Biodiversity In Fragmented Landscapes Research Articles

Habitat Fragmentation Affects Richness—A View Through a Metacommunity Lens

Habitat fragmentation is often assumed to negatively impact species diversity because smaller, more isolated populations on smaller habitat patches are at a higher extinction risk. However, some empirical and theoretical studies suggest that landscapes with numerous small habitat patches may support higher species richness, although the circumstances remain elusive. We used an agent-based metacommunity model to investigate this and simulate landscapes of the same total area but diverse patch sizes. Our model, as generic and unbiased by specific assumptions as possible, aimed to explore which circumstances may be more conducive to supporting higher biodiversity. To this end, most parameters and behaviors were random. The model included generalized species traits, dispersal, and interactions to explore species richness dynamics in fragmented landscapes of distinct patch sizes. Our results show that landscapes with many small patches maintain higher species richness than those with fewer large patches. Moreover, the relationship between patch connectivity and species richness is more pronounced in landscapes with smaller patches. High connectivity in these landscapes may support species diversity by preventing local extinctions and facilitating recolonization. In contrast, connectivity is less significant in large-patch landscapes, where generalist species dominate. The findings highlight the complex interplay between patch size quality, connectivity, species traits, and diverse interactions among species in determining species richness. We suggest the patterns produced by the model represent null predictions and may be useful as a reference for a diversity of more specialized questions and predictions. These insights may also have specific implications for conservation strategies, suggesting that maintaining a mosaic of small, well-connected patches could enhance biodiversity in fragmented landscapes.

The travel speeds of large animals are limited by their heat-dissipation capacities.

Movement is critical to animal survival and, thus, biodiversity in fragmented landscapes. Increasing fragmentation in the Anthropocene necessitates predictions about the movement capacities of the multitude of species that inhabit natural ecosystems. This requires mechanistic, trait-based animal locomotion models, which are sufficiently general as well as biologically realistic. While larger animals should generally be able to travel greater distances, reported trends in their maximum speeds across a range of body sizes suggest limited movement capacities among the largest species. Here, we show that this also applies to travel speeds and that this arises because of their limited heat-dissipation capacities. We derive a model considering how fundamental biophysical constraints of animal body mass associated with energy utilisation (i.e., larger animals have a lower metabolic energy cost of locomotion) and heat-dissipation (i.e., larger animals require more time to dissipate metabolic heat) limit aerobic travel speeds. Using an extensive empirical dataset of animal travel speeds (532 species), we show that this allometric heat-dissipation model best captures the hump-shaped trends in travel speed with body mass for flying, running, and swimming animals. This implies that the inability to dissipate metabolic heat leads to the saturation and eventual decrease in travel speed with increasing body mass as larger animals must reduce their realised travel speeds in order to avoid hyperthermia during extended locomotion bouts. As a result, the highest travel speeds are achieved by animals of intermediate body mass, suggesting that the largest species are more limited in their movement capacities than previously anticipated. Consequently, we provide a mechanistic understanding of animal travel speed that can be generalised across species, even when the details of an individual species' biology are unknown, to facilitate more realistic predictions of biodiversity dynamics in fragmented landscapes.

Optimising sampling designs for habitat fragmentation studies

Abstract Habitat fragmentation has become one of the largest areas of research in conservation biology. Empirical studies into habitat fragmentation impacts typically measure ecological responses to metrics describing fragmentation processes, for example ‘distance to the nearest forest edge’, ‘forest fragment area’ and ‘landscape habitat amount’. However, these studies often fail to sample across representative ranges of fragmentation metrics characterising the study region. They therefore lack the data to account for correlation among multiple fragmentation metrics and for spatial autocorrelation among sample sites, which reduces the strength of derived predictive models. Here, we draw on approaches used in the mining and soil science industry to develop standardised and repeatable protocols for designing optimised sampling schemes of biodiversity in fragmented landscapes that meet three criteria: the distance between sample sites is maximised to reduce spatial autocorrelation, the full range of values of the metrics of interest are sampled and the confounding effects of correlated metrics are minimised. We show that our computational methods can optimise the placement of sample sites in fragmented landscapes to minimise, and in some cases to entirely avoid, over‐ or under‐sampling of fragmentation metrics. Our method is flexible enough to cater for any continuous (e.g. maps of percentage tree cover) or categorical (e.g. habitat and land use types) fragmentation metric, and to simultaneously handle combinations of multiple fragmentation metrics and habitat types. We implement our methods as open‐source code which includes options to mask invalid or inaccessible regions, update designs to adapt to unforeseen constraints in the field and suggest optimal numbers of sample sites for given design criteria. Using a case study landscape, we demonstrate how the approach improves on manually generated sampling designs. We also show that the methods are flexible enough to be applied to landscape studies beyond the field of habitat fragmentation. We introduce our package as a novel research tool that is able to streamline the experimental design process for biodiversity sampling and monitoring at landscape scales, leading to improved data quality and representativeness.

