Marina Silva

Differences in population density and energy use between birds and mammals : a macroecological perspective

1. Data from 364 mammal and 564 bird species were used to compare these two taxa in the patterns of variation in population density and energy use as a function of body mass. 2. This study demonstrates previously unappreciated quantitative differences between mammals and birds. Over a wide range of sizes, population densities and rates of energy use are at least one order of magnitude higher in mammals than in birds of similar size. The highest population densities are found in species that weigh about 100 g in mammals and 30 g in birds. 3. Comparisons between mammals and birds from the same dietary category indicate that mammals maintain higher densities and use more energy than birds. Insectivorous mammals and birds maintain the lowest densities. 4. Flying mammals and birds reach lower densities and use more energy than non-flying forms. 5. These findings reveal relationships between the morphology, physiology and behaviour of individual organisms and the ecological performance of these endothermic vertebrates in populations, communities and ecosystems: relationships that have not previously been appreciated.

Allometric Scaling of Body Length: Elastic or Geometric Similarity in Mammalian Design

Allometric scaling of body length was examined for 1,733 estimates of body length for a broad taxonomic and size range of mammals. Mammal species were classified by locomotion, habitat, and taxonomic relatedness. Scaling exponents found in different groups of mammals were compared to those predicted by geometric (0.333) and elastic (0.250) similitude models. The scaling exponent for the length : mass relationship 0.359 agreed better with the geometric-similitude model. However, the relationship between body length and body mass was not linear as previously postulated, and differences in the scaling exponent were found between marine and terrestrial mammals and between volant and non-volant forms. Allometric scaling of body length also varied among orders and families of mammals.

Habitat use and home range size of red foxes in Prince Edward Island (Canada) based on snow-tracking and radio-telemetry data

There is a lack of information regarding the ecology and behaviour of red foxes that can be used to elaborate effective management programs for this species on Prince Edward Island (Canada). The main goal of this study was to provide baseline information on habitat selection and home range size of red foxes on Prince Edward Island. Data were collected from snow-tracking and radio-telemetry sessions conducted in two study sites (including one site within Prince Edward Island National Park). Our results indicated that red foxes selected for roads and human-use areas during both the breeding and the kit-rearing seasons in the park. Outside the park, however, the data failed to conclusively show that foxes have a unique preference for human-use habitats or roads. Forests were selected against in both study sites. Although roads are frequently visited by foxes during the kit-rearing season in the park, each individual fox typically stays in this habitat only for short periods of time (< 15 min). This finding suggests that foraging efficiency along the roads is very high possibly reflecting the abundance of anthropogenic food sources. Overall, we present the largest amount of data on habitat selection ever collected for red foxes in Prince Edward Island, Canada. Our results show that food sources in human-use areas and roads are altering the selection and/or use of habitats of red foxes in some areas of Prince Edward Island.

The Conservation Value of Hedgerows for Small Mammals in Prince Edward Island, Canada

ABSTRACT The aim of this study was to investigate the use of hedgerows by small mammals in four agricultural landscapes in Prince Edward Island, Canada. The Island has one of the highest percentages of land (about 48%) devoted to crop production and pasture in all of Canada. Therefore, identifying the landscape elements that can mitigate the effects of habitat fragmentation resulting from agricultural practices is essential to preserve the biodiversity of Prince Edward Island. We quantified species richness, abundance and diversity of small mammals in 13 hedgerows and 13 attached forest patches. Although all the species detected in forest patches were also found in hedgerows, significant differences in species diversity and abundance suggest that not all species benefit equally from hedgerows. The abundance of small mammals other than the eastern chipmunk (Tamias striatus) increased in hedgerows longer than about 225–250 m, but was independent of hedgerows length in hedgerows smaller than 225–250 m. Predators (Mustela erminea) were captured in hedgerows, but not in forest patches. Relationships between small mammal variables and hedgerow features (microhabitat, macrohabitat and landscape) suggested that most small mammal species would benefit from hedgerows having high shrub diversity, ground cover with vines and leaf litter, and few non-vegetated gaps. Removal of hedgerows, especially large ones, may affect long-term survival of some small mammal species inhabiting agricultural landscapes of Prince Edward Island.

Abundance and Species Richness of Shrews within Forested Habitats on Prince Edward Island

Abstract Little is known about the small mammalian fauna of Prince Edward Island, particularly shrews. Although historical data indicate the presence of five shrew species on PEI (Sorex cinereus, S. fumeus, S. hoyi, S. palustris and Blarina brevicauda), recent studies have failed to capture S. fumeus, S. hoyi and S. palustris on the Island. During a study designed to examine the abundance of amphibians in 11 forest fragments located in the central region of Prince Edward Island, we collected 344 shrews in pitfall traps. Sorex cinereus was the most abundant species captured, and was present in all forest fragments. Blarina brevicauda was captured in all but one forest fragment. Sorex fumeus was found in only one fragment. Sorex hoyi and S. palustris were not captured during this study. No significant correlations were found between physical characteristics of forest remnants (i.e., area, perimeter, ratio area:perimeter) and the total abundance, species richness or species diversity of shrews. However, shrew captures were correlated with various biotic characteristics including ground temperature, the presence of canopy cover, number of stumps and number of logs. We conclude that both B. brevicauda and S. cinereus are common and widespread-distributed on Prince Edward Island. In conjunction with other recent studies, our findings indicate that S. hoyi is extremely rare on the Island and that it is possible that the species is extirpated from Prince Edward Island. We stress the need for a more comprehensive study specifically designed to determine the abundance, distribution and conservation status of shrew species on Prince Edward Island.