Absence Of Corridors Research Articles

Are corridors, fragment size and forest structure important for the conservation of leaf-litter lizards in a fragmented landscape?

To investigate the implications of forest fragmentation for conservation of leaf-litter lizards the importance of fragment size, corridors and forest structure was examined in 20 forest fragments and six localities within a continuous forest in the Atlantic Plateau of São Paulo state, Brazil. The fragments were 2–276 ha in area and had different degrees of connectivity depending on the presence or absence of corridors. Two species of lizards were dominant, Ecpleopus gaudichaudii and Enyalius perditus. Variation in forest structure among sites was important only in explaining the abundance of E. perditus. Regardless of variation in forest structure, lizard species composition, total lizard abundance, number of species and abundance of E. perditus were sensitive to fragmentation per se but not to fragment size or corridor linkage. The inhospitable matrix surrounding fragments is probably what determines the presence and abundance of E. perditus and the higher lizard richness in continuous forests. These conditions may have prevented lizard species from recolonizing the forest fragments. Our results emphasize that the conservation of this leaf-litter fauna depends on the maintenance of large tracts of continuous forests and not on the size of fragments or on the presence of forest connections. Strategies for conservation of leaf-litter lizards in such highly fragmented Atlantic Forest landscapes should consider the enlargement of landscape connectivity between fragments and continuous forest, allowing the latter areas to act as a source of individuals for fragments.

Effect of corridors on the movement behavior of the jumping spider Phidippus princeps (Araneae, Salticidae)

Corridors are a common conservation strategy intended to increase the spatial connectivity among isolated habitat patches. Corridors, however, are not always effective. This study demonstrates that corridors increase movement to new patches for the jumping spider Phidippus princeps (Peckham and Peckham, 1883) (Araneae, Salticidae), a visually oriented predator. I assigned spiders to one of three microlandscape treatments, created in an old field dominated by alsike clover ( Trifolium hybridum L.) and alfalfa ( Medicago sativa L.), in which patches were connected to (i) vegetated corridors and bare pathways, (ii) only vegetated corridors, and (iii) only bare pathways. The movement of P. princeps was effectively directed by corridors. When given a choice of paths, spiders invariably chose vegetated corridors over bare pathways to emigrate from and to immigrate to new patches. Spiders rarely moved between patches when only bare pathways were available. In the absence of corridors, P. princeps did not risk open ground to move to new habitat even though conspecific density was high. The corridors facilitated the interpatch movement of P. princeps, suggesting that P. princeps is restricted in its habitat use. Thus, a higher degree of spatial connectivity is likely to increase the exchange of individuals for species that are restricted in their movements by unsuitable habitat.

Colonisation of newly established habitats by soil decomposer organisms: the effect of habitat corridors in relation to colonisation distance and habitat size

The aim of the present 2.5-year-long field experiment was to explore the ability of various members of the detrital food web to colonise newly established habitat patches in field conditions, either in the presence or absence of habitat corridors. Patch size and distance to the “mainland” (colonisation source) were manipulated to explore the scale dependency of the corridor effects. Sterilised humus patches, embedded in mineral soil regarded as uninhabitable (or non-preferred) matrix for the soil organisms, functioned as newly established habitats. Intact forest soil served as the source of colonisers. Three kinds of patches were established: large ones situated at relatively long distance from the colonisation source, and small ones situated either at long or short distance from the source. Corridors, when present, connected the patches to the intact forest soil. The presence of corridors consistently increased the species richness of soil fungi in the patches. Also bacterial species richness, number of microarthropod taxa and abundance of enchytraeid worms were sometimes increased by the presence of corridors. The response of bacterial species was assumed to be indirect, caused by the response of enchytraeid worms functioning as dispersal agents for the bacteria. Colonisation of the patches by soil organisms was virtually independent of patch size and colonisation distance, both in the presence and absence of corridors. This can be related to the resource-poor or otherwise sub-optimal conditions in the initially sterile humus soil, restricting the number of species able to establish themselves in the patches and/or utilise the corridors. Nevertheless, the results indicate that habitat corridors can facilitate the colonisation of unpopulated habitats by organisms with greatly different life history traits.

Landscape structure, habitat fragmentation, and the ecology of insects

Landscape structure, habitat fragmentation, and the ecology of insects

Corridor Length and Patch Colonization by a Butterfly, Junonia coenia

Abstract: Corridors have been proposed to reduce isolation and increase population persistence in fragmented landscapes, yet little research has evaluated the types of landscapes in which corridors will be most effective. I tested the hypothesis that corridors increase patch colonization by a butterfly, Junonia coenia, regardless of the butterfly's initial distance from a patch. I chose J. coenia because it has been shown to move between patches preferentially through corridors. Individuals were released 16–192 m away from open experimental patches into adjacent open corridors or forest. Neither corridors nor distance had a significant effect on patch colonization, but there was a significant interaction between the presence or absence of corridors and distance. At small distances (16–64 m), J. coenia was more likely to colonize open patches when released within forest than within open corridors, most likely because J. coenia used corridors as habitat. Nevertheless, patch colonization by butterflies released within forest decreased rapidly as distance from patches increased, as predicted by a null model of random movement. Colonization did not change with distance in the corridor, and at long distances (128–192 m), butterflies released in corridors were twice as likely to colonize open patches as those released in forest. These results suggest that one critical factor, interpatch distance, may determine the relative effectiveness of corridors and other landscape configurations, such as stepping stones, in reducing isolation in fragmented landscapes. When distances between patches are short compared to an animal's movement ability, a stepping stone approach may most effectively promote dispersal. Alternatively, the conservation value of corridors is highest relative to other habitat configurations when longer distances separate patches in fragmented landscapes.

Effects of experimental habitat fragmentation and connectivity on root vole demography

Summary 1. We used a factorial experimental design to test whether habitat fragmentation (two different fragment sizes) and connectivity (presence and absence of corridors between small fragments) affected population growth rate and two conventional measures of the demographic structure (proportion of reproductive adults and sex ratio) in 12 enclosed populations of root voles. 2. Because the matriline has been suggested to be a functional entity affecting the demography of Microtus populations, we employed a study protocol (including laboratory‐raised founder animals and intensive live trapping combined with fluorescent powder techniques), which enabled us to track the matrilineal genealogy in the populations. Thus, the effect of habitat structure on the matrilineal structure of the populations, quantified by the Shannon–Wiener diversity index, could be tested for the first time. 3. Population growth rate was density dependent, but neither this population parameter nor sex ratio and proportion of reproductive adults differed between the habitat treatments. This was unexpected since the presumed determinants of Microtus demography, such as individual space use, dispersal distances and spatio‐social organization had earlier been found to differ between the treatments. 4. The matrilineal structure (diversity) of the populations changed in response to the experimental habitat manipulations. In corridor‐connected systems, some matrilines became numerically dominant, which lead to reduced matrilineal diversity compared to systems with isolated habitat fragments. We hypothesize that some matrilines were able to colonize and exploit corridor‐connected fragments better than other matrilines. Matrilineal diversity was not related to any other demographic attribute (growth rate, sex ratio and functional stage structure) at the population level. 5. Our results suggest that fragmentation‐induced changes of individual and matrilineal level attributes do not necessarily propagate into population level differences in vital rates. The notion that matrilines may be a functional entity in Microtus populations could not be supported. 6. Our experimental results suggest that population genetics, more than population demography, may be sensitive to habitat fragmentation and connectivity, within the specific temporal and spatial extent explored. In particular, the effect of corridors on matrilineal diversity imply that population genetic studies based on mtDNA markers should consider habitat connectivity when analysing genetic diversity.