Mixing of tree species is especially beneficial for biodiversity in fragmented landscapes, without compromising forest functioning

Abstract Contemporary forest management strives to satisfy contrasting demands on forest ecosystems by promoting multiple ecosystem services. These services are affected in varied manners by alternative management actions operating at local or landscape scales, potentially leading to trade‐offs and synergies that may impede or encourage forest managers to change practices. We here studied ecosystem functions and biodiversity across trophic levels in 53 mature forest plots varying in stand‐level (tree species composition) and landscape‐level (degree of fragmentation) characteristics. The consequences of tree species composition and forest fragmentation for the provision of forest ecosystem services were explored using desirability scores, contrasting two different perspectives on forest management: a conservationist perspective placing more value on biodiversity conservation and a productivist perspective attaching more value to timber production and natural forest regeneration. These scores were derived at two spatial scales distinguishing between ecosystem functions and forest biodiversity. We show that more than two thirds of the 20 trade‐offs and synergies between functions and diversity variables were driven by variation in tree species composition and fragmentation. While multifunctionality depended on the forest management perspective at the stand level, this dependence was no longer apparent at the landscape scale. Interestingly, more strongly fragmented landscapes had higher landscape‐level multifunctionality, but this came at the expense of biodiversity across trophic levels. At the same time, mixed forest stands had higher levels of biodiversity than monocultures without affecting multifunctionality. Synthesis and applications. In monocultures, it depends on the management perspective as to which tree species best maximizes multifunctionality. However, diversifying stands resolves this potential tension between different perspectives; in mixtures the level of multifunctionality no longer depended on the management perspective and similar levels were reached compared to the monocultures. Tree species mixtures also maximized biodiversity across trophic levels. Diversifying forest stands thus represents a promising management strategy that resolves potential trade‐offs between functioning and biodiversity.

Isolated trees support lower bird taxonomic richness than trees within habitat patches but similar functional diversity

AbstractLarge isolated trees are keystone structures that can help maintain biodiversity in fragmented landscapes, with evidence that open areas with isolated trees may support similar levels of taxonomic diversity to nearby patches of habitat. However, it is not clear if isolated trees can support the same diversity of ecological functions as trees in habitat patches. We compared species richness, community composition, and functional diversity of birds in trees at forest edges and isolated trees. Twenty isolated trees and ten edge trees of American muskwood (Guarea guidonia) were selected, and sampled on 11 occasions, each of 20 min, over four months. All individual birds that landed at trees were recorded using a standardized protocol. Species richness was, on average, almost twice as high at edge trees than at isolated trees. Taxonomic composition differed between edge and isolated trees, with many forest‐dependent birds restricted to edge trees, and some open‐area birds restricted to isolated trees. Overall functional diversity was similar at edge and isolated trees, but some ecological functions (e.g., frugivory) were less frequent, while others (e.g., granivory) were more frequent at isolated compared with edge trees. Isolated trees are important for supporting many ecological functions in modified areas. However, the maintenance of forest patches is essential to complement the provision of such functions in modified landscapes.Abstract in Portuguese is available with online material.

