No-till farming is an important approach to sustainable agriculture because it can conserve soil and water resources. Unfortunately, rodent populations can thrive under no-till conditions because burrow systems are not disrupted by annual plowing and plant residues build-up on the surface, providing cover and insulation. This can result in substantial crop damage. We assessed rodent populations, habitat use, food habits, and crop damage in a no-till cropping system in Washington, USA. We also conducted preliminary trials of methods to reduce rodent populations and crop damage. In the fall, many more rodents were captured in fields with unharvested crops than in fields containing only plant stubble, suggesting that rodents leave fields after crop harvest, providing that suitable habitats are nearby, even when adequate cover is still available in harvested crop fields. By spring, the number of voles captured was much lower relative to fall. Despite this, capture rates were much higher in surrounding permanent grass areas than in crop (barley, wheat, pea) fields, suggesting that these grassy areas serve as refugia for rodents. Furthermore, the permanent grass cover type was the landscape variable most associated with rodent capture rates. In three winter pea fields, rodents removed 5-15% of the pea plants over winter. Examination of stomach contents revealed that voles mainly fed on grain plants in spring, but that their diet was more diversified in fall. Deer mice fed heavily on grain plants in both spring and fall, but also used insects as food. Metal barrier exclosures (9 m × 9 m), extending above and below ground, did not prevent access by rodents. Rodent populations in areas treated with zinc phosphide on grain were comparable to untreated areas 1 year after application of the rodenticide, perhaps because of immigration and recruitment, suggesting that baiting does not provide a long-term solution to rodent damage in no-till agricultural fields.
Captive breeding has become globally important in endangered species recovery, yet it is fraught with problems such as maintenance of genetic diversity, and adaptation to captivity. We studied survival and population dynamics of a captive population of endangered Columbia Basin pygmy rabbits Brachylagus idahoensis, from 2003 to 2007, to evaluate its potential for supporting reintroduction and recovery of wild extirpated populations in shrub-steppe ecosystems of eastern Washington, USA. We developed stochastic population viability analysis models in Vortex and RAMAS to assess performance and surplus production of the captive population. This pygmy rabbit population has low adult survival beyond 1 year and dependency on high juvenile recruitment for population growth. Low juvenile survival and high variability in stochastic growth rates result in high variability in annual productivity. Our analysis showed that the captive population at n = 75 cannot sustain a steady annual harvest of Z30 rabbits for reintroduction and supplementation without increasing the risk of quasi-extinction (n = 30) to 59%. We conducted sensitivity analysis on maternity, carrying capacity and survival rates to identify critical values for model parameters that would lower extinction risk to the captive population when used as a source of rabbits for reintroduction. Increasing juvenile survival and recruitment into the first breeding class is the most effective method for enhancing the breeding program. Our population models suggest that captive breeding and recovery programs for short-lived lagomorphs present significant conservation challenges because of the need to rapidly grow such populations to overcome demographic and genetic challenges.
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