conservation.arizona.edu - habitat fragmentation

Koprowski, J. L. 2005. The response of tree squirrels to fragmentation: A review and synthesis. Animal Conservation 8: 369-376.

thackerk1 — Mon, 22 Jul 2019 23:29:48 +0000

Authors

John L. Koprowski

Habitat fragmentation is often considered a major threat to biodiversity; however, our understanding of how fragmentation impacts populations is poor. Identifying appropriate models for such studies is difficult. Tree squirrels are dependent on mature forests for food, cover and nests; these are habitats that are being fragmented rapidly and that are easily defined by humans. Squirrels represent excellent models for study of fragmentation. The literature on tree squirrels was reviewed to glean data on density and home-range size in forest fragments. Sufficient data were available on four species (Sciurus carolinensis, S. niger, S. vulgaris, Tamiasciurus hudsonicus). Density was negatively related to fragment size for S. carolinensis and S. niger and marginally so for T. hudsonicus. Sciurus vulgaris did not exhibit this relationship. Home-range size was analyzed for three species of Sciurus and was positively related to forest fragment size for S. carolinensis and S. niger. Again, only S. vulgaris did not to show this relationship. Sciurus vulgaris is rarely found in small forest fragments and is believed to be especially sensitive to fragmentation; other tree squirrels appear to be sensitive to fragmentation in more subtle ways. Home range compaction provides a mechanism by which densities may increase in small fragments. The demographic consequences resultant from the high densities of squirrels found in small woodlots are not known but may explain the forest damage, avian nest predation and reduced diversity often cited to occur in woodland fragments.

Additional Information

The response of tree squirrels to fragmentation: a review and synthesis

Date of publication:

2005

Topics

habitat fragmentation

biodiversity

tree squirrels

home range

density

Chen, H. L. and J. L. Koprowski. 2015. Animal occurrence and space use change in the landscape of anthropogenic noise. Biological Conservation 192:315-322.

thackerk1 — Thu, 20 Jun 2019 23:12:02 +0000

Authors

Hsiang Ling Chen

John L. Koprowski

Habitat fragmentation, destruction, and disturbance are major threats to biodiversity. Global road networks represent one of the most significant human impacts on ecosystems, and a spatially extensive source of anthropogenic disturbance and noise. We developed a novel approach by combining traffic monitoring with noise mapping on the basis of a standardized traffic-noise stimulus generated by controlled vehicle operation to investigate temporal and spatial heterogeneity of traffic noise. We used animal presence or absence, radio-telemetric monitoring of space use, and remotely sensed habitat characteristics with occupancy modeling and spatial analysis to assess influences of distance from roads, habitat characteristics, and traffic noise level on site occupancy and space use of Mt. Graham red squirrels (Tamiasciurus hudsonicus grahamensis). Traffic noise had spatially ex- tensive and negative effects on site occupancy. Animal occurrence decreased as traffic noise increased after accounting for distance from roads. Traffic noise levels in animal core home ranges were lower than noise levels within total home ranges. Our study disentangled effects of traffic noise from confounding environmental characteristics and demonstrated the chronic impacts of traffic noise on animal distribution. We highlight the importance of incorporating spatial and temporal heterogeneity of traffic noise at a local scale when investigating effects of anthropogenic noise on wildlife.

Additional Information

Animal occurrence and space use change in the landscape of anthropogenic noise

Date of publication:

2015

Topics

habitat fragmentation

forest roads

site occupancy

road ecology

traffic noise

Mount Graham Red Squirrel

Barrier effects of roads on an endangered forest obligate: influences of traffic, road edges, and gaps

thackerk1 — Thu, 20 Jun 2019 22:59:51 +0000

Authors

Hsiang Ling Chen

John L. Koprowski

Habitat fragmentation and destruction caused by development of infrastructure such as roads threaten biodiversity. Roads act as barriers by impeding animal movements and restricting space use. Understanding factors that influence barrier effects is important to discern the impacts of habitat fragmentation and to develop appropriate mitigations. We combined telemetry and demographic data in 2008 to 2012 with remote sensing imagery to investigate barrier effects of forest roads and assess effects of traffic, road edges, and canopy gaps on space use of an endangered, endemic forest obligate, the Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis). We mapped low to high traffic roads, road edges, canopy gaps, and random lines in forests to serve as references. We determined if red squirrels included these linear features in their total and core home ranges, and used this metric as an indicator of crossing and preference for habitat adjacent to the linear features. Forest roads acted as barriers regardless of traffic volume and had long-term impacts on animal space use. Animals did not avoid entering roadside areas, and probability of crossing linear features in the forest was not affected by distance to roads. In contrast, greater canopy cover increased probability of crossing, and gaps in canopy impeded animal movements. Higher likelihood of road crossing was associated with more variable tree height and mating activity. We demonstrated that narrow forest roads with low traffic volume were barriers for forest dependent species, and suggest that gap avoidance inhibits road crossings.

Additional Information

Biological Conservation 199:33-40.

Date of publication:

2016

Topics

habitat fragmentation

gap avoidance

forest roads

forest structure

small mammals

road impacts

Research Categories

Behavioral Ecology Disturbance Ecology Sky Islands Threatened and Endangered Species