This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: 1. In the article by Holekamp and Sherman the authors investigate the dispersal of male ground squirrels and tested several hypotheses for each of the 4 levels of analysis. Write one of the hypotheses that the authors proposed for each level of analysis, their predictions and the methods used to test each of them. ***NOTE*** Results of each hypothesis is not required for this question, but you may find the results on Pg. 59 in the table. Physiological Mechanisms - Level of Analysis (Pg. 55) Overall Hypothesis: Gonadal steroids may mediate natal dispersal. (They tested for organizational vs. activational effects of androgens. Hypothesis I: Activational hypothesis, levels of androgens should be elevated in juvenile males at the time of natal dispersal. Prediction: In the absence of androgens, males should not disperse. Methods: Blood samples from male pups born and reared in the laboratory were drawn every few weeks for 4 months. Field experiment portion consisted of a number of females and males being gonadectomized (removal of ovaries or testes), then released into natal burrow and dispersal behavior was monitored. Hypothesis II: Organizational hypothesis, exposing perinatal or neonatal females to androgens should masculinize subsequent behavior, including natal dispersal. Prediction: Females should natally disperse when expose to androgens. Methods: Pregnant females were captured and housed until given birth. Female pups were injected with a small amount of testosterone with a control group being given oil only. Mothers and pups were then released back to the field. Onotogenetic Processes - Level of Analysis (Pg. 56-57) Ontogenetic-Switch Hypothesis: Dispersal is triggered by endogenous (internal) factors. Males may stay home until they attained sufficient size or energy reserves to permit survival during rigors of emigration. Prediction: Juvenile males will disperse when they attain a threshold body mass and that dispersers should be heavier, or exhibit different patterns of weight gain, than predispersal males of equivalent ages. Methods: Observation in the field. Effects on Fitness Level of Analysis (Pg. 57-58) Hypothesis: Natal dispersal might enable juvenile males to avoid fitness costs associated with life in the natal area and might allow them to obtain benefits elsewhere such as food shortage. Prediction: If natal dispersal occurs because of food shortages, then juveniles whose natal burrow is surrounded by abundant food should be more philopatric (tendency of a migrating animal to return to a specific location in order to breed or feed) than those from...
View Full Document
This note was uploaded on 02/17/2010 for the course BIO 359K taught by Professor Mcclelland during the Spring '08 term at University of Texas at Austin.
- Spring '08