape ecology is to discover the actual spatial scale at which landscape composition and structure affect biological processes and biodiversity.ObjectiveThis study aimed to determine the landscape scale of effect governing the α and β diversities of woody species in a highly fragmented, semideciduous tropical forest.MethodsWe recorded the diversity of woody species in 19 plots scattered across a highly fragmented, semideciduous tropical forest landscape. Then, we used CART algorithms to evaluate the effects of landscape attributes on the α and β diversities of such species across 100 scales (10–1000 m) and tested continuous effects with generalized additive models.ResultsThe shape and size of habitat patches in the range of 250–470 m determined α diversity. As for β diversity, nestedness was affected by the shape of forest patches at 510 m, whereas landscape heterogeneity affected species turnover within 100 m buffers.ConclusionWhile a previous study in a similar habitat reported effects at 800 m, the number, size, and shape of habitat patches in the current study accounted for the diversity of the focal plots within 100–510 m. Furthermore, CART effectively screened 100 scales, revealing which landscape attributes correlated the most with the diversity of woody plants. The findings provide valuable guidelines for conservation, restoration efforts, and public policies.

Mean landscape‐scale incidence of species in discrete habitats is patch size dependent

AbstractAimA pervasive negative relationship between the species richness of an assemblage and the mean global range size of the species it contains has recently been identified. Here, we test for an effect of habitat patch size on the mean landscape‐scale incidence (estimating local range size) of constituent species independent of variation in richness.LocationGlobal.Time PeriodContemporary.Major Taxa StudiedVarious.MethodsWe devised a new standardized patch‐scale metric, Mean Species Landscape‐scale Incidences per Patch (MSLIP). Positive values indicate a patch contains more widespread (high‐incidence) species than expected relative to their frequency in the landscape; negative values indicate the presence of more narrow‐range (low‐incidence) species. For 202 metacommunity datasets (archipelagos, habitat islands and fragments) we regressed MSLIP on patch size, testing four hypotheses: (i) no effect (zero slope), (ii) more widespread species in smaller patches (negative slope), (iii) more narrow‐range species in smaller patches (positive slope), (iv) a composite effect (curvilinear/unimodal).ResultsThere was a generally negative curvilinear relationship between MSLIP and patch size, consistent with smaller and larger patches respectively containing more high‐ and low‐incidence species than expected. At intermediate patch sizes, mean species incidence approximates that of the overall landscape. Relative richness mediated this relationship; species‐rich sites of any size increasingly favoured low‐incidence species, species‐poor sites high‐incidence species. Results were consistent for taxonomic groups, and metacommunity types, except aquatic habitat islands.Main ConclusionsThe dependence of mean species incidence on both patch size and relative richness has implications for biodiversity and community assembly theory, or when seeking to understand ecological processes sensitive to species composition (e.g., ecosystem functioning, trophic web structures). We propose the ‘patch size where the MSLIP regression intersects zero’ as a benchmark distinguishing smaller from larger patches, with the expectation small patches preferentially support more high‐incidence and large patches more low‐incidence species.

Social information modifies the associations between forest fragmentation and the abundance of a passerine bird

Habitat loss and fragmentation are the main factors driving the occurrence and abundance of species in the landscape. However, the local occurrence and abundance of species may also depend on conspecific and heterospecific social information e.g. clues of animals’ presence or their voices. We investigated the impact of the interaction between different types of social information and forest fragmentation on the abundance of the song thrush, Turdus philomelos, in Central Europe. Three types of social information (attractive, repulsive, and mixed) and procedural control were broadcasted via loudspeakers in 150 forest patches that varied in size and isolation metrics. Repulsive social information (cues of presence of predator) decreased abundance of song thrush. Also, the repulsive social information changed the association between forest patch isolation, size and the abundance. Attractive social information (songs of the studied thrush) had no effect on song thrush abundance. However, the attractive social information reversed the positive correlation between habitat patch size and the abundance. Mixed social information (both repulsive and attractive) had no impact on the abundance nor interacted with habitat fragmentation. The observed effects mostly did not last to the next breeding season. Overall, our findings indicate that lands of fear and social attraction could modify the effect of habitat fragmentation on the species abundance but these effects probably are not long-lasting.

