Gray Merriam

Habitat Patch Connectivity and Population Survival

We constructed a patch dynamics model which can be used to simulate the changing sizes of resident populations in a series of interconnected habitat patches. We applied the model to white—footed mice (Peromyscus Leucopus) inhabiting patches of forest in an agricultural landscape. The model predicts that mouse populations in isolated woodlots have lower growth rates and are thus more prone to extinction than those in connected woodlots. Field data support this prediction.

Mosaic Landscapes and Ecological Processes

Landscape mosaics and ecological theory. Origin of landscape pattern. Response of individuals and populations to landscape pattern. Landscape pattern, population dynamics and population genetics. Effects of landscape pattern on species interations. Implications for conservation. Summary: Ecology of mosaic landscapes: Consolidation, extension and application. Index.

INDEPENDENT EFFECTS OF FOREST COVER AND FRAGMENTATION ON THE DISTRIBUTION OF FOREST BREEDING BIRDS

The aims of this study were (1) to determine the relative importance of the independent effects of forest cover and fragmentation on the distribution of forest breeding birds, and (2) to test the hypothesis that the negative effect of forest fragmentation on species distribution increases with decreasing forest cover, i.e., the negative interaction effect of forest cover and fragmentation on distribution. The independent effects of forest cover and forest fragmentation on the distribution of forest breeding birds were studied in 94 landscapes, 10 × 10 km each, ranging in forest cover from 2.5% to 55.8%. For each landscape, percent forest cover was measured, and a fragmentation index (independent of forest cover) was generated using PCA from the measures of mean forest patch size, number of forest patches, and total forest edge. Presence of 31 forest breeding bird species in each landscape was determined using Breeding Bird Atlas data. The effects of forest cover and forest fragmentation on species presenc...

Movements by Birds and Small Mammals Between a Wood and Adjoining Farmland Habitats

(1) White-footed mice (Peromyscus leucopus) and chipmunks (Tamias striatus) moved between a beech-maple wood and connecting fencerows four times as often as they moved between traplines within the wood. They seldom moved between the wood and adjacent perennial grass fields or across the fields. (2) Birds seldom flew directly across open fields between woods. More species of birds moved more frequently between the wood and fencerows than between any other habitats. Wood-nesting birds moved more frequently from well-vegetated fencerows into fields to forage than from an equal length of wood border. Poorly developed fencerow vegetation restricted foraging by wood-nesters into fields. None of tree species diversity, line intercept measures, dendrograms, or foliage height diversity satisfactorily distinguished among the vegetation structure of different fencerows. (3) The results indicate that fencerows connect the wood to the surrounding agricultural mosaic and concentrate the activity of small mammals and birds into a habitat corridor that may relieve the isolating effect of farmland surrounding the wood.

Patchy environments and species survival: Chipmunks in an agricultural mosaic

Abstract Chipmunks were studied in woods separated by farmland and connected by fencerows. Local extinctions of chipmunks from individual woods were readily recolonised by animals from other patches. Fencerows formed critical connections among woods. A minimum area for considering population survival includes several woods and interconnecting fencerows. Such landscape mosaics should be the elementary units in much conservation planning and management.

The elements of connectivity where corridor quality is variable

AbstractSmall mammals in heterogeneous environments have been found to disperse along corridors connecting habitat patches. Corridors may have different survivability values depending on their size and the degree of cover they provide.This deterministic model tests the effects of varying corridor quality on the demographics of a metapopulation of Peromyscus leucopus. Two types of corridors are defined based on the probability of survival during a dispersal event.Results indicate that mortality during movement through corridors influences metapopulation demographics. We found that:1.Any connection between two isolated patches is better than no connection at all in terms of persistence and population size at equilibrium.2.Metapopulations with exclusively high quality corridors between patches have a larger population size at equilibrium than do those with one or more low quality corridors.3.Increasing the number of high quality corridors between patches has a positive effect on the size of the metapopulation while increasing the number of low quality corridors has a negative effect.4.The addition to a metapopulation of a patch connected by low quality corridors has a negative effect on the metapopulation size. This suggest the need for caution in planning corridors in a managed landscape.5.There is no relationship between the number of corridors and the metapopulation size at equilibrium when the number of connected patches is held constant.6.Geometrically isolated patches connected by low quality corridors are most vulnerable to local extinctions. We conclude that corridor quality is an important element of connectivity. It contributes substantially to the effects of fragmentation and should be carefully considered by landscape planners.

