The quality and isolation of habitat patches both determine where butterflies persist in fragmented landscapes

Habitat quality and metapopulation effects are the main hypotheses that currently explain the disproportionate decline of insects in cultivated Holarctic landscapes. The former assumes a degradation in habitat quality for insects within surviving ecosystems, the latter that too few, small or isolated islands of ecosystem remain in landscapes for populations to persist. These hypotheses are often treated as alternatives, and this can lead to serious conflict in the interpretations of conservationists. We present the first empirical demonstration that habitat quality and site isolation are both important determinants of where populations persist in modern landscapes. We described the precise habitat requirements of Melitaea cinxia, Polyommatus bellargus and Thymelicus acteon, and quantified the variation in carrying capacity within each butterfly's niche. We then made detailed surveys to compare the distribution and density of every population of each species with the size, distance apart and quality of their specific habitats in all their potential habitat patches in three UK landscapes. In each case, within-site variation in habitat quality explained which patches supported a species' population two to three times better than site isolation. Site area and occupancy were not correlated in any species. Instead of representing alternative paradigms, habitat quality and spatial effects operate at different hierarchical levels within the same process: habitat quality is the missing third parameter in metapopulation dynamics, contributing more to species persistence, on the basis of these results, than site area or isolation. A reorientation in conservation priorities is recommended.     

Developing a functional connectivity indicator to detect change in fragmented landscapes

Biodiversity indicators are increasingly used to assess progress towards conservation targets. Particular indicators are required to assess the impacts of habitat fragmentation on landscape connectivity and biodiversity value. This paper recognises that connectivity is best defined by the interaction between species and the landscape in which they occur, and proposes a functional approach to assess connectivity. The approach utilises an incidence function model (IFM) as a spatially explicit method to assess potential species-level connectivity. The standard IFM connectivity measure is modified to account for the influence of the surrounding landscape matrix on edge impacts (through a weighted internal edge buffer) and ecological isolation (through an assessment of least-cost distance to account for landscape permeability). It has been recognised that such patch-based connectivity measures can provide misleading results when used to examine change, as they only focus on between patch movements. As a result, a modified hybrid IFM, based on a combination of patch and cell-based approaches, is developed to account for both within (intra) and between (inter) patch connectivity. The resulting probability of functional connectivity (PFC) indicator was evaluated, alongside a patch-based connectivity measure, through the application to four model landscapes based on changes (2 negative and 2 positive) to a control landscape. The four model landscapes illustrate the impact of landscape change on habitat area, edge impacts and matrix permeability. The proposed PFC indicator successfully discriminated between the two negative and the two positive changes to the control landscape, whereas, the patch-based connectivity measure detected change successfully within three of the four landscapes. The PFC indicator predicted a decrease in intra and inter-patch connectivity following habitat loss and fragmentation (negative change 1), whereas patch-based connectivity measures indicate an increase in connectivity between fragmented patches. The proposed PFC indicator offers the opportunity to take the necessary species-based perspective to examine functional connectivity, incorporating habitat preference, dispersal probability, edge impacts and ecological isolation/permeability. The urgency to assess changes in connectivity and support conservation policy means that there is little time to wait for more complete data. We believe the proposed approach provides a robust balance between the data required and the biologically meaningful indicator produced.     

Habitat selection by Canada lynx: making do in heavily fragmented landscapes

Habitat loss and fragmentation result in landscapes where high quality habitat patches are surrounded by matrix habitats of low and variable quality. For mobile species to persist in such landscapes, individual animals often rely on the high quality habitats but also use matrix habitats for supplemental resources or while moving between higher quality patches. Determining what habitat features animals select when in these matrix areas is important, as retaining desirable features in lower quality habitats may enable species persistence. We examine a population of US federally threatened Canada lynx (Lynx canadensis) in northcentral Washington, near the southwestern range limit, where lynx habitat is fragmented by topography, wildfires, and human impacts. We used Global Positioning System radio-collar data from 17 lynx in the North Cascade Mountains during 2007–2013 to explore lynx habitat use. We used Random Forest models to analyze core hunting, resting, and denning habitat, and the habitats lynx select while between patches of core habitat. While selecting core habitat, lynx used spruce (Picea engelmannii)-fir (Abies lasiocarpa), lodgepole pine (Pinus contorta), and mixed sub-boreal-Douglas fir (Pseudotsuga menziesii) forests, and avoided dry forests and forest openings including new burns. When not in core habitat, lynx used a wider range of habitats, including new burns where fire skips and residual trees offered cover. Our results show clearly that Canada lynx tolerate a wider range of habitats where they occupy fragmented landscapes. Consequently, maintaining animals in fragmented landscapes requires that we identify and conserve not only the core habitats a particular species selects, but also the habitat features animals use while in less suitable environments.     