Predicting the spatial expansion of an animal population with presence-only data.

Predictive models can improve the efficiency of wildlife management by guiding actions at the local, landscape and regional scales. In recent decades, a vast range of modelling techniques have been developed to predict species distributions and patterns of population spread. However, data limitations often constrain the precision and biological realism of models, which make them less useful for supporting decision-making. Complex models can also be challenging to evaluate, and the results are often difficult to interpret for wildlife management practitioners. There is therefore a need to develop techniques that are appropriately robust, but also accessible to a range of end users. We developed a hybrid species distribution model that utilises commonly available presence-only distribution data and minimal demographic information to predict the spread of roe deer (Capreolus caprelous) in Great Britain. We take a novel approach to representing the environment in the model by constraining the size of habitat patches to the home-range area of an individual. Population dynamics are then simplified to a set of generic rules describing patch occupancy. The model is constructed and evaluated using data from a populated region (England and Scotland) and applied to predict regional-scale patterns of spread in a novel region (Wales). It is used to forecast the relative timing of colonisation events and identify important areas for targeted surveillance and management. The study demonstrates the utility of presence-only data for predicting the spread of animal species and describes a method of reducing model complexity while retaining important environmental detail and biological realism. Our modelling approach provides a much-needed opportunity for users without specialist expertise in computer coding to leverage limited data and make robust, easily interpretable predictions of spread to inform proactive population management.

Steady-state dynamics in a two-patch population model with and without Allee effect

Most biological populations reside in landscapes that consist of many different patches of different quality. Different species differ in their movement behavior, habitat preference and growth rates. Historically, mathematical models for population dynamics have made many simplifying assumptions, such as a single patch or homogeneous landscapes. Recent models have begun to implement landscape heterogeneity and individual movement characteristics, but many of those are based on logistic growth and linear analysis of the zero state. We consider a two-patch model with more general growth functions that can include Allee effects. We prove the existence of steady states and classify their qualitative behavior. In some special cases, we explicitly calculate their stability and use these results to give conditions for when the system exhibits bistability, i.e., the coexistence of locally stable states. We also study bifurcations with respect to the size of habitat patches and give conditions for forward and backward bifurcations.

Landscape experiments unlock relationships among habitat loss, fragmentation, and patch-size effects.

Habitat loss is often considered the greatest near-term threat to biodiversity, while the impact of habitat fragmentation remains intensely debated. A key issue of this debate centers on the problem of scale-landscape or patch-at which to assess the consequences of fragmentation. Yet patterns are often confounded across scales, and experimental designs that could solve this scaling problem remain scarce. We conducted two field experiments in 30 experimental landscapes in which we manipulated habitat loss, fragmentation, and patch size for a community of four insect herbivores that specialize on the cactus Opuntia. In the first experiment, we destroyed 2088 Opuntia patches in either aggregated or random patterns and compared the relative effects of landscape-scale loss and fragmentation to those of local patch size on species occurrence. This experiment focused on manipulating the relative separation of remaining patches, where we hypothesized that aggregated loss would disrupt dispersal more than random loss, leading to lower occurrence. In the second experiment, we destroyed 759 Opuntia patches to generate landscapes that varied in patch number and size for a given amount of habitat loss and assessed species occurrence. This experiment focused on manipulating the subdivision of remaining habitat, where we hypothesized that an increase in the number of patches for a given amount of loss would lead to negative effects on occurrence. For both, we expected that occurrence would increase with patch size. We find strong evidence for landscape-scale effects of habitat fragmentation, with aggregated loss and a larger number of patches for a given amount of habitat loss leading to a lower frequency of patches occupied in landscapes. In both experiments, occurrence increased with patch size, yet interactions of patch size and landscape-scale loss and fragmentation drove species occurrence in patches. Importantly, the direction of effects were consistent across scales and effects of patch size were sufficient to predict the effects of habitat loss and fragmentation across entire landscapes. Our experimental results suggest that changes at both the patch and landscape scales can impact populations, but that a long-standing pattern-the patch-size effect-captures much of the key variation shaping patterns of species occurrence.

