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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.

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.

ContextAn important part of landscape ecology is to identify relationships between landscape characteristics and ecological processes. One common approach to this is relating raster surfaces to ecological responses, assuming that the characteristics emphasized by rasters are representative of the processes determining changes in the ecological responses being assessed. Consequently, choices made in the design and assessment of rasters affect our understanding of the relationship between landscape characteristics and ecological responses.ObjectivesWe propose a six-step framework for informing the choices made in creating and measuring rasters for landscape analyses: (i) acknowledge ecological theory and conceptual paradigms, (ii) evaluate the fit of available data, (iii) assess the three facets of scale, (iv) recognize different sampling designs, (v) use proper conceptual models, and (vi) measure meaningful raster characteristics.ConclusionsWe discuss how each step can benefit from a “functional” perspective, i.e., an explicit focus on the ecological processes under investigation. This is especially important for landscape analyses of habitat change, which are highly complex due to the many processes potentially involved. A functional perspective draws attention to common pitfalls in landscape ecology, while promoting more process-oriented research in the study of habitat change.

Animal pollination is essential for the reproductive success of many wild and crop plants. Loss and isolation of (semi-)natural habitats in agricultural landscapes can cause declines of plants and pollinators and endanger pollination services. We investigated the independent effects of these drivers on pollination of young cherry trees in a landscape-scale experiment. We included (i) isolation of study trees from other cherry trees (up to 350 m), (ii) the amount of cherry trees in the landscape, (iii) the isolation from other woody habitats (up to 200 m) and (iv) the amount of woody habitats providing nesting and floral resources for pollinators. At the local scale, we considered effects of (v) cherry flower density and (vi) heterospecific flower density. Pollinators visited flowers more often in landscapes with high amount of woody habitat and at sites with lower isolation from the next cherry tree. Fruit set was reduced by isolation from the next cherry tree and by a high local density of heterospecific flowers but did not directly depend on pollinator visitation. These results reveal the importance of considering the plant's need for conspecific pollen and its pollen competition with co-flowering species rather than focusing only on pollinators’ habitat requirements and flower visitation. It proved to be important to disentangle habitat isolation from habitat loss, local from landscape-scale effects, and direct effects of pollen availability on fruit set from indirect effects via pollinator visitation to understand the delivery of an agriculturally important ecosystem service.

ContextMany connectivity metrics have been used to measure the connectivity of a landscape and to evaluate the effects of land-use changes and potential mitigation measures. However, there are still gaps in our understanding of how to accurately quantify landscape connectivity.ObjectivesA number of metrics only measure between-patch connectivity, i.e. the connectivity between different habitat patches, which can produce misleading results. This paper demonstrates that the inclusion of within-patch connectivity is important for accurate results.MethodsThe behavior of two metrics is compared: the Connectance Index (CONNECT), which measures only between-patch connectivity, and the effective mesh size (meff), which includes both within-patch and between-patch connectivity. The connectivity values of both metrics were calculated on a set of simulated landscapes. Twenty cities were then added to these landscapes to calculate the resulting changes in connectivity.ResultsWe found that when using CONNECT counter-intuitive results occurred due to not including within-patch connectivity, such as scenarios where connectivity increased with increasing habitat loss and fragmentation. These counter-intuitive results were resolved when using meff. For example, landscapes with low habitat amount may be particularly sensitive to urban development, but this is not reflected by CONNECT.ConclusionsApplying misleading results from metrics like CONNECT can have detrimental effects on natural ecosystems, because reductions in within-patch connectivity by human activities are neglected. Therefore, this paper provides evidence for the crucial need to consider the balance between within-patch connectivity and between-patch connectivity when calculating the connectivity of landscapes.

ContextHabitat fragmentation per se (habitat subdivision independent of habitat loss) is a major driver of biodiversity change, potentially due to its impacts on climate. Habitat fragmentation may make landscapes hotter by increasing the amount of habitat edges, but can reduce landscape-level temperatures due to the “vegetation breeze” phenomenon. The plausibility of these two alternative hypotheses is unclear, as no study analyzed the effects of habitat fragmentation per se on temperature.ObjectivesWe quantify, for the first time, the impacts of habitat fragmentation on landscape-level temperature across the globe.MethodsWe analyzed satellite data on forest cover and three climatic variables: mean daily temperature, albedo and evapotranspiration. The analyses were performed separately for tropical, temperate, and boreal regions. We compared the climatic variables between pairs of landscapes with similar amount of forest, but different levels of forest fragmentation (number of patches).ResultsHabitat fragmentation reduced landscape-level temperature in all climatic regions. The magnitude of this cooling was stronger in the tropics and weaker in the boreal region due to different evapotranspiration rates. This landscape-scale cooling contradicts local-scale studies, which have indicated that edge effects rise local temperatures. However, habitat fragmentation may intensify vegetation breeze, resulting in final cooling at the landscape scale.ConclusionsHabitat fragmentation leads to colder landscapes. We propose a new conceptual model to unify local (edge-induced) and landscape-level effects of habitat fragmentation on temperature, advancing the understanding of the consequences of habitat fragmentation on climate globally.