Quantifying factors for understanding why several small patches host more species than a single large patch

Several small habitat patches typically contain more species than a single large patch of comparable area. This pattern has fueled controversy over reserve design (the SLOSS debate); yet its causes remain poorly understood, limiting discussion of any broader biodiversity implications. Using 44 published faunal metacommunity datasets from fragments, islands and habitat islands, we test four hypotheses to explain differences in species richness (SRd) between several small patches and a single large patch: (i) beta diversity (BD); (ii) evenness of species abundance distributions (EV); (iii) size bias in sampling efficiency (SE); and (iv) taxonomy. We used individual-based null models and confirmatory path analysis to compare direct and indirect support for these non-exclusive hypotheses. Broad taxonomic grouping (invertebrates > birds = non-volant vertebrates) accounted for most of the variation in SRd, while BD, EV and SE had smaller, but comparable, direct effects (standardized coefficients = 0.42, 0.31 and −0.26 respectively). Within a taxonomic group, larger SRd occurred when both BD and EV increase. Although sampling bias probably overstates the difference in SRd, it does not explain the pattern. Beyond reserve design, the SLOSS pattern implies potential principles for managing biodiversity in fragmented landscapes. Whether this pattern should inform conservation requires greater understanding. We confirm beta diversity is the major contributor, but it is mediated by increases and decreases in evenness among small patches. Attention to how sub-division alters relative abundances (e.g., by biotic relaxation or altering competitive outcomes) might help clarify how the SLOSS pattern arises.

Multiscale analysis of canopy arthropod diversity in a volcanically fragmented landscape

AbstractHabitat fragmentation resulting in habitat loss and increased isolation is a dominant driver of global species declines. Habitat isolation and connectivity vary across scales, and understanding how connectivity affects biodiversity can be challenging because the relevant scale depends on the taxa involved. A multiscale analysis can provide insight in biodiversity patterns across spatial scale when information on dispersal ability is not available, in particular for community‐level studies focusing on multiple taxa. In this study, we examine the relationship between arthropod diversity, patch area, and connectivity using a multiscale approach. We make use of a natural experiment on Hawai‘i Island, where historic volcanic activity has transformed contiguous native forests to lava matrix and discrete forest patches. This landscape of patches has persisted for 150 yr, and we selected 10,000 ha consisting of 863 patches to analyze landscape connectivity using a graph theory approach. We collected arthropod samples from Metrosideros polymorpha tree canopies in 34 forest patches during multiple years. We analyzed the relationship of arthropod diversity with area, as well as with connectivity across increasing scales, or dispersal threshold distances. In contrast to well‐established ecological theory as well as prior work on birds and fungi in this system, we did not find support for a canonical species–area relationship. Next, we calculated connectivity across spatial scales and found lower Shannon diversity with higher connectivity at small scales, but no effect at increased dispersal threshold distances. We examined the landscape structure and found all habitat patches connected into three subnetworks at a 350 m threshold distance. All patches were connected at 700 m threshold distance, indicating structural dispersal limitation only at small scales. Our findings suggest that canopy arthropods are not dispersal limited at scales shown to impact both soil fungi and birds in this system. Instead, Hawaiian canopy arthropods may perceive the landscape as a connected area where discrete forest patches and the early‐successional matrix contribute resources that vary spatially with regard to habitat quality. We argue for the utility of multiscale approaches, and the importance of examining maintenance of biodiversity in fragmented landscapes that persist for hundreds of years.

The matrix matters, but how should we manage it? Estimating the amount of high‐quality matrix required to maintain biodiversity in fragmented landscapes

Improving matrix quality may be a powerful strategy for conserving biodiversity in fragmented landscapes, but effectively implementing this strategy requires a better understanding of how much of the matrix needs to be converted to ‘high‐quality’ land uses to achieve conservation goals. Here, we use data on the distribution of forest birds across > 1000 landscapes throughout New Zealand to quantify how the impacts of habitat loss (declining native forest cover) change as the proportion of matrix that is a high‐quality land use (exotic plantation forest) increases. As expected, we found that the amount of plantation forest in the matrix strongly influenced the extent to which native forest loss impacted bird communities: a decline in native forest cover from 90 to 1% caused a 60% decrease in bird species richness when there was no plantation forest in the matrix, but only a 15% decrease when 99% of the matrix was plantation forest. However, this plantation forest effect was strongly nonlinear, with most of the benefits of increasing plantation forest cover occurring before plantations reached even 10% of the matrix. Conversely, increasing plantation forest cover had minimal effects when the matrix was already dominated by plantation forest, or when native forest cover was high. Previous research has confirmed that matrix quality can strongly influence the biodiversity of fragmented landscapes, but results from our study system suggest that managing the matrix to benefit biodiversity could be surprisingly straightforward. Most of these benefits may be achieved by maintaining a small proportion of the matrix as high‐quality land uses.