Habitat quality and connectivity in agricultural landscapes: The role of land use systems at various scales in time

Connectivity is a key concept of landscape ecology as it relates to flows and movements of organisms as driven by landscape structure. More and more aspects of landscape heterogeneity are considered in measuring connectivity, as the diversity of crops in agricultural landscapes. In this paper, we explored the value of considering changes and cumulated effects of connectivity over time. As an example, we analysed connectivity among patches influenced by maize over 7 years in an agricultural landscape in Brittany, France.Clear temporal patterns appeared: maize is concentrated in certain parts of the landscape, but over the period the whole area, 70% of the landscape, used for maize was connected. Instead of discrete patches, maize may produce large clusters allowing movement from patch to patch from year to year. This reinforces the importance of understanding land use allocation rules within farms and landscapes to evaluate the ecological effects of agriculture.     

Spatial pattern of habitat quality modulates population persistence in fragmented landscapes

Habitat quality is one of the important factors determining population dynamics and persistence, yet few studies have examined the effects of spatial heterogeneity in within-patch habitat quality. In this paper, we use a spatially explicit agent-based model to investigate how habitat fragmentation and spatial pattern of within-patch habitat quality affect population dynamics and long-term persistence. We simulate three levels of habitat fragmentation (ranges from continuous to highly fragmented) and three types of spatial patterns in habitat quality within patches (i.e., negatively autocorrelated, randomly distributed, and positively autocorrelated). Hypothetical species differ in their niche specialization. The results demonstrate explicitly that the spatial pattern of within-patch habitat quality plays an important role in modulating the effects of habitat fragmentation on populations. Populations become less variable in size, and experience lower probability of extinction in landscapes with positively autocorrelated within-patch habitat quality. Specifically, specialized species are more vulnerable to habitat fragmentation, but this vulnerability is greatly mitigated by positively autocorrelated habitat quality within patches, in other words, exhibiting higher resistance to habitat fragmentation. The findings of this study suggest that managing habitat quality in existing habitat remnants is important to preserve species in habitats undergoing fragmentation, particularly for those with specialized habitat requirements.     

Neutral communities in fragmented landscapes

Habitat fragmentation displays a crucial role in conservation biology. Despite this, little is known about the detailed ecological consequences of habitat fragmentation due to the scarce number of controlled experimental surveys. The species–area relationship, a fundamental concept in ecology, requires the understanding of the fragmentation effects in a long term perspective, which turns this task even harder. Here we address the spatial patterns of species distribution in fragmented landscapes, assuming a neutral community model. We study the species area relationship and how its shape changes as the landscape becomes more fragmented. Recent investigations, based on extensive computer simulation, have contributed to establish some definite conclusions in the study of non‐fragmented landscapes: the existence of a three‐regime or two‐regime scenario for the species–area relationship, the emergence of a power‐law regime at intermediate scales and the augment of the species–area exponent z with the speciation rate. Despite the recent efforts, some other questions remain, such as the dependence of z in the whole range of the speciation rate. Questions like these are currently debated but generalizations cannot be drawn. This is the first paper, to our knowledge, that uses the coalescence method and neutral theory to examine biodiversity on more complex spatial structures. Our simulation results corroborate that the fragmentation plays a crucial role in shaping the species–area relationship, by determining the existence and extension of the power‐law regime associated with small and intermediate areas. On the other hand, when individuals are allowed to disperse over longer distances the species–area relationship now displays the classic triphasic pattern, and the intermediate regime, which is well described by a power‐law, is established even for highly fragmented landscapes.     

Dispersal and extinction in fragmented landscapes

Evolutionary and population dynamics models suggest that the migration rate will affect the probability of survival in fragmented landscapes. Using data for butterfly species in the fragmented British landscape and in immediately adjoining areas of the European continent, this paper shows that species of intermediate mobility have declined most, followed by those of low mobility, whereas high-mobility species are generally surviving well. Compared to the more sedentary species, species of intermediate mobility require relatively large areas where they breed at slightly lower local densities. Intermediate mobility species have probably fared badly through a combination of metapopulation (extinction and colonization) dynamics and the mortality of migrating individuals which fail to find new habitats in fragmented landscapes. Habitat fragmentation is likely to result in the non-random extinction of populations and species characterized by different levels of dispersal, although the details are likely to depend on the taxa, habitats and regions considered.     

