Abstract
World-wide population declines have sharpened concern for amphibian conservation on working landscapes. Across the Sierra Nevada's national forest lands, where almost half of native amphibian species are considered at risk, permitted livestock grazing is a notably controversial agricultural activity. Cattle (Bos taurus) grazing is thought to degrade the quality, and thus reduce occupancy, of meadow breeding habitat for amphibian species of concern such as the endemic Yosemite toad (Anaxyrus [ = Bufo] canorus). However, there is currently little quantitative information correlating cattle grazing intensity, meadow breeding habitat quality, and toad use of meadow habitat. We surveyed biotic and abiotic factors influencing cattle utilization and toad occupancy across 24 Sierra Nevada meadows to establish these correlations and inform conservation planning efforts. We utilized both traditional regression models and Bayesian structural equation modeling to investigate potential drivers of meadow habitat use by cattle and Yosemite toads. Cattle use was negatively related to meadow wetness, while toad occupancy was positively related. In mid and late season (mid July–mid September) grazing periods, cattle selected for higher forage quality diets associated with vegetation in relatively drier meadows, whereas toads were more prevalent in wetter meadows. Because cattle and toads largely occupied divergent zones along the moisture gradient, the potential for indirect or direct negative effects is likely minimized via a partitioning of the meadow habitat. During the early season, when habitat use overlap was highest, overall low grazing levels resulted in no detectable impacts on toad occupancy. Bayesian structural equation analyses supported the hypothesis that meadow hydrology influenced toad meadow occupancy, while cattle grazing intensity did not. These findings suggest cattle production and amphibian conservation can be compatible goals within this working landscape.
Highlights
Amphibian conservation is gaining considerable attention as a result of increasing quantitative evidence of global population declines [1,2]
In the Sierra Nevada, nearly half of the native amphibian species are considered at risk by state and federal regulatory agencies [3,4,5,6]
In order to provide proof of concept, supporting the construction of the general conceptual diagram for structural equation analyses, we examined the following bivariate relationships via multiple regression analyses: 1) meadow wetness and toad meadow occupancy rates, peak biomass production, herbaceous biomass use, and fecal loading; 2) fecal pat density and herbaceous biomass use, and 3) forage quality metrics and meadow wetness
Summary
Amphibian conservation is gaining considerable attention as a result of increasing quantitative evidence of global population declines [1,2]. Infectious diseases, climate change, and anthropogenic land-use changes such as urbanization and agriculture have all been identified as potential drivers of amphibian declines [7]. Cattle grazing (Bos taurus), a prominent agricultural activity in the Sierra Nevada region, has received growing interest as a potential driver [8,9,10,11,12,13,14,15], and has been implicated in amphibian species declines in the Sierra Nevada [4,5,6,16]. 1,950 m to 3,450 m) in the central and southern Sierra Nevada [20,21] These mountain meadow habitats exhibit a range of hydrologic conditions varying from scattered, ephemeral pools to expansive, season-long flooded areas, which differentially support toad breeding and rearing habitats
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