The picture to the right is an aerial photograph of Fermi National Accelerator Laboratory illustrating the heterogeneous landscape. Seven different habitats were sampled for two years to compare prey availability across the landscape. A log-linear analysis was then used to relate spatio-temporal changes in prey to the diets and activity patterns of the predators. The results showed that the numerically common predators, red fox, coyote, Red-tailed Hawk, and Great Horned Owl, feed heavily on rabbits and voles. Squirrels and field mice suffer comparatively low predation rates.
We then examined how predation affects the biology of small prairie mammals, such as mice and voles, by excluding the predators. There were four plots, each 1.5 acres in area, that had the coyotes and red foxes fenced out. Hawks and owls were excluded by suspending netting above the plots. Small mammals on the four exclusion plots and four control plots were trapped at monthly intervals to monitor long-term demographic patterns. The two most common small mammals occurring at the site were white-footed mice (Peromyscus leucopus) and meadow voles (Microtus pennsylvanicus). Following peak densities in late summer, Microtus numbers were as much as three times greater on exclusion plots relative to controls. This was due to preferential selection of Microtus by vertebrate predators, as reflected in their diets. Vertebrate predator exclusion had no detectable effect on Peromyscus numbers; this may have been attributed to an abundance of alternative prey, particularly eastern cottontails.
We also burned and mowed a portion of the field site. This was intended to test how predators affect prey populations, how different prairie management techniques affect prey populations, and how these different trophic levels ultimately interact in a tallgrass prairie restoration. Plant sampling involved the use of 60, 0.5-m quadrats distributed between mowed, burned, and control plots in the summer through fall months. Vegetation profiles were also taken to measure litter depth and vegetation structure. Plant data will be coupled with the small mammal censuses to look at how different prairie restoration techniques determine the species composition and abundance of plants and, in turn, vertebrate prey within the tallgrass prairie ecosystem.
The predator exclosures were also used to examine the effects of reduced predation risk on the foraging behavior of Peromyscus. Seeds were placed both in foraging towers (seen in the figure to the right), which resulted in elevated feeding sites, and on the ground. The results indicated that in the absence of predators, Peromyscus increased their level of foraging activity at the more exposed, elevated site. This may have been attributed to reduced rustling of leaf litter and greater visual acuity of the prey. Also, there was a reduction in foraging during a full moon as compared to a new moon; presumably the higher lunar light levels resulting in increased predation risk.
These experiments have been expanded to include foraging in shrubland and woodland. In the shrubland, we are examining how Peromyscus respond to visual, auditory, and olfactory cues and two spatial scales. In the oak woodland, we're using a similar suite of vertebrate cues, but measure variation in Peromyscus foraging in the open, long (run-ways), at the base of trees, and at elevated sites in tree trunks.
Foraging in the Tropics
This work is being conducted at Las Cuevas Field Station in Chiquibul Preserve, Belize. In numerous studies throughout North America, small mammals consistently used downed logs as foraging corridors. Many North American predators, such as foxes and owls hunt via auditory cues, and rustling leaves are a main attractant. This past summer, we compared how two disturbances – logging and hurricane – influence the structure of the rainforest and in turn small mammal foraging behavior. Although the sample size is still limited, we were very surprised to find that the small mammals completely avoided all downed logs, contrary to previous work in North America. Multiple encounters with tropical jumping pitvipers may be the explanation. Unlike mammalian or avian predators, pitvipers hunt via thermal and tactile cues. They commonly place their lower mandible on a log to sense vibrations. During future trips to Chiquibul, I hope to increase the sample size of tracked rodents and quantitatively analyze their movements in relation to downed woody material and vegetation structure.
Recent studies have focused on the the effects of urbanization on vertebrates. This has included a limited amount of work with anurans and birds. Our work with a variety of mammalian groups, including carnivores, small mammals, and bats, has taken a multifaceted approach. Population structure, community composition, and ecotoxicology are topics encompassed by current urbanization investigations; future collaborative work will incorporate population genetics.
Gradient analysis has been used to address questions on how urban sprawl
effects mammalian species distribution and abundance. The gradient, shown in the figure at left, starts near the "Lake Shore" of downtown Chicago
and ends 100 km away at Midewin National Tallgrass
Prairie, a 10,000 ha macrosite. Landcover along the gradient includes
dense residential areas (up to 3,200 people per square km), heavy
suburban subdivisions, extensive agriculture, and natural
From a systems perspective, I also have interests in wetland restorations. Projects have ranged from the distribution and abundance of frogs among a diversity of wetland types, to nested subset patterns of birds and a GIS model for predicting distribution of pre-settlement wetlands.
initiated work at a large scale nutrient farming project.
One question will focus on
experimental changes in hydrological regimes and the distribution and abundance
of muskrats. A second question will examine bioaccumulation of pesticides
and herbicides resulting from the increased flow of agricultural run-off. Funds are
also pending for a wet prairie restoration. This project will examine
different moisture regimes along a moisture gradient and how these abiotic parameters interact with herbivory.
[Photo yet to come]