||Snake populations in the North American tallgrass prairie appear to be declining,
yet data unavailability impedes the development of enhanced ecological understanding
of snake species-habitat relationships and also hinders snake conservation efforts.
This study addresses both issues for the snakes of Illinois in two steps.
In a two-year mark-recapture study at twenty-two sites within six northern Illinois
prairie preserves, I investigated snake species-habitat relationships using habitat
variables at three scales: microhabitat (< 100 m), landscape (1 - 10 km), and regional
(> 10 km). A total of 120 snakes representing seven species was captured using drift
fence arrays associated with funnel traps and sheet metal cover. The low numbers and
diversity of snakes captured, when compared to historic evidence, indicate that Illinois
snake populations have declined.
At the microhabitat scale, non-metric multidimensional scaling and Mantel tests revealed
a relationship between snake species composition and elevation. At the landscape-scale,
snake species composition varied along an agricultural-urban cover gradient. Classification
and regression trees and maximum entropy models (Maxent) were used to identify the
scales at which snake species-habitat relationships were strongest. Six of seven regression
trees for individual snakes species contained habitat variables at the landscape scale.
Important landscape characteristics included patch size, isolation, and land cover,
metrics that strongly covary with habitat loss. Microhabitat features only appeared
in the regression trees of two species and in three Maxent models. This study indicates
that habitat loss has shaped the current distribution of snake species in Illinois's
remnant prairies and that snake conservation efforts should emphasize the landscape-scale.
Finally, I developed a risk ranking system based on natural and life history characteristics
to assess the conservation status of Illinois's 38 snake species. Cluster analysis
identified eight groups of snakes, similar in terms of risk factors, with high risk
species sharing characteristics such as large body size, long life span, limited habitat
breadth, and a high anthropogenic threat ranking. Here, I emphasize the need for
basic demographic studies on snakes and suggest that ranking systems be used with
population data (when available) and expert opinion to identify snake species of conservation
concern in other regions.