Spatial scales in instream flow modeling: Why and how to use ecologically appropriate resolutions

AbstractThis paper discusses why and how to use ecologically appropriate spatial resolutions (e.g., cell size or range of cell sizes) when modeling instream flow effects on aquatic animals. Resolution is important because relations between habitat and animal habitat use vary with spatial resolution, and different habitat variables may best predict habitat use at different resolutions. Using appropriate resolutions consistently would bring clarity and coherence to how we quantify and model habitat characteristics and habitat use by fish, facilitate the use of standard and more credible measures of habitat preference, incorporate more fisheries knowledge to improve models for different kinds of fish, and avoid well‐known (and perhaps unknown) biases. Doing so involves describing habitat, and habitat use by fish, with spatially explicit measures with clear resolutions; using the same resolution for physical habitat and fish habitat use; selecting that resolution for ecological reasons; and using habitat variables and fish observation methods appropriate for the resolution. The choice of resolution considers factors such as how much space fish use for specific activities and the size of important habitat patches. For drift‐feeders, cell sizes and fish habitat use observations should use a resolution no smaller than feeding territories. Piscivores typically hunt over large areas so should be modeled with larger habitat units. Models of small and less‐mobile organisms (e.g., benthic invertivores) may need fine resolutions to capture the small areas of unusual habitat they depend on. Because of such differences, instream flow studies (like any spatial ecology exercise) should clearly state what resolution(s) they use and why.

Urbanization and plant diversity influence different aspects of floral phenology

Plant phenologies can shift as global temperatures rise and landscapes become human-dominated. Some of the most pronounced shifts in phenologies have been documented in urban areas, where surface temperatures can reach 5–7℃ warmer than surrounding rural areas. In this study, we examined how floral phenology—the initiation, peak, and duration of floral events — shifted in grasslands across an urbanization gradient in Louisville, Kentucky, a city with one of the most severe urban heat islands in the US. Our objectives were to understand (1) how urbanization influences floral phenology (2) whether high-quality habitats with increased habitat patch size and plant richness could offset some effects of urbanization, and (3) whether species responses varied across seasons. We found that average first date of flowering and peak abundance date occurred 1–2 weeks earlier in urban compared to rural areas. However, we found that floral duration was longest in sites with high plant richness, regardless of urbanization. We also found that summer-flowering species increased their floral duration in urban areas while spring and fall-flowering species shortened theirs. These differences in seasonal responses lead to an “urban summer spillage” effect where summer-flowering species are able to move into the temporal niche of spring and fall species in urban habitat patches. These shifts could lead to a reshuffling of communities and novel plant-plant competitive interactions or plant-animal interactions in the urban core, with lasting implications for urban conservation.

Rarity, geography, and plant exposure to global change in the California Floristic Province

AbstractAimRarity and geographic aspects of species distributions mediate their vulnerability to global change. We explore the relationships between species rarity and geography and their exposure to climate and land use change in a biodiversity hotspot.LocationCalifornia, USA.TaxaOne hundred and six terrestrial plants.MethodsWe estimated four rarity traits: range size, niche breadth, number of habitat patches, and patch isolation; and three geographic traits: mean elevation, topographic heterogeneity, and distance to coast. We used species distribution models to measure species exposure—predicted change in continuous habitat suitability within currently occupied habitat—under climate and land use change scenarios. Using regression models, decision‐tree models and variance partitioning, we assessed the relationships between species rarity, geography, and exposure to climate and land use change.ResultsRarity, geography and greenhouse gas emissions scenario explained &gt;35% of variance in climate change exposure and &gt;61% for land use change exposure. While rarity traits (range size and number of habitat patches) were most important for explaining species exposure to climate change, geographic traits (elevation and topographic heterogeneity) were more strongly associated with species' exposure to land use change.Main conclusionsSpecies with restricted range sizes and low topographic heterogeneity across their distributions were predicted to be the most exposed to climate change, while species at low elevations were the most exposed to habitat loss via land use change. However, even some broadly distributed species were projected to lose &gt;70% of their currently suitable habitat due to climate and land use change if they are in geographically vulnerable areas, emphasizing the need to consider both species rarity traits and geography in vulnerability assessments.

