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1.
Individual movement is a key process affecting the distribution of animals in heterogeneous landscapes. For specialist species in patchy habitat, a central issue is how dispersal distances are related to landscape structure. We compared dispersal distances for cactus bugs (Chelinidea vittiger) on two naturally fragmented landscapes (≤ 4% suitable habitat) with different matrix structures (i.e., vegetation height of nonsuitable habitat between suitable patches). Using mark-release-recapture studies, we determined that most transfers between cactus patches occurred during the mating season. Dispersal distances were reduced by > 50% on the landscape that had reduced structural connectivity due to relatively high matrix structure and low patch density. An experiment with detailed movement pathways demonstrated that greater matrix structure decreased mean step lengths, reduced directionality, and thus decreased net displacement by > 60%. However, habitat edges between two matrix elements that differed substantially in resistance to movement were completely permeable. Therefore, the difference in distributions of dispersal distances between the two landscapes mainly reflected the average resistance of matrix habitat and not the level of matrix heterogeneity per se. Our study highlights the merits of combining estimates of dispersal distances with insights on mechanisms from detailed movement pathways, and emphasizes the difficulty of treating dispersal distances of species as fixed traits independent of landscape structure. 相似文献
2.
Effects of patch attributes, barriers, and distance between patches on the distribution of a rock-dwelling rodent (Lagidium viscacia) 总被引:1,自引:0,他引:1
We tested whether size of habitat patches and distance between patches are sufficient to predict the distribution of the mountain
vizcacha Lagidium viscacia a large, rock-dwelling rodent of the Patagonian steppe Argentina, or whether information on other patch and landscape characteristics
also is required. A logistic regression model including the distance between rock crevices and depth of crevices, distance
between a patch and the nearest occupied patch, and whether or not there was a river separating it from the nearest occupied
patch was a better predictor of patch occupancy by mountain vizcachas than was a model based only on patch size and distance
between patches. Our results indicate that a simple metapopulation analysis based on size of habitat patches and distance
between patches may not provide an accurate representation of regional population dynamics if patches vary in habitat quality
independently of patch size and features in the matrix alter connectivity.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Measuring edge effects in complex landscapes is often confounded by the presence of different kinds of natural and anthropogenic
edges, each of which may act differently on organisms inhabiting habitat patches. In such landscapes, proportions of different
habitats surrounding nests within patches often vary and may affect nesting success independently of distance to edges. We
developed methods to measure and study the effects of multiple edges and varying habitat composition around nests on the breeding
success of the Acadian flycatcher (Empidonax virescens), an understory, open-cup nesting songbird. The Kaskaskia River in Southwestern Illinois was our study area and consists
of wide (>1000-m) floodplain corridors embedded in an agricultural matrix with a variety of natural (wide rivers, backwater
swamps, and oxbow lakes) and anthropogenic (internal openings, and agricultural) habitats. We also measured vegetation structure
around each nest. Nest survival increased with increasing nest concealment, and probabilities of brood parasitism increased
with increasing distances from anthropogenic and natural water-related openings surrounding nests. The magnitude of these
effects was small, probably because the landscape is saturated with nest predators and brood parasites. These results illustrate
the importance of considering both larger landscape context and details of natural and anthropogenic disturbances when studying
the effects of habitat fragmentation on wildlife. 相似文献
4.
For weak flying insects feeding on two different host plants during their life cycle, such as gall-inducing aphids, patch
and matrix characteristics may play a critical role in patch occupancy and population size in occupied patches. The aims of
the present study were to define the basic patch size of Baizongia pistaciae (L) (Aphididae, Fordini), an aphid inducing galls on Pistacia palaestina Boiss (Anacardiaceae) using a genetic approach, and to estimate the impact of landscape structure and patch quality on patch
occupancy and gall density on occupied trees of this aphid and four other closely related species. Using 42 genetic markers
detected by RAPD-PCR in 117 clones of the galling aphid Baizongia pistaciae, we calculated Wright's F statistics and estimated the number of winged migrants between demes. We found that host trees at least 150 m apart supported
genetically differentiated demes of B. pistaciae, and formed distinct patches. Since the annual cycle of this aphid involves alternation between two different hosts, P. palaestina trees and Poaceae roots, patch – the smallest area that sustains a deme – is a relatively small area that must be composed
of at least a single P. palaestina tree and nearby secondary hosts. To assess the impact of landscape structure and patch quality on patch occupancy and gall
abundance in occupied patches, two field surveys of P. palaestina trees in natural Mediterranean maquis were performed. Among the five species of gall-inducing aphids found, B. pistaciae was the most abundant of those surveyed. Host trees were occupied more often in the ecotone, the transition zone between
Mediterranean closed maquis and open bata, than in the maquis. Mature and old trees were more often occupied than young ones,
and shrubs more often than tree-like plants. There was no difference in the proportion of occupied trees between isolated
host trees or those growing in groups. Species richness showed similar trends. We also found no significant differences in
gall abundance in occupied trees among tree quality categories, except that trees growing in the ecotone tended to carry more
galls than those growing in the maquis. In conclusion, the best patch of gall-inducing aphids seems to be a small area, composed
of an old shrub of P. palaestina standing in an open landscape with nearby secondary hosts, grass roots, available for colonization by winged migrants. 相似文献