Habitat restoration will help some functional plant types persist under climate change in fragmented landscapes

In the next century, global climate change is predicted to have large influences on species' distributions. Much of the research in this area has focused on predicting the areas where conditions will be suitable for the species in future, and thus the potential distribution of the species. However, it is equally important to predict the relative abilities of species to migrate into new suitable areas as conditions shift, while accounting for dynamic processes, such as dispersal, maturation, mortality, and reproduction, as well as landscape characteristics, such as level of habitat fragmentation and connectivity. In this study, we developed a spatially explicit individual‐based model that addresses these factors. As a motivating case study, we based aspects of the model on southwest Australia, a global biodiversity hotspot, but stress that the results obtained are generalizable beyond this region. Using the model, we enhanced current understanding of climate change impacts by investigating how and to what extent the functional traits of plant species affect their ability to move with climate change across landscapes with various levels of fragmentation. We also tested the efficacy of strategic restoration, such as planting corridors to increase connectivity among fragments. We found that even if the landscape is fully intact, only an average of 34.2% of all simulated functional groups had a good chance of successfully tracking climate change. However, our study highlights the power of strategic restoration as a tool for increasing species persistence. Corridors linking fragments increased species persistence rates by up to 24%. The lowest persistence rates were found for trees, a functional group with high dispersal but also long generation times. Our results indicate that for trees intervention techniques, such as assisted migration might be required to prevent species losses.     

Patch-occupancy dynamics in fragmented landscapes

Recent work on the dynamics of species living In fragmented landscapes has produced much Information on patterns of habitat patch occupancy in a wide range of organisms. Building on an elementary Markov chain model of patch occupancy, a family of Incidence-function models can be constructed for particular kinds of metapopulations. These models can be parameterized with field data on patch occupancy, and the models can be used to make quantitative predictions about specific metapopulations. This approach provides a potentially powerful tool for the management of reserve networks and species living in fragmented landscapes.     

Contrasting effects of habitat quantity and quality on moth communities in fragmented landscapes

Habitat loss is commonly identified as a major threat to the loss of global biodiversity. In this study, we expand on our previous work by addressing the question of how lepidopteran species richness and composition vary among remnants of North American eastern deciduous forest located within agricultural or pastoral landscapes. Specifically, we tested the relative roles of habitat quantity (measured as stand area and percent forest in the greater landscape) and habitat quality (measured as tree species diversity) as determinants of moth species richness. We sampled >19 000 individuals comprising 493 moth species from 21 forest sites in two forested ecoregions. In the unglaciated Western Allegheny Plateau, the species richness of moths with woody host plants diminished as forest stand size and percent forest in the landscape decreased, but the total species richness and abundance of moths were unaffected by stand size, percent forest in the landscape, or tree species diversity. In contrast, the overall species richness and abundance of moths in the glaciated North Central Tillplain were affected primarily by tree species diversity and secondarily by forest size. Higher tree species diversity may reduce species loss from smaller forest stands, suggesting that small, diverse forests can support comparable numbers of species to those in less diverse, large stands. Smaller forests, however, contained a disproportionate number of moth species that possess larvae known to feed on herbaceous vegetation. Thus, although woody plant feeding moths are lost from forests with changes in stand area, new species appear capable of recolonizing smaller fragments from the surrounding habitat matrix. Our study further suggests that when species replacement occurs, local patch size and habitat quality may be more important than landscape context in determining the community structure of forest Lepidoptera.     

Forest-climate interactions in fragmented tropical landscapes

In the tropics, habitat fragmentation alters forest-climate interactions in diverse ways. On a local scale (less than 1 km), elevated desiccation and wind disturbance near fragment margins lead to sharply increased tree mortality, thus altering canopy-gap dynamics, plant community composition, biomass dynamics and carbon storage. Fragmented forests are also highly vulnerable to edge-related fires, especially in regions with periodic droughts or strong dry seasons. At landscape to regional scales (10-1000 km), habitat fragmentation may have complex effects on forest-climate interactions, with important consequences for atmospheric circulation, water cycling and precipitation. Positive feedbacks among deforestation, regional climate change and fire could pose a serious threat for some tropical forests, but the details of such interactions are poorly understood.     