Erratum to: Habitat fragmentation and biodiversity conservation: key findings and future challenges

Landscape Ecol DOI 10.1007/s10980-015-0312-3 EDITORIAL Habitat fragmentation and biodiversity conservation: key findings and future challenges Maxwell C. Wilson . Xiao-Yong Chen . Richard T. Corlett . Raphael K. Didham . Ping Ding . Robert D. Holt . Marcel Holyoak . Guang Hu . Alice C. Hughes . Lin Jiang . William F. Laurance . Jiajia Liu . Stuart L. Pimm . Scott K. Robinson . Sabrina E. Russo . Xingfeng Si . David S. Wilcove . Jianguo Wu . Mingjian Yu Received: 5 November 2015 / Accepted: 7 November 2015 Springer Science+Business Media Dordrecht 2015 Habitat loss and fragmentation has long been consid- ered the primary cause for biodiversity loss and ecosystem degradation worldwide, and is a key research topic in landscape ecology (Wu 2013). Habitat fragmentation often refers to the reduction of continuous tracts of habitat to smaller, spatially distinct remnant patches, and habitat loss typically occurs concurrently with habitat fragmentation (Col- linge 2009). Although some habitats are naturally patchy in terms of abiotic and biotic conditions (Wu and Loucks 1995), human actions have profoundly fragmented landscapes across the word (Haddad et al. 2015), altering the quality and connectivity of habitats. Therefore, understanding the causes and conse- quences of habitat fragmentation is critical to preserv- ing biodiversity and ecosystem functioning. From May 4th to 10th, 2015, an International Workshop on Habitat Fragmentation and Biodiversity Conservation, held at the Thousand Island Lake, Zhejiang, China, discussed threats to biodiversity in fragmented landscapes and how fragmentation research can identify and help mitigate these threats. M. C. Wilson J. Wu School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA e-mail: mcwilso2@gmail.com P. Ding (&) J. Liu X. Si M. Yu (&) College of Life Sciences & Institute of Ecology, Zhejiang University, Hangzhou 310058, Zhejiang, China e-mail: dingping@zju.edu.cn X.-Y. Chen School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200214, China R. T. Corlett A. C. Hughes Centre for Integrative Conservation, Xishuangbanna Tropical Botanic Garden, Chinese Academy of Sciences, Menglun, Mengla 666303, Yunnan, China R. K. Didham School of Animal Biology, University of Western Australia, Perth, WA 6009, Australia R. K. Didham CSIRO Land and Water, Centre for Environment and Life Sciences, Perth, WA 6014, Australia M. Yu e-mail: fishmj202@hotmail.com R. D. Holt Department of Biology, University of Florida, Gainesville, FL 32611, USA M. Holyoak Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA G. Hu Department of Landscape Architecture, School of Civil Engineering and Architecture, Zhejiang University of Science and Technology, Hangzhou 310018, Zhejiang, China

Habitat fragmentation and biodiversity conservation: key findings and future challenges

Habitat loss and fragmentation has long been considered the primary cause for biodiversity loss and ecosystem degradation worldwide, and is a key research topic in landscape ecology (Wu 2013). Habitat fragmentation often refers to the reduction of continuous tracts of habitat to smaller, spatially distinct remnant patches, and habitat loss typically occurs concurrently with habitat fragmentation (Collinge 2009). Although some habitats are naturally patchy in terms of abiotic and biotic conditions (Wu and Loucks 1995), human actions have profoundly fragmented landscapes across the word (Haddad et al. 2015), altering the quality and connectivity of habitats. Therefore, understanding the causes and consequences of habitat fragmentation is critical to preserving biodiversity and ecosystem functioning. From May 4th to 10th, 2015, an International Workshop on Habitat Fragmentation and Biodiversity Conservation, held at the Thousand Island Lake, Zhejiang, China, discussed threats to biodiversity in fragmented landscapes and how fragmentation research can identify and help mitigate these threats. To meet these challenges, the Workshop had three goals. The first was to synthesize key findings in fragmentation science. Second was to identify important remaining research questions concerning the relationships between habitat fragmentation, biodiversity, and ecosystem functioning at local, regional, and global scales. Finally, we examined the unique roles of field-based fragmentation experiments in addressing these questions. The Workshop’s findings are relevant to the broader ecological community, and we present them here to stimulate research that will advance landscape ecology and conservation biology.

Species interactions regulate the collapse of biodiversity and ecosystem function in tropical forest fragments.

