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While habitat loss is a major threat to species, the effects of habitat fragmentation independent of habitat loss (fragmentation per se) are debated. Metapopulation studies often assert negative fragmentation effects, but they do not measure fragmentation per se. We evaluate the effects of fragmentation per se (patch density) across 20 years of patch occupancy patterns of the Åland Islands Glanville fritillary butterfly, Finland, a famous model system in metapopulation studies. Fragmentation per se had mainly positive effects on patch occupancy, the proportion of years occupied per patch, and patch colonization, and negative effects on patch extinction. These results suggest that fragmentation per se does not threaten persistence of the Åland Islands Glanville fritillary butterfly. Our results support the growing body of research challenging the paradigm that habitat fragmentation per se is mostly negative for species, highlighting the value of small patches for species conservation.

Aim While habitat loss is a primary driver of biodiversity declines worldwide, the role of habitat fragmentation per se is inconclusive, but likely depends on the amount of habitat left in a landscape. Here we aimed to tease apart the effects of habitat amount (percentage of native cover) and a fragmentation metric (number of fragments) on species richness and total abundance. Taxon Native small mammals. Location South American Atlantic Forest biome. Methods Small mammal species richness and abundance were obtained from a published database for 96 localities (groups of sampling sites). We then defined circular 100 km2 landscapes centred on each locality. For each landscape, percentage of habitat cover and number of fragments were measured on time frames close to the sampling periods. Effects of habitat amount, fragmentation and their interaction were modelled considering all landscapes, and also within four classes of habitat cover: 0%–10%, 10%–30%, 30%–50%, and 50%–100%. Results Species richness was mainly affected by percentage of habitat cover, with a three‐fold effect size compared to fragmentation. Yet, in landscapes with <10% or ≥50% of remaining cover, fragmentation positively affected species richness. Total species abundance also increased towards more fragmented landscapes. At the species level, three of the 20 species considered increased in abundance with fragmentation, while four species decreased. Main conclusion Percentage of habitat cover was the main driver of species richness when the entire cover range is considered, but the secondary effects of fragmentation were strong at the extreme ends of this range. Adding habitat patches in landscapes with low cover, or promoting habitat heterogeneity in landscapes with high cover, may boost species richness. However, further increases in species richness following fragmentation in high‐cover landscapes are likely to correspond to disturbance‐adapted species. In addition, such positive effects of fragmentation cannot be presumed to apply to all assemblages and species as some species are negatively affected.

Aim: It is usually thought that habitat fragmentation acts negatively on species survival, and consequently, on biodiversity. Recent literature challenges whether habitat fragmentation per se affects species richness, beyond the effect of habitat area. Theoretical studies have suggested that fragmentation may matter most when the amount of available habitat is small or at intermediate levels. However, a recent review suggests that the effect of fragmentation on species richness is usually positive. Here, we dissect the richness-fragmentation relationship. What is the effect size? Does it depend upon the amount of habitat cover? How do individual species respond to fragmentation? Methods: Applying a macroecological approach, we empirically related avian richness and the probability of occurrence (pocc) of individual species to fragmentation (number of patches), after controlling for habitat amount in 991 landscapes, each 100-km², in southern Ontario, Canada. Results: Species richness was strongly related to total habitat amount, but habitat fragmentation had no detectable additional effect. Individual species' pocc related strongly to habitat amount. For some species, pocc also related secondarily to habitat fragmentation within landscapes. Logistic models revealed that pocc related significantly negatively to fragmentation after controlling for habitat amount for only ~13% of forest- and 18% of open-habitat species bird species. However, pocc related significantly positively to fragmentation for even greater proportions of species, including some red-listed species. Fragmentation effects were not stronger at low or intermediate levels of habitat amount within landscapes. Conclusion: In earlier studies, negative effects of isolation were observed at the patch level in experimental manipulations. However, at the landscape level, avian species richness in southern Ontario apparently responds primarily to habitat amount and negligibly to fragmentation. We argue that the evidence is inconsistent with the hypothesis that reducing habitat fragmentation per se would be an effective conservation strategy for birds at the landscape level.

Opportunities to conduct large-scale field experiments are rare, but provide a unique opportunity to reveal the complex processes that operate within natural ecosystems. Here, we review the design of existing, large-scale forest fragmentation experiments. Based on this review, we develop a design for the Stability of Altered Forest Ecosystems (SAFE) Project, a new forest fragmentation experiment to be located in the lowland tropical forests of Borneo (Sabah, Malaysia). The SAFE Project represents an advance on existing experiments in that it: (i) allows discrimination of the effects of landscape-level forest cover from patch-level processes; (ii) is designed to facilitate the unification of a wide range of data types on ecological patterns and processes that operate over a wide range of spatial scales; (iii) has greater replication than existing experiments; (iv) incorporates an experimental manipulation of riparian corridors; and (v) embeds the experimentally fragmented landscape within a wider gradient of land-use intensity than do existing projects. The SAFE Project represents an opportunity for ecologists across disciplines to participate in a large initiative designed to generate a broad understanding of the ecological impacts of tropical forest modification.

