The Effect Of Selenium On Reproduction Of Black Tailed Deer Odocoileus Hemionus Columbianus In Shasta County California

Author : Tavis Donahue Forrester
Publisher :
ISBN 13 : 9781321608526
Total Pages : pages
Book Rating : 4.6/5 (85 download)

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Download or read book Effects of Predation and Forage Availability on the Survival of Black-tailed Deer (Odocoileus Hemionus Columbianus) in the Mendocino National Forest, California written by Tavis Donahue Forrester and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Mule (Odocoileus hemionus) and black-tailed deer (O. h. columbianus) have exhibited marked population fluctuations throughout their range over the past century. The relative contributions of predation, forage availability, and weather to observed population changes remain unclear and controversial. I evaluated the effects of both predation and forage on the survival of mule and black-tailed deer though a literature review and extensive field research in the Mendocino National Forest from 2009-2013. I reviewed 48 studies on mule deer survival and predation from the past 30 years and quantified age-specific vital rates, population growth rates (lamda) and causes of mortality. I also evaluated the effect of environmental variables on variation in vital rates and the contribution of age-specific survival to population growth. Age-specific survival (Phi) was the most frequently studied population parameter. Mule deer have lower and more variable fawn survival than other ungulate species (Phi(summer)=0.44, CV=0.42; Phi(annual)=0.29, CV=0.67). Adult female survival conversely appeared to be high and stable throughout the geographical range of the species (Phi(annual)=0.84, CV=0.06). Observed low fawn survival appears to be compensated for by high fecundity rates. Predation was the primary proximate cause of mortality for all age classes, and was an important source of summer fawn mortality and of mortality in multi-prey, multi-predator systems. However, predator removal studies suggest that predation is compensatory, particularly at high deer densities, and that nutrition and weather shape population dynamics. I propose three models to explain local population dynamics of mule deer: a) populations are limited by forage availability and weather; b) adult females are limited by forage availability, fawns are limited by forage availability and predation, and population growth is constrained by fecundity and fawn predation; and c) large changes in the abundance of predators or alternative prey change predation risk and destabilize population dynamics. From 2009 to 2013, I led field crews that captured and monitored 135 black-tailed deer fawns in coastal California to study possible interactions between forage and predation on survival. I estimated seasonal and annual survival rates, assessed the cause of all mortalities (n=95), measured available forage, estimated relative abundances of predators on summer range (i.e., fawning areas) each year, and used remote sensing to quantify habitat on winter range. I then used cumulative incidence and proportional hazards functions to evaluate how environmental covariates were related to fawn survival. Summer survival rates averaged 0.40 across all years (SE=0.05) and the mean annual survival rate was 0.25 (SE=0.04). I found that most fawn mortality resulted from predation during summer, mainly by black bears (Ursus americanus) and coyotes (Canis latrans), and spatial differences in summer survival persisted until recruitment. Black bear predation, the single largest cause of mortality, was unrelated to forage availability. Observed spatial variation in mortality risk due to other causes was linked to the availability of oak forage but not predator abundance. Additionally, characteristics of deer including adult female condition and fawn birthweight, did not provide evidence for purely bottom-up limitation. Rather my results provided evidence that both bottom-up and top-down effects were influencing fawn survival in this declining population, and that predator identity and the timing of mortality affected these interactions. I also tracked 57 adult female black-tailed deer using GPS collars and radio-telemetry to determine seasonal movements and home ranges and monitor survival and cause of mortality. I used the seasonal home range as a measure of site familiarity and modeled how mortality risk varied with use of familiar areas, forage availability, age class, and elevational overlap with simultaneously collared pumas using Cox proportional hazards models. Adult female survival was low in our study area (0.70 vs. 0.84 species average), and predation was the largest cause of mortality. The use of familiar areas was the best predictor of mortality risk, and deer that had a 40% chance of leaving the home range in a given week were 4 times more likely to die. Puma predation was the largest cause of mortality and deer whose average weekly elevation was farther from the average elevation of pumas were less likely to die. While forage availability was not related to mortality risk, adult females with lower forage availability were more likely to leave their home range in both summer and winter. I found fitness benefits of using familiar areas and bottom-up effects on the use of familiar areas as a refuge from predation. The benefits of site familiarity are likely widespread in ungulates, especially when there are stable home ranges, complex habitats, and unclear cues of predation risk. My results provide evidence that both bottom-up and top-down effects were influencing black-tailed deer survival in this declining population, and that predator identity, the timing of mortality, and individual behavior affected these interactions.