UBC Theses and Dissertations
Effects of habitat and food on demographic classes and population dynamics of a habitat specialist, the rock mouse Galindo Leal, Carlos
I examined the relations between habitat structure, population variability and patterns of microhabitat use by demographic classes (sex, age, residency) in the rock mouse in southern Durango, Mexico. I also examined individual and population responses to experimental changes in food abundance, and the consequences for the prevalence of botfly parasitism. I used a gradient of habitats in manzanita-oak shrubland to analyze demographic variability and microhabitat use patterns. If demographic parameters of habitat specialists are closely associated with habitat structure, I expected populations to be more similar in habitats with matching habitat structure. Demographic characteristics were more dissimilar in those grids with the greatest differences in vegetation characteristics. I also tested the hypothesis that populations with higher breeding densities have higher adult survival, lower recruitment and higher stability. The areas with highest breeding densities had low juvenile and subadult recruitment in the breeding season. Both were relatively stable during the first year of study, but one declined to extinction during the second year. I examined microhabitat use by individuals to test the hypothesis that demographic classes differ in their spatial distribution, particularly during the breeding season. There were differences in microhabitat use among sexes and ages, as well as among resident and transient individuals, particularly in the breeding season. I conducted two short-term (4 mo) supplementary food addition experiments during breeding and non-breeding seasons to test the hypothesis that females are more responsive to food resources than males, especially during reproduction. In two grids I added food on relatively widely spaced point sources to compare the effects within grids on fed and unfed subpopulations. I also compared the populations on treatment grids and on a control grid. Among fed subpopulations females responded more intensely to food additions than males. They gained weight and had improved reproduction and improved survival, during both wet and dry seasons. Males responded less consistently than females. There were also substantial effects at the population level. Populations on both experimental grids increased as a result of the food addition. Reproduction and adult recruitment also improved. Lastly, I tested the hypothesis that botfly infestation is male-biased and related to increased movement. Sexes differed seasonally in infestation rates. During both years adult females were heavily infested in the fall, whereas adult males were mainly infested in winter. Infestation rates were negatively related to motility. Females had higher infestation in the breeding season when they move less, whereas males had higher infestation in the non-breeding season. In the experimental grids higher infestation rates occurred among individuals, particularly females, who used traps near food stations.
Item Citations and Data