Aim Phenotypic shifts are commonly observed when animals face insular habitat change and may reflect ongoing stresses on individuals. However, the generality and the driving processes of this ‘island rule’ remain equivocal, notably in amphibians. Here, we investigate both morphological and dietary shifts in a frog using a mosaic of human‐created islands to assess the potential operating mechanisms underlying these phenotypic responses. Location Thousand Island Lake, China. Taxon The Chinese piebald odorous frog, Odorrana schmackeri. Methods We compared body size between insular and mainland populations and between sexes. We examined the potential underlying mechanisms regarding body size shifts using structural equation modelling (SEM). Finally, we analysed changes in diet composition and compared intersexual diet overlap between islands and mainland sites. Results We found insular dwarfism in female but not male frogs. Meanwhile, insular females also had smaller gape widths than mainland females after accounting for snout‐vent lengths (SVLs). According to SEMs, resource availability had a direct positive effect on body size. Finally, diet composition differed between the island and mainland populations but only in females. Males and females on islands exhibited greater overlaps in the diet. Main conclusions In contrast with most studies in amphibians, we found insular dwarfism rather than gigantism in females. The smaller gape width after accounting for SVL in insular females suggests potential changes in prey utilization or food availability on these human‐created islands. This notion is further supported by the differentiation of diet composition between island and mainland females. The higher diet overlap between sexes implies stronger intersexual competition for food resources after habitat fragmentation. Overall, we found rapid shifts in morphology and diet in frogs, which might result from habitat fragmentation in only 50 years and underscore the need to consider intersexual differences when assessing responses of species to anthropogenic disturbances.

Habitat transformation is one of the leading causes of changes in biodiversity and the breakdown of ecosystem function and services. The impacts of habitat transformation on biodiversity are complex and can be difficult to test and demonstrate. Network approaches to biodiversity science have provided a powerful set of tools and models that are beginning to present new insight into the structural and functional effects of habitat transformation on complex ecological systems. We propose a framework for studying the ways in which habitat loss and fragmentation jointly affect biodiversity by altering both habitat and ecological interaction networks. That is, the explicit study of \"networks of networks\" is required to understand the impacts of habitat change on biodiversity. We conduct a broad review of network methods and results, with the aim of revealing the common approaches used by landscape ecology and community ecology. We find that while a lot is known about the consequences of habitat transformation for habitat network topology and for the structure and function of simple antagonistic and mutualistic interaction networks, few studies have evaluated the consequences for large interaction networks with complex and spatially explicit architectures. Moreover, almost no studies have been focused on the continuous feedback between the spatial structure and dynamics of the habitat network and the structure and dynamics of the interaction networks inhabiting the habitat network. We conclude that theory and experiments that tackle the ecology of networks of networks are needed to provide a deeper understanding of biodiversity change in fragmented landscapes.

Ecologists have used a variety of comparative mensurative and manipulative experimental approaches to study the biological consequences of habitat fragmentation. In this paper, we evaluate the merits of the two major approaches and offer guidelines for selecting a design. Manipulative experiments rigorously assess fragmentation effects by comparing pre- and post-treatment conditions. Yet they are often constrained by a number of practical limitations, such as the difficulty in implementing large-scale treatments and the impracticality of measuring the long-term (decades to centuries) responses to the imposed treatments. Comparative mensurative studies generally involve substituting space for time, and without pre-treatment control, can be constrained by variability in ecological characteristics among different landscapes. These confounding effects can seriously limit the strength of inferences. Depending on the scale of the study system and how \"landscape\" is defined, both approaches may be limited by the difficulty of replicating at the landscape scale. Overall, both mensurative and manipulative approaches have merit and can contribute to the body of knowledge on fragmentation. However, from our review of 134 fragmentation studies published recently in three major ecological journals, it is evident that most manipulative and mensurative fragmentation experiments have not provided clear insights into the ecological mechanisms and effects of habitat fragmentation. We discuss the reasons for this and conclude with recommendations for improving the design and implementation of fragmentation experiments.