Barriers as boundaries for metapopulations and demes of Peromyscus leucopus in farm landscapes

Effects of potential barriers (roads and cultivated fields) on both demographic and genetic features of subpopulations of white-footed mice were studied near Ottawa, Canada. Live trapping, colored bait and track registry were used to study animal movements across roads on four 1.44 ha areas each within a small forest bisected by a narrow gravel road. The genetic study was done in 11 other forest fragments separated from each other by cultivated fields. Frequencies of three electrophoretic variants of salivary amylases were established for mice caught in each patch of wood and genetic similarity of subpopulations was calculated. Movements of mice across the roads were very infrequent (quantitative barrier), although movements adjacent to roads were frequent and long enough to cross the roads. Salivary amylase data showed that studied subpopulations were genetically very similar although the sample was intentionally biased toward demographic isolation. Results are discussed in terms of possible hierarchical relationships of metapopulations and genetic demes in the context of landscape ecology, management and conservation practice.

Corridor use by small mammals: field measurement for three experimental types of Peromyscus leucopus

Eighteen mice of each of 3 types were radio-tagged and released at 6 standard points in farmland fencerows. Mice were residents (trapped on site) or translocated from distant forest or from distant corn fields. Of total (net) distance moved, most was in fencerows; 77% for residents, 83% for mice translocated from cropland and 92% for mice translocated from forest. Structurally complex fencerows were preferred significantly over intermediate or simple structures by all types of mice. Time spent in movement was not a linear function of distance moved and averaged from 12.5 to 16.5% of total available activity time. Total distance moved in 2 nights averaged 287 to 422 m and area explored averaged 0.67 to 1.15 ha and ranged to 11.0 ha; both exceed literature values for this species in forest. This enlarged scale of landscape use illustrates the potential importance of landscape-specific behaviour. The measurement of rate of corridor use also is discussed.

Corridor use and the elements of corridor quality: Chipmunks and fencerows in a farmland mosaic

Abstract An important issue in developing practical conservation actions and in understanding how corridors function is that of identifying what constitutes a high quality corridor for a particular species or assemblage. We studied the use of fencerow corridors by the eastern chipmunk Tamias striatus to identify the elements of corridor quality for an animal species. Chipmunks were trapped in four woods and 18 fencerows of varying width, habitat and linear continuity, in farmland near Ottawa, Canada. There were many recorded movements by individuals within and between fencerows and woods. Chipmunks used fencerows in at least two main ways, and the elements of corridor quality were found to differ for these two modes of use. Resident individuals lived within and along many fencerows, thus promoting continuity of the resident population between woods. They favoured fencerows with tall trees and a woodland structure; neither fencerow width nor linear continuity accounted for additional variation in the number of residents after habitat attributes were included in a stepwise regression model. Transient chipmunks, those trapped once only in a fencerow, apparently used the fencerow network as a pathway through farmland. Linear continuity of fencerows was the most important correlate of the number of transients, with habitat attributes explaining additional variance in a regression model. Fencerows with grassy vegetation alone were never used by chipmunks and, like the surrounding farmland, appear to be inhospitable habitat. The different ways that individuals may use corridors, and the differing elements of corridor quality, have implications for models of corridor use and metapopulation function, and for practical corridor management and restoration.

Wing Morphology of a Forest Damselfly Is Related to Landscape Structure

We demonstrate that, after correcting for the effects of size, the wing lengths, wing widths and thoracic weights of the forest damselfly Calopteryx maculata differ between populations along forested streams, and those along streams through pasture. Pasture landscapes can be considered as fragmented forest landscapes; forest landscapes are continuous. In the fragmented landscapes some C. maculata fly across intervening pasture to reach foraging sites in forest. We propose that there is morphological plasticity within the species that is revealed through the landscape process of habitat fragmentation and that there is micro-scale selection within the fragmented landscapes for individuals that are better suited to make these flights