Context Landscape habitat amount is known to increase biodiversity, while the effects of habitat fragmentation are still debated. It has been suggested that negative fragmentation effects may occur with a time lag, which could explain inconsistent results. However, there is so far no empirical support for this idea. Objectives We evaluated whether habitat amount and fragmentation at the landscape scale affect the species density of deadwood-dwelling lichens, and whether these effects occur with a time lag. Methods We surveyed deadwood-dwelling lichens in woodland key habitats in two regions in northern Sweden, and modelled their species density as a function of past (1960s) and present (2010s) habitat amount (old forest area) and fragmentation (edge density) in the surrounding landscapes. Results Present habitat amount generally had weak positive effects on lichen species density. Positive effects of the past habitat amount were stronger, indicating a time lag in habitat amount effects. Habitat fragmentation effects were generally weak and similar whether fragmentation was measured in the past or the present landscapes, indicating no time lag in fragmentation effects. Conclusions We found a time lag effect of habitat amount, but not fragmentation. This result is not consistent with suggestions that time lags explain the mixed observations of fragmentation effects. Time-lag effects of habitat amount suggest that the studied lichen communities face an extinction debt. Conservation should therefore prioritize increasing the amount of old forest, for example by creating forest reserves, to maintain the current lichen diversity. More generally, our results imply that studies examining only the present habitat amount risk under-estimating its importance.

ContextHabitat loss has clear negative effects on biodiversity, but whether fragmentation per se (FPS), excluding habitat loss does is debatable. A contribution to this debate may be that many fragmentation studies tend to use landscapes of fragmented focal-habitat and a single vastly different species-poor intervening land cover (the matrix).ObjectivesHow does matrix composition influence the effect of FPS on biodiversity?.MethodsUsing an individual-based model to investigate the effect of different configurations of the matrix on the relationship between FPS and biodiversity of the focal-habitat. We manipulated the number and quality of land cover types in the matrix, and their similarity to the focal-habitat.ResultsExtremely different matrix, caused an order of magnitude stronger effect of FPS on alpha- and gamma-diversity and beta-diversity to decline. Low FPS led to high gamma-diversity. Increasing FPS caused a dramatic decline to low diversity. In contrast landscapes with a more similar matrix had lower diversity under low FPS declining little with increasing FPS. Having few matrix types caused beta-diversity to decline in general compared to landscapes with a larger numbers.ConclusionsThe effects of FPS on biodiversity may change depending on the number of matrix types and their similarity to the focal-habitat. We recommend that fragmentation studies should consider a greater variety of landscapes to help assess in which cases FPS does not have a negative impact and allow better predictions of the impacts of fragmentation. We show the importance of having a diversity of matrix land cover types and improving the hospitability of the matrix for species dependent on the focal-habitat.

To determine whether we can reduce the impacts of forest loss on biodiversity by altering forest pattern, we need to estimate the effects of forest pattern independent of forest amount. We evaluated the independent and interactive effects of forest amount, fragmentation, and connectivity (wooded corridors) on diversity of forest‐associated plants, small mammals, and birds. We selected 70 forest sites in eastern Ontario, Canada with low correlations between these landscape predictors. We found positive effects of forest amount, neutral or positive effects of forest fragmentation, and an interaction effect between connectivity and forest amount. In landscapes with low forest amount, biodiversity increased with connectivity, while at high forest amount, biodiversity decreased with connectivity. Thus, forest patches should be protected regardless of size, and conservation actions aimed at improving connectivity by adding wooded corridors should be prioritized in areas where forest is scarce, for example agricultural and urban areas.

ContextHabitat loss is widely recognized as the main driver of biodiversity loss around the globe, yet the effects of habitat fragmentation on biodiversity have been extensively debated in recent years.ObjectivesWe used a robust dataset of medium and large-sized mammals to test (a) the Habitat Amount Hypothesis, which postulates that species richness can be mainly predicted by the total amount of habitat surrounding the sampling site, and (b) the effects of habitat fragmentation per se, which may be expected to be weak or mainly positive on species richness.MethodsWe compiled information on the occurrence of mammal species in 166 forest fragments across the Atlantic Forest. For each forest fragment, we extracted information on patch size, percentage of forest cover (a proxy for habitat amount), and edge density and number of fragments (fragmentation metrics). We related these metrics to mammalian richness considering separately for all species, forest-dependent species, disturbance-tolerant species, and different trophic guilds.ResultsAll richness measures strongly declined with decreasing forest cover, yet were unaffected by patch size, number of patches and edge density. The only exception occurred with herbivore richness, which was affected by number of patches. However, we found fragmentation per se effects only for herbivore richness.ConclusionsOur results show that mammal richness increased with habitat amount at the landscape, whereas habitat fragmentation per se had significant negative impacts on herbivores only. We therefore recommend maintaining highly forested landscapes and restoring severely deforested areas, being essential for ensuring high richness of mammals.