Dispersal abilities and spatial patterns in fragmented landscapes

Recent theoretical studies suggest that the distribution of species in space has important implications for the conservation of communities in fragmented landscapes. Facilitation and dispersal are the primary mechanisms responsible for the formation of spatial patterns. Furthermore, disruptions in the formation of patterns arise after degradation, which can serve as an early indicator of stress in plant communities. Spatial dispersal ability and pattern formation were evaluated in 53 linear transects of 500 m in length within 14 fragments of natural vegetation within a matrix of abandoned crop fields in Cabo de Gata National Park, Almería, Spain. Fragments were classified into three size classes (< 300, 300–900, and > 900 ha). Fragment connectivity was quantified using the distances between fragments. Spatial dispersal ability was quantified for the 187 species recorded in the study. Species with restricted dispersal had the highest degree of long‐range spatial autocorrelation and, species that disperse by biotic vectors (e.g. vertebrates), the lowest. In addition, species most susceptible to fragmentation are vertebrate‐dispersed shrubs, which declined in abundance and was associated with loss of spatial organization in the smallest fragments. It is postulated that the positive feedback between abundance of recruitment and vertebrate visits influences the colonization and persistence of vertebrate‐dispersed shrubs, explaining its abundance in large fragments. Indeed, fragments lower than a certain threshold reduced spatial organization not only in shrubs with biotic dispersal, but also in species with abiotic dispersal (mainly wind) and with restricted dispersal. Fragments lower than a certain threshold may be vulnerable to a cascade of species loss because of reduced recruitment, establishment and patch biomass as a result of natural senescence, finally breaking up facilitative plant interactions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 935–947.     

Making statistics biologically relevant in fragmented landscapes

The biological impacts of habitat fragmentation are routinely assessed using standard statistical modelling techniques that are used across many ecological disciplines. However, to assess the biological relevance of fragmentation impacts, we must consider an extra, spatial dimension to the standard statistical model: the biological importance of a significant and well supported model with large effect sizes crucially depends on the configuration of habitat within the study area. We argue that mapping the outputs from statistical models across a study area generates biologically meaningful estimates of fragmentation impacts. Integrating traditional statistical approaches with geographic information systems will facilitate rigorous comparisons of fragmentation impacts between taxa, studies and ecosystems.     

Habitat quality and population density drive occupancy dynamics of snowshoe hare in variegated landscapes

The influence of habitat quality and population density on occupancy dynamics may surpass that of traditional metrics of area and isolation, but often this is not considered explicitly in studies of spatially structured populations. In landscapes that are not easily characterized as binary habitat/non‐habitat (e.g. variegated landscapes), this influence may be even more important and occur at both local and landscape levels. It follows that occupancy dynamics may be driven by disparate processes depending on how extinction or colonization relate to habitat quality and population density. We examined the relative influence of area, structural isolation, habitat quality, local population density, and neighborhood population density (i.e. population density in the landscape around a site) on the probability of extinction and colonization of snowshoe hare Lepus americanus across an expansive forest mosaic landscape (encompassing the northern third of Idaho). Habitat quality and population density were highly influential in determining extinction and colonization, whereas patch area and isolation were much less important. Sites with heavier vegetative cover at the site or landscape‐level were more likely to be colonized and less likely to go extinct, and sites with greater local population density in the previous time step had lower probability of extinction. Sites embedded in high density neighborhoods also were less likely to go extinct, but not more likely to be colonized. We found a significant interaction between local and neighborhood population density on extinction in 1 yr, suggesting that the strength of demographic rescue may vary dependent on local site densities. Our results add to a growing literature showing that factors outside of structural metrics of area and isolation are important drivers of occupancy dynamics. Given the multi‐scaled influence of habitat quality and population density on occupancy dynamics, our work also indicates that research on snowshoe hare must extend beyond simply assessing local factors to understand the spatial dynamics of populations.     

Artificial canopy bridges improve connectivity in fragmented landscapes: The case of Javan slow lorises in an agroforest environment

Canopy bridges are increasingly used to reduce fragmentation in tropical habitats yet monitoring of their impact on the behavior of primates remains limited. The Javan slow loris (Nycticebus javanicus) is endemic to Java, Indonesia, where the species most often occurs in human-dominated, highly patchy landscapes. Slow lorises cannot leap, are highly arboreally adapted, and are vulnerable on the ground. To increase arboreal connectivity, as part of a long-term conservation project in Cipaganti, West Java, we built and monitored seven slow lorises bridges of two types—waterline or rubber—and monitored their use by seven adult individuals from 2016 to 2017. Motion triggered camera traps collected data for 195 ± standard deviation (SD) 85 days on each bridge. We collected 341.76 hr (179.67 hr before and 162.09 hr after the installation of bridges) of behavioral and home range data via instantaneous sampling every 5 min, and terrestrial behavior (distance and duration of time spent on the ground) via all occurrences sampling. We found that slow lorises used bridges on average 12.9 ± SD 9.7 days after their installment mainly for traveling. Slow lorises showed a trend toward an increase in their home range size (2.57 ha before, 4.11 ha after; p = 0.063) and reduced ground use (5.98 s/hr before, 0.43 s/hr; p = 0.063) after implementation of bridges. Although the number of feeding trees did not change, new feeding trees were included in the home range, and the proportion of data points spent traveling and exploring significantly decreased (p = 0.018). Waterline bridges serve a purpose to irrigate the crops of local farmers who thus help to maintain the bridges, and also ascribe value to the presence of slow lorises. Other endemic mammal species also used the bridges. We advocate the use and monitoring of artificial canopy bridges as an important supplement for habitat connectivity in conservation interventions.     

