Calopteryx Damselfly Dispersions Arising from Multiscale Responses to Landscape Structure

Wing morphology of a damselfly exhibits local variation in response to forest fragmentation

Environmental differences can lead to morphologically different subpopulations. The scale of the mosaic of morphologies should help shed light on the nature of the mechanisms at work. Previous work has shown that jewelwing damselflies have different wing sizes in different types of habitat. Our aim was to (1) describe the relationship between damselfly wing lengths and a gradient of forest fragmentation and (2) determine the spatial scale at which these morphological differences occur. We hypothesized that local adaptation would lead to differences in wing morphology over short distances. We herein test one of the several predictions that would need to be met to support this hypothesis: that wing morphology would show spatial autocorrelation at relatively short distances. We further predicted that the wing morphology would correlate to forest fragmentation. We collected jewelwing damselflies from across Indiana, USA, in habitats across a gradient of forest fragmentation. We examined the link between forest edge density and wing length using three biologically relevant landscape sizes. We then examined the distance to which wing length variation was autocorrelated using Moran's I. We found positive linear or unimodal relationships between wing length and edge density, in both males and females, at all three landscape scales. Spatial autocorrelation in wing length indicated that variation in wing length was autocorrelated at short distances, out to 1-5 km. Our findings uphold one of the predictions stemming from the hypothesis that adaptations to local environments-habitat fragmentation here-can occur at relatively fine spatial scales.

Habitat-specific movement and edge-mediated behavior of the saproxylic insect Odontotaenius disjunctus (Coleoptera: Passalidae)

The ability to disperse among patches is central to population dynamics in fragmented landscapes. Although saproxylic (=dead wood dependent) insects live in extremely fragmented forest ecosystems and comprise a significant proportion of the biodiversity therein, few studies have focused on dispersal of members in this group. We quantified the terrestrial movements of Odontotaenius disjunctus Illiger, a common saproxylic beetle in eastern North American forests. Movement behavior of individual beetles was measured in deciduous forest and two common matrix (=unsuitable) habitats (urban lawn and cattle pasture). Probability of emigrating from a forest fragment was assessed at the high-contrast boundary between forest and pasture. Seasonal, diurnal, and sex-biased patterns of O. disjunctus dispersal were determined from captures at drift fences encircling inhabited logs. Movement was 1.6 and 2.7 times faster and 1.1 and 1.5 times more linear in suitable habitat (forest) than in unsuitable matrix (lawn and pasture, respectively). Net displacement in the forest exceeded predictions of a correlated random walk, but net displacement in matrix habitats was less than expected. When confronted with a high-contrast boundary, O. disjunctus was 14 times more likely to move toward the forest than the pasture. The importance of temperature was indicated by its positive relationship with movement rate and increased diurnal and warm season dispersal activity. Reluctance to cross boundaries into open fields and slow movement within open fields suggest a low likelihood of terrestrial O. disjunctus movement among forest fragments.

Independent effects of fragmentation on forest songbirds: an organism-based approach

The degree to which spatial patterns influence the dynamics and distribution of populations is a central question in ecology. This question is even more pressing in the context of rapid habitat loss and fragmentation, which threaten global biodiversity. However, the relative influence of habitat loss and landscape fragmentation, the spatial patterning of remaining habitat, remains unclear. If landscape pattern affects population size, managers may be able to design landscapes that mitigate habitat loss. We present the results of a mensurative experiment designed to test four habitat loss vs. fragmentation hypotheses. Unlike previous studies, we measured landscape structure using quantitative, spatially explicit habitat distribution models previously developed for two species: Blackburnian Warbler (Dendroica fusca) and Ovenbird (Seiurus aurocapilla). We used a stratified sampling design that reduced the confounding of habitat amount and fragmentation variables. Occurrence and reoccurrence of both species were strongly influenced by characteristics at scales greater than the individual territory, indicating little support for the random-sample hypothesis. However, the type and spatial extent of landscape influence differed. Both occurrence and reoccurrence of Blackburnian Warblers were influenced by the amount of poor-quality matrix at 300- and 2000-m spatial extents. The occurrence and reoccurrence of Ovenbirds depended on a landscape pattern variable, patch size, but only in cases when patches were isolated. These results support the hypothesis that landscape pattern is important for some species only when the amount of suitable habitat is low. Although theoretical models have predicted such an interaction between landscape fragmentation and composition, to our knowledge this is the first study to report empirical evidence of such nonlinear fragmentation effects. Defining landscapes quantitatively from an organism-based perspective may increase power to detect fragmentation effects, particularly in forest mosaics where boundaries between patches and matrix are ambiguous. Our results indicate that manipulating landscape pattern may reduce negative impacts of habitat loss for Ovenbird, but not Blackburnian Warbler. We emphasize that most variance in the occurrence of both species was explained by local scale or landscape composition variables rather than variables reflecting landscape pattern.

Metapopulation theory for fragmented landscapes

We review recent developments in spatially realistic metapopulation theory, which leads to quantitative models of the dynamics of species inhabiting highly fragmented landscapes. Our emphasis is in stochastic patch occupancy models, which describe the presence or absence of the focal species in habitat patches. We discuss a number of ecologically important quantities that can be derived from the full stochastic models and their deterministic approximations, with a particular aim of characterizing the respective roles of the structure of the landscape and the properties of the species. These quantities include the threshold condition for persistence, the contributions that individual habitat patches make to metapopulation dynamics and persistence, the time to metapopulation extinction, and the effective size of a metapopulation living in a heterogeneous patch network.