The concept of habitat fragmentation has become an important theme in conservation research, and it is often used as if fragmentation were a unitary phenomenon. However, the concept is ambiguous, and empirical studies demonstrate a wide variety of direct and indirect effects, sometimes with mutually opposing implications. The effects of fragmentation vary across organisms, habitat types, and geographic regions. Such a contrast between a schematic concept and multifaceted empirical reality is counterproductive. I analyzed the stabilization of the schematic view of fragmentation by the early 1980s, using a genealogical narrative as a methodological approach. The main assumptions behind the schematic view were: (1) fragments are comparable to oceanic islands; (2) habitats surrounding fragments are hostile to a majority of the organisms; and (3) natural pre-fragmentation conditions were uniform. The stabilization loop of this view was supported by the reduction of empirical research to species-area curve fitting, which always produced expected results. I present a model of the dynamics of fragmentation research that shows the schematic, island-biogeographic view as an \"intellectual attractor.\" Since the 1980s, the theoretical presuppositions of the schematic view have been challenged, and empirical research has become multifaceted. Fragments of a particular habitat type are viewed as elements in a heterogeneous landscape rather than \"islands\" surrounded by a hostile \"sea.\" However, the island metaphor is still used in conservation contexts in the shape of species-area curves. It is backed by a presupposition that human-influenced environments are essentially different from so-called \"natural\" environments, but this is unfounded. My suggestion is that our perspective should be broadened still further so that habitat fragmentation is viewed as a particular form of human-induced environmental degradation; I discuss both theoretical and practical implications of this suggestion.

I reviewed and reconciled predictions of four models on the effect of habitat fragmentation on the population extinction threshold, and I compared these predictions to results from empirical studies. All four models predict that habitat fragmentation can, under some conditions, increase the extinction threshold such that, in more fragmented landscapes, more habitat is required for population persistence. However, empirical studies have shown both positive and negative effects of habitat fragmentation on population abundance and distribution with about equal frequency, suggesting that the models lack some important process(es). The two colonization-extinction (CE) models predict that fragmentation can increase the extinction threshold by up to 60-80%; i.e., the amount of habitat required for persistence can shift from <5% of the landscape to >80% of the landscape, with a shift from completely clumped to completely fragmented habitat. The other two models (birth-immigration-death -emigration, or BIDE models) predict much smaller potential effects of fragmentation on the extinction threshold, of no more than a 10-20% shift in the amount of habitat required for persistence. This difference has important implications for conservation. If fragmentation can have a large effect on the extinction threshold, then alteration of habitat pattern (independent of habitat amount) can be an effective tool for conservation. On the other hand, if the effects of fragmentation on the extinction threshold are small, then this is a limited option. I suggest that the difference in model predictions results from differences in the mechanisms by which the models produce the extinction threshold. In the CE models, the threshold occurs by an assumed reduction in colonization rate with decreasing habitat amount. In the BIDE models, loss of habitat is assumed to increase the proportion of the population that spends time in the matrix, where reproduction is not possible and the mortality rate is assumed to be higher (than in breeding habitat). Habitat loss therefore decreases the overall reproduction rate and increases the overall mortality rate on the landscape. I hypothesize that this imposes a constraint on the potential for habitat fragmentation to mitigate effects of habitat loss in BIDE models. To date, empirical studies of the independent effects of habitat loss and fragmentation suggest that habitat loss has a much larger effect than habitat fragmentation on the distribution and abundance of birds, supporting the BIDE model prediction, at least for this taxon.

An important evolutionary hypothesis posits that much of the biodiversity we see today arose during episodes of natural habitat fragmentation through the interplay of colonization, extinction, adaptation, and speciation. To interrogate the generality of this hypothesis, we leverage the natural experiment provided by arthropod communities in kīpuka—patches of Hawaiian wet forest isolated by lava flows. With DNA metabarcoding, we provide the first simultaneous exploration of ecological and evolutionary characteristics in the kīpuka system. At both species‐equivalent (3% radius OTUs) and haplotype‐equivalent (zOTUs) scales, we find that richness increases with kīpuka area, and that kīpuka exhibit faster distance decay of similarity compared to continuous forest. Kīpuka also differ in OTU and zOTU composition from continuous forest, notably hosting higher proportions of non‐native OTUs for an arthropod order in which we can comprehensively classify native/non‐native OTUs (Araneae). These findings reveal that natural habitat fragmentation drives parallel changes at species and haplotype scales in the kīpuka system. By integrating ecological and evolutionary perspectives, our study underscores the importance of studying both processes simultaneously if we are to understand, better predict, and more intelligently manage the responses of biological communities to environmental change. Leveraging a natural experiment provided by arthopod communities in Hawaiian wet forest fragments isolated by lava flows, this study examines the impact of natural habitat fragmentation on species‐equivalent (3% radius OTUs) and haplotype‐equivalent (zOTUs) scales. The authors observe that fragments host distinct communities from native forest and experience higher rates of turnover, both at species‐ and haplotype‐equivalent scales. This system provides an exciting opportunity to test the idea of natural habitat fragments as “crucibles of evolution,” given that we find arthropods to be undergoing genetic differentiation while isolated in different biological communities.