title: Potential effects of environmental contamination on Yuma Myotis demography and population growth.
abstract: Unplanned natural and anthropogenic disasters provide unique opportunities for investigating the influence of perturbations on population vital rates and species recovery times. We investigated the potential effects of a major pesticide spill by comparing annual survival rates using mark-recapture techniques on a riparian bat species, Yuma Myotis (Myotis yumanensis). Demography and population dynamics for most bat species remain poorly understood despite advances in mark-recapture estimation and modeling techniques. We compared survival and population growth rates of two roost populations exposed to a large chemical (metam sodium) spill in the upper Sacramento River in Northern California with two roost populations outside the contaminated area from 1992 to 1996. Hypotheses about long-term effects of the spill on female juvenile and adult survival were tested using an information-theoretic approach (AIC). Working hypotheses included effects of age, chemical spill, and time trend on survival. Female adult survival was higher than female juvenile survival across all sites, suggesting stage-specific mortality risks. Model-averaged estimates of female juvenile survival in the contaminated area (0.50-0.74) were lower than in control roosts (0.60-0.78) for each year in the study, suggesting that the spill may have reduced juvenile survival for several years. Female adult survival (0.73-0.89) did not appear to be strongly affected by the spill during the years of the study. There was an increase in survival for both stage-classes across all populations during the study period, which may have been caused by the end of an extended drought in California in the winter of 1993. The spill-affected population was in decline for the first year of the study as indicated by an estimated growth rate (lambda) < 1, but population growth rates increased during the four-year period.
authors.affiliation: Department of Forest Science, Oregon State University, Corvallis, Oregon 97331, USA. Winifred.Frick@oregonstate.edu
authors.forename: Winifred F
authors.initials: WF
authors.lastname: Frick
authors.forename: William E
authors.initials: WE
authors.lastname: Rainey
authors.forename: Elizabeth D
authors.initials: ED
authors.lastname: Pierson
mesh_terms: D000818:Animals; D002140:California; D002685:Chiroptera / Q000254:growth & development; D003710:Demography; D004785:Environmental Pollutants / Q000633:toxicity*; D005260:Female; D011158:Population Growth; D015996:Survival Rate
chemical_list: D004785:Environmental Pollutants