The impact of habitat loss on molecular signatures of coevolution between an iconic butterfly (Alcon blue) and its host plant (Marsh gentian).

Habitat loss is threatening natural communities worldwide. Small and isolated populations suffer from inbreeding and genetic drift, which jeopardize their long-term survival and adaptive capacities. However, the consequences of habitat loss for reciprocal coevolutionary interactions remain poorly studied. In this study, we investigated the effects of decreasing habitat patch size and connectivity associated with habitat loss on molecular signatures of coevolution in the Alcon blue butterfly (Phengaris alcon) and its most limited host, the marsh gentian (Gentiana pneumonanthe). Because reciprocal coevolution is characterized by negative frequency-dependent selection as a particular type of balancing selection, we investigated how signatures of balancing selection vary along a gradient of patch size and connectivity, using single nucleotide polymorphisms (SNPs). We found that signatures of coevolution were unaffected by patch characteristics in the host plants. On the other hand, more pronounced signatures of coevolution were observed in both spatially isolated and in large Alcon populations, together with pronounced spatial variation in SNPs that are putatively involved in coevolution. These findings suggest that habitat loss can facilitate coevolution in large butterfly populations through limiting swamping of locally beneficial alleles by maladaptive ones. We also found that allelic richness (Ar) of the coevolutionary SNPs is decoupled from neutral Ar in the butterfly, indicating that habitat loss has different effects on coevolutionary as compared with neutral processes. We conclude that this specialized coevolutionary system requires particular conservation interventions aiming at generating a spatial mosaic of both connected and of isolated habitat to maintain coevolutionary dynamics.

Size and degree of protection of native forest remnants drive the local occupancy of an endangered neotropical primate.

Although the species-area relationship is well known, it may interact with and be augmented or cancelled out by other factors, such as local human disturbance. We used data on site occupancy of the Endangered blonde capuchin monkey (Sapajus flavius) based primarily on a standardized program of local interviews to model the influence of past human disturbance on the occurrence of this species across remaining forest patches of northeastern Brazil within the Atlantic Forest and Caatinga biomes. To do so, we assessed environmental covariates that best represent the history of human impacts. We then used single-species occupancy models to assess site occupancy, while controlling for detection error during sampling. Surprisingly, we obtained a higher occupancy rate in the more arid Caatinga remnants than in the more mesic Atlantic Forest. Habitat patch size, history of site protection, and annual precipitation were the best predictors of local occupancy. Historical human disturbance, including subsistence hunting, has exerted considerable impact on the modern distribution of the blonde capuchin, whose geographic range largely spans a region historically lacking any wildlife protection. Matrix vegetation structure across the Caatinga, which so far has averted large-scale mechanized agriculture, also creates a benign landscape that likely benefits contemporary capuchin occupancy. Local extinctions of this endangered primate will most likely continue unabated unless a ban on hunting in remaining Atlantic Forest and Caatinga fragments can be enforced.

Habitat selection of black grouse in an isolated population in northern Germany-the importance of mixing dry and wet habitats.

