Ecological memory in farmed landscapes: empirical models of amphibian communities in Palouse prairie wetlands

Erim Gomez

Ecological memory is a metaphor for patterns of historical biodiversity and ecological structure and function that are detectable within modified landscapes, and therefore are key to understanding possibilities for future ecological restoration in human dominated landscapes. Ecological memory may include different biological and ecological legacies, including genetic composition, historical species diversity, soils and hydrologic patterns, habitat connectivity, and many other factors important in conserving and restoring species. Palouse Prairie has lost about 97% of its original wet meadows and wetlands to intensive farming, and now is one of the most endangered grassland ecosystems in North America, making it a useful system for studying ecological memory and conservation in highly modified landscapes. We evaluated evidence for ecological memory in wetland landscapes in Palouse Prairie by: 1) describing amphibian diversity and abundance in contemporary wetlands, and 2) sampling selected landscape and wetland habitat variables to construct descriptive ecological models to characterize amphibian distribution and occurrence in wetlands across a Palouse Prairie landscape. We used classification and regression trees and boosted trees (i.e., algorithmic regression techniques) to develop ecological models predicting the occurrence of over 4000 amphibian larvae of 7 species captured in 63 wetlands during 2009 along a geographic gradient extending from the Palouse Prairie bioregion in eastern Washington, to Moses Lake in the Columbia Basin of central Washington. No obvious natural wetland basins were observed among the 63 wetlands surveyed in Palouse Prairie, and all amphibians occurred in wetlands that were constructed or modified by human development in some way. Both types of tree modeling platforms frequently used different sets of predictive variables, but generally included: a) presence or absence of introduced fish, b) wetland type and size, c) surrounding landscape context, and d) broad geographic patterns. However, both models accurately predicted occurrence of amphibian species in wetlands. All amphibian species showed a strong negative association with fish, except for invasive bullfrogs. Despite intensive farming, ecological models of contemporary amphibian populations showed that Palouse Prairie wetlands might retain elements of ecological memory inferred from biogeographic distribution and landscape ecology. These empirical models may better inform and greatly improve future ecological restoration.

Ecological memory in farmed landscapes: empirical models of amphibian communities in Palouse prairie wetlands

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