CiteULike: neteler connectivity

Using Landscape Indices to Predict Habitat Connectivity

NH Schumaker — 2006-01-26T10:54:04-00:00

Ecology, Vol. 77, No. 4. (1996), pp. 1210-1225.

The ecological consequences of habitat fragmentation include the direct effects of habitat loss and the indirect effects of reduced inter-patch dispersal. In particular, habitat patches that survive the process of fragmentation become increasingly isolated from one another, and this can cause species' declines in excess of predictions based strictly on reductions in habitat area. To quantify the hindrance of dispersal caused by habitat fragmentation, landscape ecologists have invented the notion of habitat connectivity. Indices of landscape pattern are frequently used to estimate habitat connectivity, but whether they actually do so remains undocumented. If indices of habitat pattern do indeed estimate habitat connectivity, then these indices should correlate well with predictions of dispersal success. To test this possibility, I looked for correlations between nine common indices of habitat pattern and the results of a simulated dispersal process conducted using GIS data on the distribution of old-growth forest through the Pacific Northwest. The nine indices of habitat pattern that I examined were only weakly correlated with the results from the dispersal modelling, but I identified a new pattern index, termed patch cohesion, for which the fit was much better. Moreover, I found patch cohesion to be insensitive to the details and artifacts of the dispersal model. The methodology described here will be useful to investigators using indices of landscape pattern to quantify habitat fragmentation.

Animal dispersal in fragmented habitat: measuring habitat connectivity, corridor use, and dispersal mortality

L Brooker — 2006-01-26T10:58:36-00:00

Conservation Ecology, Vol. 3, No. 4. (1999)

We used a spatially explicit dispersal simulation to generate movement frequencies and distances for comparison with real dispersal frequencies collected in the field from two habitat-specific, sedentary bird species. The relationship between these two data sets allowed us to (1) test the hypothesis that the study species used corridor routes during dispersal; (2) measure the degree of reliance on corridor continuity; (3) estimate the rate of dispersal mortality with respect to distance traveled, and (4) give examples of how the model can be used to assess habitat connectivity with respect to similarly behaved species. We found that Blue-breasted Fairy-wrens and White-browed Babblers both used corridor routes during dispersal. Blue-breasted Fairy-wrens were inhibited by gaps greater than about 60 m, whereas White-browed Babblers crossed gaps of at least 270 m wide. For each species, the rate of dispersal mortality per unit distance traveled was about the same. Because we have effectively partitioned the risk of dispersal mortality from the chance of outside dispersal, and because our mortality estimates are model dependent but landscape independent, they can be transported to other landscapes on which simulations have been run and, therefore, can be used in population viability assessment of unstudied or hypothetical animal populations.

Understanding the Relationships between Landscape Connectivity and Abundance of Ixodes ricinus Ticks

Agustin Estrada-Pena — 2005-07-24T20:58:03-00:00

Experimental and Applied Acarology, Vol. 28, No. 1 - 4. (March 2002), pp. 239-248.

The relationships between habitat topology, critical scales of connectivity and tick abundance Ixodes ricinus in a heterogeneous landscape in northern Spain

A Estrada-Pena — 2005-07-22T14:32:56-00:00

Ecography, Vol. 26, No. 5. (October 2003), pp. 661-671.

The habitat mosaic was used to quantify connectivity between patches of different tick density of the notorious tick species Ixodes ricinus in an attempt to determine the cause of variations in tick abundance among apparently homogeneous sites in northern Spain. The analysis revealed that patches with high tick abundance are “stepping-stone” territories that, when removed from the landscape, cause large changes in connectivity. Sites with medium tick abundance do not cause such a critical transition in connectivity. Patches with low tick abundance, but optimal abiotic conditions for survival, are located within the minimum cost corridors network joining the patches, while those sites where the tick has been intermittently collected are located at variable distances from this network. Sites where the tick is consistently absent, but where the habitat is predicted to be suitable (old, heterogeneous forests of Quercus spp.) for the tick, are very separated from this main network of connections. These results suggest that tick distribution in a zone is highly affected not only by abiotic variables (vegetation and weather) but also by host movements. Dispersal of the tick is a function of how the hosts perceive the habitat, and the habitat's permeability to host movement. Permanent tick populations seem to be supported by the existence of these critical, high density patches, located at significant places within the habitat network.