Distribution and abundance of dung beetles in fragmented landscapes

Related species utilising similar resources are often assumed to show similar spatial population structures and dynamics. This paper reports substantial ecological variation within a set of Aphodius dung beetles occurring in the same patchily distributed resource, livestock dung in pastures. We show how variation in habitat and resource selectivity, in the rate of movements between pastures, and in the distribution of local population sizes all contribute to interspecific differences in spatial population structures. Local dung beetle assemblages are compared between two landscapes with different densities of pastures. In one of the landscapes, we contrast the abundances and regional distributions of Aphodius before and after 15 years of rapid habitat loss. Different species show very dissimilar responses to changes in the structure of the landscape. Our results suggest that generalist Aphodius species, and specialist species with high dispersal powers, occur as large "patchy" populations in the landscape. In contrast, a strict pasture specialist species with limited dispersal powers (A. pusillus) forms classical metapopulations. At the community level, interspecific differences in spatial population structures make the local community composition a function of the structure of the surrounding landscape.     

Finding habitat patches and directional connectivity

For animal species inhabiting patchy environments, the search behavior of individuals and the distance from which they can detect suitable habitat (perceptual range) are key determinants of the functional connectivity of landscapes. We examined the movement behavior and perceptual range of adult cactus bugs ( Chelinidea vittiger ), which are habitat specialists that feed and reproduce on Opuntia cactus. Movement pathways of walking individuals released into unsuitable matrix habitat (30–3000 m from Opuntia ) were highly directional. These results supported predictions of optimal search behavior from published simulation models. A release experiment within natural patch networks indicated that the perceptual range of C. vittiger depended on size of the target patch, matrix structure, and direction of the target patch relative to prevailing winds. A strong effect of wind direction on orientation behavior (and presumed perceptual range) was evident in a release experiment using 'artificial' patches of potted Opuntia . In these two experiments, individuals released 50–100 cm from Opuntia patches were more likely to orientate toward patches located upwind than to those located crosswind or downwind. A reexamination of the pathways of individuals walking in the matrix also revealed a strong bias for movement upwind. Such upwind movement by individuals, both within and outside of patch networks, suggests that C. vittiger uses olfaction to navigate and it complicates our ability to interpret search behavior and to estimate perceptual range. Current techniques for assessing perceptual range have limitations for olfactory-based species. Furthermore, we need to broaden our view of perceptual range and of patch and landscape connectivity. Perceptual range may be anisotropic and connectivity may be directional. An organism-based approach to spatial ecology requires that we consider the dominant senses used by species when navigating around patchy landscapes.     

Effects of habitat configuration and quality on species richness and distribution in fragmented forest patches near Rome

Question: How important are habitat configuration, quality, history and anthropic disturbance in determining nemoral plant species richness and distribution of fragmented forest patches in a Mediterranean region? Location: Agricultural landscape north of Rome, Italy. Methods: Sixty‐nine woodland patches, identified through a stratified random sampling, were sampled for nemoral plant species. The homogeneity of woodlands was tested through a hierarchical classification of the floristic data and a Mann‐Whitney test of dependent and independent variables. The importance of habitat configuration (area, isolation, shape), quality (soil properties, forest structure, anthropic disturbance) and history (age of woodland) in determining species richness was estimated through a Poisson regression model. Presence‐absence of each species was analysed by logistic regression. Differences among plant life‐trait types (life span, dispersal mode, habitat preference) were analysed by comparing their median β‐values through ANOVA models. Results: Through hierarchical classification, two woodland types were identified that differed in species composition, habitat quality and spatial configuration. Poisson regression showed that habitat configuration and history influenced species richness. Multiple logistic regression resulted in significant fits for 88 species/variable combinations: 38 are habitat quality variables, 25 are habitat configuration variables, and 13 are anthropic factors. Dispersal strategies varied significantly with respect to area, isolation and age, while generalist and specialist species differed according to age of the woodland. Conclusion: Our results show that habitat history and configuration are the key factors determining species richness of woodland. Together with habitat configuration, habitat quality (mainly soil acidity) appeared to influence species composition.