Wildlife habitats in general must provide foraging, hiding and resting places as well as sites for reproduction. Little is known about habitat selection of black grouse in the lowlands of Central Europe. We investigated habitat selection of seven radio tagged birds in an open heath and grassland area surrounded by dense pine forests in the northern German Lüneburg Heath Nature Reserve. This site carries one of the last remaining populations in the Central European lowlands. Using resource selection functions based on presence/background data, we estimated the probability of black grouse occurrence by availability of, or distance to habitat types as well as vegetation diversity indices. Black grouse preferred undisturbed and heterogeneous habitats far from dense forests with wide sand heaths, natural grasslands and intermixed bogs, diverse vegetation and food sources, low density of (loose) shrub formations and solitary trees. Wetlands were extremely important in a landscape that is dominated by dry heaths and grasslands. About 4% (9 km2) of the nature reserve was a suitable habitat for black grouse, mostly due to lack of open areas due to the amount of dense forest, and because smaller, open heaths are only partly suitable. We suggest that to improve habitat quality and quantity for the grouse, habitat patch size and connectivity must be increased, along with a mosaic of heterogeneous landscape structures in these habitat islands. Our results may be used to inform and improve black grouse habitat management in the region and elsewhere.

Small giants: Tributaries rescue spatially structured populations from extirpation in a highly fragmented stream

Abstract Habitat fragmentation is a pervasive threat to biodiversity. Linearly arranged habitats such as stream networks are particularly vulnerable to fragmentation. As the landscape becomes increasingly human dominated, conservation values of fragmented habitat patches cannot be overlooked. It is critical to understand the demographic mechanisms of population persistence or extirpation in fragmented patches. We studied dynamics of spatially structured populations of two Japanese landlocked salmonids persisting for &gt;30 years in a headwater stream network that is highly fragmented due to low‐head dams in the mainstem. We parameterised and analysed spatial matrix population models using 9‐year mark–recapture data. Tributaries supported higher survival rates in some life stages, and movement was asymmetrical from the tributaries to the mainstem. Accordingly, population growth rates were higher in the tributary patches than the mainstem in both species despite the tributaries occupying only 12% or 18% of the study stream network by surface area. The tributaries harboured more physically and hydraulically complex instream habitats (i.e. higher wood density and flow refugia), indicating that habitat patch quality was more important than habitat patch size in determining the dynamics of these spatially structured populations. Tributary locations in the stream network were important in the trajectory of these populations. The upstream‐dwelling charr persisted in the highly fragmented mainstem patch (i.e. six impassable infrastructures in a &lt;500 m patch) due to immigration of fish from upstream including the tributary. However, the downstream‐dwelling salmon has been gradually extirpated from the uppermost section of the fragmented mainstem patch because they could not maintain a positive population growth rate after loss of emigrants was accounted for and immigration was prevented due to fragmentation. Synthesis and applications. We conclude that small tributaries have rescued the spatially structured populations from extirpation (charr) or at least slowed down extirpation (salmon). Legal protection of headwaters as aquatic habitats is weak globally. Our results suggest that stream management plans underestimating the demographic value of small tributaries will likely fail to conserve populations of headwater inhabitants and therefore endanger aquatic biodiversity. We discuss conservation implications of this study related to habitat connectivity and fisheries management.

Reduced fire frequency over three decades hastens loss of the grassy forest habitat of an endangered songbird

Fire plays an important role in maintaining grassy forests, and reduced fire frequency has been linked to encroachment of woody plants into grassy forests and woodlands globally. In Australia a range of threatened animals, including the northern population of the endangered eastern bristlebird (Dasyornis brachypterus), are dependent on grassy forests. We examined this issue by collating three decades of detailed monitoring and fire data for 43 current and historically-occupied bristlebird sites, and examined the relationships among fire history, bristlebird occupancy and habitat patch size/condition. Habitat patch size declined by over 50% between 1980 and 2009 due to woody plant encroachment. Bristlebird occupancy was associated with reduced habitat loss and time since fire, while reduced fire frequency was the main predictor of decline in grassy cover, a critical habitat element for bristlebirds. Our models suggested habitat loss was strongly influenced by fire history, particularly fire frequency, with reduced habitat loss associated with more-frequent burning. Native grass cover can return quickly, and remained high until 5–10 years post-fire; densest grass cover was found at sites with fire intervals of between 3.5 and 7 years. Active fire management, including regular ecological burning, is imperative for conservation of the eastern bristlebird and other threatened fauna that depend on these grassy forests. The massive changes in global patterns of fire currently occurring, and the threat this poses to biodiversity, make understanding the nuances of fire ecology, including the role of fire frequency, essential to improving conservation management.

