John Wegner

EFFECT OF ROAD TRAFFIC ON AMPHIBIAN DENSITY

We studied the effect of traffic intensity on local abundance of anurans. We counted dead and live frogs and toads per km and estimated frog and toad local abundances using breeding chorus intensities on similar roads through similar habitats, but with different levels of traffic intensity. After correcting for effects of date, local habitat, time, and region, our analyses demonstrated that (1) the number of dead and live frogs and toads per km decreased with increasing traffic intensity; (2) the proportion of frogs and toads dead increased with increasing traffic intensity; and (3) the frog and toad density, as measured by the chorus intensity, decreased with increasing traffic intensity. Taken together, our results indicate that traffic mortality has a significant negative effect on the local density of anurans. Our results suggest that recent increases in traffic volumes worldwide are probably contributing to declines in amphibian populations, particularly in populated areas.

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.

Population effects of landscape model manipulation on two behaviourally different woodland small mammals

We designed an individual-based simulation model to explore the effects of landscape spatial structure and connectivity on the population size and persistence of two woodland small mammal species, eastern chipmunks (Tamias striatus) and white-footed mice (Peromyscus leucopus), occurring in an agricultural landscape and occupying different positions on a gradient of behavioural flexibility in response to landscape change. Chipmunks represent a less flexible response, retaining their preference for wooded habitat. White-footed mice represent a more flexible, opportunistic response, expanding their use of the landscape to include corn and small-grain fields. Model parameters were derived from out field studies. The simulations followed chipmunk populations over 25 yr in 36 landscape patterns, each with a unique combination of amount of wooded habitat (10%, 30%, or 50% of the total area), subdivision of wooded habitat (2, 4, or 8 patches), and quality of connectivity (high, intermediate, low, or none). Mouse populations were simulated in 8 of these landscapes (30%, wooded habitat, 4 patches at each level of connectivity, and 10% wooded habitat, 8 patches at each level of connectivity). Generalist mice outperformed specialist chipmunks in all subdivided landscapes in which they were compared. Since generalist mice were not restricted to woods and fencerows, all landscapes were highly connected for them and provided over 75% usable habitat. Survival rates for these mice were high in all landscape patterns. For opportunistic species able to use novel resources, landscape change may not be limiting. Connectivity was the best predictor of population persistence for specialist species that view the matrix as hostile. Chipmunk population survival was always greater in connected landscapes than in unconnected ones. Interactions of connectivity, composition and configuration were also important. Long survival times and low probabilities of extinction for chipmunk populations occurred in model landscapes with 30% or more woodland, and high and intermediate quality connectivity. Chipmunk populations in 8 patch landscapes with only 10% woodland and low connectivity had high extinction probabilities. Highly variable population size increased risk of extinction, especially when amount of wooded habitat was low. For behaviourally inflexible species, maintenance of habitat connectivity when habitat subdivision and accompanying habitat loss occur is vital to survival.

Use of spatial elements in a farmland mosaic by a Woodland Rodent

Abstract We studied the use of agricultural landscapes in eastern Ontario, Canada, by white-footed mice Peromyscus leucopus. P. leucopus was common in all patch types except hay and pasture. Densities were similar in woods and in corn Zea mays (maize) fields. Temporal changes in numbers also were similar in crops and woods with low numbers in spring rising to a peak in early autumn. Some mice remained in ploughed corn fields all winter. Monthly turnover of individuals was 75% in areas up to 13·5 ha. Agricultural intensity had little effect on numbers of mice, but did influence the relative use of fencerows by P. leucopus. On low-intensity farms many more mice were captured in fencerows than in crop fields. P. leucopus has adapted to agricultural fields in the landscape mosaic of eastern Ontario.

Local Extinctions, Habitat Fragmentation, and Ecotones

In this chapter, extinctions are explored in the context of mechanisms that operate during and after habitat fragmentation of, and with frequent references to, woodlands in farmland, where we have studied the process, although information from many other situations are also used. An ecotone that is relevant to a particular species must be a gradient from more survivable to less survivable conditions. A high density of these circumstances should be conducive to observing the processes of local extinction. Fragmentation creates ecotones, expands them, and moves them. Therefore, from the information that we have about fragmentation effects, it may be possible to learn about the effects of changing ecotones on species extinctions.

Effects of Vegetation Type and Adjacent Agricultural Matrix on Fencerow Use by Small Mammals: A Nonmanipulative Experiment

The increasing scale of agricultural activity over the past several decades has resulted in the destruction of thousands of kilometres of semi-natural strips of wooded vegetation, termed fencerows, bordering crop fields. This loss is of concern because fencerows provide habitat for many organisms that might otherwise not be found in agricultural areas, including various plants (Baudry 1988, Marshall 1988, Bunce and Hallam 1993, Fritz and Merriam 1993, 1994, Jobin et al. 1996), insects (Burel 1989), birds (Wegner and Merriam 1979, Arnold 1983, Osborne 1984, Shalaway 1985, Green et al. 1994, Parrish et al. 1994, 1995, MacDonald and Johnson 1995, Sparks et al. 1996), and mammals (Ogilvie and Furman 1959, Pollard and Relton 1970, Eldridge 1972, Wegner and Merriam 1979, Middleton and Merriam 1981, Yahner 1983, Henderson et al. 1985, Bennett et al. 1994, Henein et al. 1998). Although less thoroughly demonstrated, wooded corridors or fencerows are also thought to provide dispersal routes for organisms moving between patches of remnant forest, thus contributing to the recolonization and/or rescue of local populations (Wegner and Merriam 1979, Fahrig and Merriam 1985, Johnson and Adkinsson 1985, Merriam and Lanoue 1990, Bennett et al. 1994).