"Predator's view" of fragmentation

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Related to my interests in population dynamics at the landscape level, is my interest in the mechanisms that relate mortality to ground nesting birds like waterfowl, pheasants, and passerines to mammalian predation. So I was naturally led to interest in the "predators' view" of habitat fragmentation, especially how they move in relation to features like wetlands, edges, and other discontinuities in the landscape.

red fox

Photo by Brian Allen

We started by studying relationships among mammalian predators and waterfowl in landscapes of the northern Great Plains, in cooperation with Dr. Marsha Sovada from Northern Prairie Wildlife Research Center and Dr. Rolf Koford. We have finished studies based on intensive telemetry data of movements of red fox and striped skunk that were supported by the Institute for Wetland and Waterfowl Research. We mapped foraging paths in relation to duck nests and landscape features. The image at right shows one of our radioed foxes with an egg that it has just taken from a duck nest.

Because much of the mortality to ground nesting birds like waterfowl, pheasants, and passerines is the result of mammalian predation, I was naturally led to study how predators' and prey view habitat fragmentation. We have studied spatial relationships among nesting birds, predators, and alternate prey.

We are applying habitat selection theory and spatial analytical tools to predict how predators move as a function of landscape features such as distances between wetland and grassland patches, patch size, shape, and edge characteristics.

Allen Hills West graph

One of the toughest aspects of the problem is to understand how predators move as a function of landscape features such as distances between wetland and grassland patches, patch size, shape, and edge characteristics. With further support from IWWR and in collaboration with Philip Dixon of Statistics we are applying habitat selection theory and spatial analytical tools to this problem. Using the IWWR assessment data, like the Allen Hills site in Saskatchewan (map to right) we have modeled waterfowl nests as a spatial point pattern by calculating a transformed Ripley’s K-function (L = 0 represents randomness). After accounting for patch edges, internal wetlands, and habitat nesting preferences of ducks the plot shows that the observed nests are aggregated, or clumped, at scales of ~100-300 meters (the hump in the figure below) and indistinguishable from random at all other distances.

Complex-L-Funcation graph nest destruction graph

Predators have to discover nests in both space and time, so we have to account for temporal as well as spatial dependence in nest destruction by calculating a space-time K-function (D-zero plot to right). This example shows a peak at short spatial and temporal scales demonstrating that nests close in both space and time have a higher probability of destruction.

cowpie and grubs

We also conducted spatial analyses of predator movements overlaid on nesting locations. These analyses were based on field data that has appeared in a series of publications from the ND work. By assessing overlap of predator movements and nesting locations we will attempt to model the probability of nest destruction under various landscape conditions.

A final dimension of the predator prey work concerns availability of alternate prey. For example, striped skunks forage through the agricultural edges and pastures for grubs.

Molly

We focused on small mammals that are especially important prey to fox, skunk, badger, and weasel. Besides conducting standard mark-recapture studies.   Another dimension of our North Dakota predator-prey studies has been to consider the effects of alternate prey, especially small mammals, on waterfowl nesting success.

Eventually this cooperation with scientists from Ducks Unlimited and USGS will help to link land use, wetland conditions, predator populations, small mammals, and dynamics of waterfowl productivity. Such work is a priority of management agencies and part of DU's research efforts in the northern Great Plains.

mammal predators (click for larger image)biomass graph (click for detailed image)
small mammal trap (click for larger image)

We also assessed track tubes as a means to monitor small mammal populations.  We conducted mark-recapture surveys and track tube surveys in upland grasslands and near wetlands.

 

Updated 8/9/11