Competitive interactions among species with similar ecological niches are known to regulate the assembly of biological communities. However, it is not clear whether such forms of competition can predict the collapse of communities and associated shifts in ecosystem function in the face of environmental change. Here, we use phylogenetic and functional trait data to test whether communities of two ecologically important guilds of tropical birds (frugivores and insectivores) are structured by species interactions in a fragmented Amazonian forest landscape. In both guilds, we found that forest patch size, quality, and degree of isolation influence the phylogenetic and functional trait structure of communities, with small, degraded, or isolated forest patches having an increased signature of competition (i.e., phylogenetic and functional trait overdispersion in relation to null models). These results suggest that local extinctions in the context of fragmentation are nonrandom, with a consistent bias toward more densely occupied regions of niche space. We conclude that the loss of biodiversity in fragmented landscapes is mediated by niche-based competitive interactions among species, with potentially far-reaching implications for key ecosystem processes, including seed dispersal and plant damage by phytophagous insects.

Land-cover change dynamics and insights into ecosystem services in European stream riparian zones

Riparian zones, transitional environments between terrestrial and freshwater ecosystems, have been historically threatened in Europe by land reclamation and exploitation of their natural resources. These fragile environments deliver a large number of ecological and societal services, while simultaneously playing a key role in the maintenance of biodiversity in fragmented landscapes. At large scales, one of the clearest and most informative indicators of alteration of state and characteristics of ecological systems is land-cover change. A newly available European riparian zone distribution dataset and continental land-cover change information allowed us to obtain an unprecedented continental overview of riparian land conversion and associated drivers, as well as a broad indication of their loss of capacity to provide ecosystem services. The analysis shows that only 1.8% of riparian zones experienced land-cover changes in the period 2000–2006. The majority of riparian changes involved forest loss and forest regrowth due to forestry activities and, to a lesser extent, to fires. Approximately 9% of land-cover changes involved conversion to artificial and agricultural surface, with trajectories largely affecting their ecological integrity. Using land-cover proxy-based indicators we show that the loss of riparian zones’ capacity to support ecological integrity and ecosystem services was overall significantly higher than the proportion of converted surface. The methodological approach can be used to support the assessment of environmental policy targets, and for regional planning and management of riparian zones.

Grassland area determines beetle assemblage dissimilarity from surrounding floodplain forest

Patch size is known to affect biodiversity in fragmented landscapes, but is usually examined in systems where the surrounding matrix habitat is unfavourable. We examined beetle diversity in a floodplain ecosystem that is characterised by naturally occurring grassland patches within a dominant matrix of contrasting yet habitable forest. We asked whether differences in the beetle assemblage between grassland and forest vegetation depended on the area of the grassland patch, which is a function of its flooding frequency and duration: smaller grasslands tend to be higher on the floodplain and are flooded less often and for shorter periods than larger grasslands. We found a negative relationship between grassland area and beetle abundance and species richness, and a positive relationship between grassland area and compositional dissimilarity from the surrounding forest. As expected, we found an overall difference in composition between forest and grassland assemblages, with five beetle species more common in the grasslands. Our study indicates that floodplain grasslands not only support beetle assemblages that are distinct from the surrounding forest, but that assemblages from the larger grasslands are compositionally more distinct than those from smaller grasslands. A likely cause of this pattern is the reduced edge effects and greater environmental contrast between forest and large grasslands that may be exposed to greater variation in local climate. Ongoing changes to flood regimes and potential encroachment of forest plants may decrease grassland area in the future, which may reduce spatial heterogeneity in the insect community in this unique floodplain ecosystem.

Fast restoration of grassland vegetation by a combination of seed mixture sowing and low-diversity hay transfer

Technical reclamation of grasslands is a powerful tool for conserving biodiversity in fragmented landscapes. Plant material transfer and sowing seeds of local provenance are used most frequently to recover grassland vegetation in former croplands. The joint application of these methods is rarely used, although it has the potential to gain a predictable and directed vegetation development with effective early weed suppression. We studied the effectiveness of combining low diversity seed sowing and hay-transfer in weed suppression and recovery of perennial grassland vegetation in Hortobágy Puszta, Central-Europe, by testing the following hypotheses: (i) lower weed cover and biomass is expected in vegetation recovered by the joint method of sowing and hay transfer than by seed sowing only. (ii) With sowing and additional hay transfer a higher rate of establishment of Festuca species is expected than with sowing only. Our results supported both hypotheses. We found that the additional application of hay significantly accelerated the development of perennial grassland vegetation and provided a higher weed suppression rate in the first year and onwards in most plots than seed sowing only. A higher establishment rate was detected both in the cover and the biomass of perennial grasses including Festuca species in all plots with hay addition than with sowing only. Our results suggest that a combination of hay transfer and low diversity sowing may provide a cost-effective alternative to the more costly high-density sowing and if proper sources for high-diversity hay are available, it may replace high-diversity seed mixtures.