Landscape configuration affects probability of apex predator presence and community structure in experimental metacommunities

Biodiversity is declining at an unprecedented rate, highlighting the urgent requirement for well-designed protected areas. Design tactics previously proposed to promote biodiversity include enhancing the number, connectivity, and heterogeneity of reserve patches. However, how the importance of these features changes depending on what the conservation objective is remains poorly understood. Here we use experimental landscapes containing ciliate protozoa to investigate how the number and heterogeneity in size of habitat patches, rates of dispersal between neighbouring patches, and mortality risk of dispersal across the non-habitat ‘matrix’ interact to affect a number of diversity measures. We show that increasing the number of patches significantly increases γ diversity and reduces the overall number of extinctions, whilst landscapes with heterogeneous patch sizes have significantly higher γ diversity than those with homogeneous patch sizes. Furthermore, the responses of predators depended on their feeding specialism, with generalist predator presence being highest in a single large patch, whilst specialist predator presence was highest in several-small patches with matrix dispersal. Our evidence emphasises the importance of considering multiple diversity measures to disentangle community responses to patch configuration.

Habitat specialisation and matrix resistance predict responses of butterfly populations to landscape features in tropical grassland-forest complexes.

A fundamental question in ecology is to understand how a species is distributed in a landscape. In terrestrial landscapes, the size and isolation of habitat patches, and matrix properties, are thought to drive population density patterns. Yet, given the same set of landscape features, why do species from a single taxon vary so widely in their density patterns? A primary hypothesis for such variation, proposed by community-level studies, is that key ecological characteristics of species influence how they respond to landscape features. However, robust tests of this hypothesis, which require measurements of populations of multiple species in an assemblage, are still scarce. We investigated the ability of ecological specialisation and the interaction of species with the matrix (matrix resistance) to predict population responses of butterfly species to patch size and connectivity in naturally heterogeneous tropical forest-grassland complexes. We surveyed 56 habitat patches in a 65 sq. km area by laying 276 transects, along which the identity and abundances of butterfly species were recorded. We also used transects that cut across two habitats to estimate matrix resistance. We find that habitat specialisation predicted the strength of area-density and isolation-density relationships. Matrix resistance also predicted variation in area-density relationships, highlighting the importance of species interactions with the matrix. Specialists showed higher matrix resistance and stronger area and isolation effects than did generalists. Our findings suggest that investigating how traits related to ecological specialisation and matrix resistance affect demographic parameters can contribute towards understanding mechanisms underlying species distributions in heterogeneous landscapes.

Density Dependent Refueling of Migratory Songbirds During Stopover Within an Urbanizing Coastal Landscape

Refueling performance is the primary currency of a successful migration as birds must maintain energy stores to achieve an optimal travel schedule. Migrating birds can anticipate heightened energy demand, not to mention increased uncertainty that energy demands will be satisfied, especially within an urbanizing landscape following long-distance flights. We tested the expectation that refueling performance of songbirds is reduced as densities increase at stopover sites in an urbanizing coastline of the Gulf of Mexico. We measured the density of migrating birds, their refueling performance, and arthropod abundance in two large tracts of contiguous forest paired with two small isolated patches embedded within residential settings throughout spring migration over the course of 2 years. Refueling performance declined with increasing migrant densities, even though the overall daily densities of birds stopping in these landscapes were relatively low and arthropod densities were low throughout. Habitat patch size alone did not account for differences in refueling performance, but smaller habitat patches more often concentrated migrants in higher densities where they experienced reduced refueling performance. We found support for density-dependent refueling performance during spring migration through a region where overall passage and stopover densities are low; suggesting that larger contiguous forest tracks within urban landscapes provide higher quality habitat for refueling and that effect is likely even more pronounced in landscapes within higher density migratory corridors. The nutritional challenges encountered during migration influence the overall pace of migration and changes in access to food resources due to increasing urbanization may ultimately impact optimal travel schedules.