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

   https://doi.org/10.1002/ecy.4037  

   Fletcher, Robert J.; Smith, Thomas A.; Kortessis, Nicholas; Bruna, Emilio M.; Holt, Robert D. (May 2023, Ecology)

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

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2. Habitat edges decrease plant reproductive output in fragmented landscapes

   https://doi.org/10.1111/1365-2745.14452  

   Hulting, Katherine A; Brudvig, Lars A; Damschen, Ellen I; Levey, Douglas J; Resasco, Julian; Tewksbury, Joshua J; Haddad, Nick M (March 2025, Journal of Ecology)

   Abstract Habitat loss is a major threat to biodiversity, but the effects of habitat fragmentation are less clear. Examining drivers of key demographic processes, such as reproduction, will clarify species‐level responses to fragmentation and broader effects on biodiversity. Yet, understanding how fragmentation affects demography has been challenging due to the many ways landscapes are altered by co‐occurring habitat loss and fragmentation, coupled with the rarity of experiments to disentangle these effects.In a large, replicated fragmentation experiment with open savanna habitats surrounded by pine plantation forests, we tested the effects of inter‐patch connectivity, patch edge‐to‐area ratio, and within‐patch distance from an edge on plant reproductive output. Using five experimentally planted species of restoration interest—three wind‐pollinated grass species and two insect‐pollinated forb species—we measured plant flowering, pollination rate, and seed production.All plant species were more likely to flower and produce more flowering structures farther from the forest edge. Connectivity and distance from an edge, however, had no effect on the pollination rate (regardless of pollination mode). Despite no influence of fragmentation on pollination, plant seed production increased farther from the edge for four of five species, driven by the increase in flower production.Synthesis. Altogether, we demonstrate that plant reproductive output (seed production) is decreased by habitat fragmentation through edge effects on flowering. Our work provides evidence that an important contributor to plant demography, reproductive output, is altered by edge effects in fragmented patches. These species‐level impacts of fragmentation may provide insight into the mechanisms of fragmentation effects on community‐level changes in biodiversity. 

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3. Modeling effects of matrix heterogeneity on population persistence at the patch-level

   https://doi.org/10.3934/mbe.2022638  

   Fonseka, Nalin; Goddard Ⅱ, Jerome; Henderson, Alketa; Nichols, Dustin; Shivaji, Ratnasingham (September 2022, Mathematical Biosciences and Engineering)

   Yang Kuang (Ed.)

   Habitat loss and fragmentation is the largest contributing factor to species extinction and declining biodiversity. Landscapes are becoming highly spatially heterogeneous with varying degrees of human modification. Much theoretical study of habitat fragmentation has historically focused on a simple theoretical landscape with patches of habitat surrounded by a spatially homogeneous hostile matrix. However, terrestrial habitat patches are often surrounded by complex mosaics of many different land cover types, which are rarely ecologically neutral or completely inhospitable environments. We employ an extension of a reaction diffusion model to explore effects of heterogeneity in the matrix immediately surrounding a patch in a one-dimensional theoretical landscape. Exact dynamics of a population exhibiting logistic growth, an unbiased random walk in the patch and matrix, habitat preference at the patch/matrix interface, and two functionally different matrix types for the one-dimensional landscape is obtained. These results show existence of a minimum patch size (MPS), below which population persistence is not possible. This MPS can be estimated via empirically derived estimates of patch intrinsic growth rate and diffusion rate, habitat preference, and matrix death and diffusion rates. We conclude that local matrix heterogeneity can greatly change model predictions, and argue that conservation strategies should not only consider patch size, configuration, and quality, but also quality and spatial structure of the surrounding matrix. 

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4. Deer Vigilance and Movement Behavior Are Affected by Edge Density and Connectivity

   https://doi.org/10.1111/eth.13574  

   Bartel, Savannah L; Hakkila, Leotie; Orrock, John L (May 2025, Ethology)

   ABSTRACT Animal behavior is an important component of individual, population, and community responses to anthropogenic habitat alteration. For example, antipredator behavior (e.g., vigilance) and animal movement behavior may both be important behavioral responses to the increased density of habitat edges and changes in patch connectivity that characterize highly modified habitats. Importantly, edge density and connectivity might interact, and this interaction is likely to mediate animal behavior: linear, edge‐rich landscape features often provide structural connectivity between patches, but the functional connectedness of patches for animal use could depend upon how edge density modifies animal vigilance and movement. Using remote cameras in large‐scale experimental landscapes that manipulate edge density (high‐ vs. low‐density edges) and patch connectivity (isolated or connected patches), we examined the effects of edge density and connectivity on the antipredator behavior and movement behavior of white‐tailed deer (Odocoileus virginianus). Deer vigilance was 1.38 times greater near high‐density edges compared to low‐density edges, regardless of whether patches were connected or isolated. Deer were also more likely to move parallel to connected high‐density edges than all other edge types, suggesting that connectivity promotes movement along high‐density edges. These results suggest that increases in edge density that accompany human fragmentation of existing habitats may give rise to large‐scale changes in the antipredator behavior of deer. These results also suggest that conservation strategies that simultaneously manipulate edge density and connectivity (i.e., habitat corridors) may have multiple effects on different aspects of deer behavior: linear habitat corridors were areas of high vigilance, but also areas where deer movement behavior implied increased movement along the habitat edge. 

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5. Fundamental principles of the effect of habitat fragmentation on species with different movement rates

   https://doi.org/10.1111/cobi.14424  

   Jacobs, Jamaal; Salmaniw, Yurij; Lam, King‐Yeung; Zhai, Lu; Wang, Hao; Zhang, Bo (December 2024, Conservation Biology)

   Abstract Habitat loss and fragmentation have independent impacts on biodiversity; thus, field studies are needed to distinguish their impacts. Moreover, species with different locomotion rates respond differently to fragmentation, complicating direct comparisons of the effects of habitat loss and fragmentation across differing taxa and landscapes. To overcome these challenges, we combined mechanistic mathematical modeling and laboratory experiments to compare how species with different locomotion rates were affected by low (∼80% intact) and high (∼30% intact) levels of habitat loss. In our laboratory experiment, we usedCaenorhabditis elegansstrains with different locomotion rates and subjected them to the different levels of habitat loss and fragmentation by placingEscherichia coli(C. elegansfood) over different proportions of the Petri dish. We developed a partial differential equation model that incorporated spatial and biological phenomena to predict the impacts of habitat arrangement on populations. Only species with low rates of locomotion declined significantly in abundance as fragmentation increased in areas with low (p = 0.0270) and high (p = 0.0243) levels of habitat loss. Despite that species with high locomotion rates changed little in abundance regardless of the spatial arrangement of resources, they had the lowest abundance and growth rates in all environments because the negative effect of fragmentation created a mismatch between the population distribution and the resource distribution. Our findings shed new light on incorporating the role of locomotion in determining the effects of habitat fragmentation. 

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