Traditional home-garden conserving genetic diversity: a case study of Acacia pennata in southwest China

Conserving biodiversity in human-dominated systems requires research into mechanisms that can maintain biodiversity in fragmented landscapes. Home-garden as traditional agroforestry system in many regions has shown great value in maintaining a wide range of species. Here we show that home-garden populations are also capable of maintaining high level of genetic variation. Using six polymorphic microsatellite DNA markers, we have genotyped 260 individuals of Acacia pennata, a popular wild vegetable in the tropical region of southeast Asia. Samples were collected from home-gardens and wild populations in Xishuangbanna, southwest China. Microsatellite DNA diversity in planted populations were compared with that in geographically nearby wild populations with similar population size. Over 90 % of microsatellite genetic variation in wild populations was also present in planted populations. Pairwise comparison of planted and adjacent wild population showed no significant difference in allelic diversity and heterozygosity. Analysis revealed no significant genetic differences between wild and planted populations, while four home-garden populations showed sign of bottleneck. We conclude that home-gardens show great promise in maintaining genetic diversity, and that these managed patches could be of significant conservation value in tropical regions.

Do railway edges provide functional connectivity for plant communities in an urban context?

Functional connectivity is essential to maintaining biodiversity in fragmented landscapes but little attention has been given to structures that can provide it in an urban context. Using both the taxonomic and functional diversity of semi-natural grassland plant communities, we assessed the functional connectivity of linear transportation infrastructures in urban landscape. We sampled the vegetation at 71 study sites located along the edges of two railway lines. We hypothesised that if railways favour functional connectivity, then spatially connected communities should be more similar than disconnected communities. Therefore, we compared floristic dissimilarities between site pairs that were either connected or separated by a railway spatial break (overpass or station). As a further approach, we supposed that functional connectivity may attenuate the effect of urbanisation filters on plant communities. Thus we examined whether and how edges’ plant communities were influenced by urbanisation and compared our results to the patterns described in the literature. Functional connectivity was mainly maintained at railway stations, contrary to overpasses, which seemed to interrupt dispersal, demonstrating that railway edges provide connectivity for some but not all functional groups: this was only true for moderately mobile species. Surprisingly, railway edges did not seem to play an additional connective function for invasive species, the presence of which being strongly related to the urbanisation intensity and not influenced by spatial breaks along railways. Our study thus highlights the potential function of railway edges as corridors for common grassland plants. Landscape managers should include railways in green networks to improve connectivity in urban landscapes.

Mixed-source reintroductions lead to outbreeding depression in second-generation descendents of a native North American fish

Reintroductions are commonly employed to preserve intraspecific biodiversity in fragmented landscapes. However, reintroduced populations are frequently smaller and more geographically isolated than native populations. Mixing genetically, divergent sources are often proposed to attenuate potentially low genetic diversity in reintroduced populations that may result from small effective population sizes. However, a possible negative tradeoff for mixing sources is outbreeding depression in hybrid offspring. We examined the consequences of mixed-source reintroductions on several fitness surrogates at nine slimy sculpin (Cottus cognatus) reintroduction sites in south-east Minnesota. We inferred the relative fitness of each crosstype in the reintroduced populations by comparing their growth rate, length, weight, body condition and persistence in reintroduced populations. Pure strain descendents from a single source population persisted in a greater proportion than expected in the reintroduced populations, whereas all other crosstypes occurred in a lesser proportion. Length, weight and growth rate were lower for second-generation intra-population hybrid descendents than for pure strain and first-generation hybrids. In the predominant pure strain, young-of the-year size was significantly greater than any other crosstype. Our results suggested that differences in fitness surrogates among crosstypes were consistent with disrupted co-adapted gene complexes associated with beneficial adaptations in these reintroduced populations. Future reintroductions may be improved by evaluating the potential for local adaptation in source populations or by avoiding the use of mixed sources by default when information on local adaptations or other genetic characteristics is lacking.

Metacommunity diversity depends on connectivity and patch arrangement in heterogeneous habitat networks

Connectivity is critical to the maintenance of biodiversity in fragmented landscapes, but its effects differ depending on the arrangement of linkages within a habitat network. Additionally, heterogeneity in habitat quality within the habitat network can alter patterns of diversity at local and regional scales in the metacommunity. Using a controlled experiment we examined the interactive effects of habitat connectivity, network form (linear vs square), and habitat patch quality on a moss-inhabiting microarthropod community. We fragmented moss habitat while controlling for habitat loss, and altered habitat patch quality by regulating moisture conditions in landscapes differing in patch arrangement. Habitat patch quality had a significant effect on patterns of species richness, extinction, abundance and biomass. The effects of network form on diversity were strongest in heterogeneous landscapes. Gamma and beta diversity were greatest in continuous and linear landscapes. However, linear habitat networks showed marked patch specific edge effects that were detrimental to diversity under heterogeneous conditions. We provide direct evidence that habitat network structure impacts species community properties through mass effects, that are most evident when heterogeneity in habitat patch quality is present within the network. We conclude that habitat quality at the individual patch level and the distribution of high-quality habitat within the network are important factors affecting biodiversity in metacommunities.

Seasonal differences in population-, ensemble- and community-level responses of bats to landscape structure in Amazonia

The amount (composition) and spatial arrangement (configuration) of forest patches in fragmented landscapes influence the accessibility, as well as the abundance and diversity of resources available to bats. Moreover, tropical fruit and insect abundance differ seasonally in response to changes in precipitation, and many bats in the family Phyllostomidae employ seasonal reproductive strategies. Because reproductive activities involve constraints on time and energy as well as increased nutritional demands, foraging behavior and home range size may differ between wet and dry seasons. Nonetheless, seasonal variation in response to landscape structure by bats has not been examined previously. Consequently, population-, ensemble- and assemblage-level responses of phyllostomids to landscape composition and configuration were quantified separately during the wet and dry season at three circular focal scales (1, 3 and 5 km radii) for 14 sites in fragmented lowland Amazon forest. Responses to landscape characteristics were scale-dependent, species-specific, and seasonal. Abundances of frugivores responded to landscape composition in the dry season and to landscape configuration in the wet season. Conversely, abundances of animalivores responded to landscape configuration in the dry season and to landscape composition in the wet season. Divergent responses to landscape structure between seasons suggest that variation in resource abundance and diversity play a significant role in structuring population-, ensemble- and assemblage-level patterns. As such, considerations of the effects of dietary flexibility and reproductive constraints on foraging strategies and habitat use may be important when designing management plans that successfully promote long-term persistence of biodiversity in fragmented landscapes.

Patterns of ancestry and genetic diversity in reintroduced populations of the slimy sculpin: implications for conservation

Reintroductions are a common approach for preserving intraspecific biodiversity in fragmented landscapes. However, they may exacerbate the reduction in genetic diversity initially caused by population fragmentation because the effective population size of reintroduced populations is often smaller and reintroduced populations also tend to be more geographically isolated than native populations. Mixing genetically divergent sources for reintroduction purposes is a practice intended to increase genetic diversity. We documented the outcome of reintroductions from three mixed sources on the ancestral composition and genetic variation of a North American fish, the slimy sculpin (Cottus cognatus). We used microsatellite markers to evaluate allelic richness and heterozygosity in the reintroduced populations relative to computer simulated expectations. Sculpins in reintroduced populations exhibited higher levels of heterozygosity and allelic richness than any single source, but only slightly higher than the single most genetically diverse source population. Simulations intended to mimic an ideal scenario for maximizing genetic variation in the reintroduced populations also predicted increases, but they were only moderately greater than the most variable source population. We found that a single source contributed more than the other two sources at most reintroduction sites. We urge caution when choosing whether to mix source populations in reintroduction programs. Genetic characteristics of candidate source populations should be evaluated prior to reintroduction if feasible. When combined with knowledge of the degree of genetic distinction among sources, simulations may allow the genetic diversity benefits of mixing populations to be weighed against the risks of outbreeding depression in reintroduced and nearby populations.