UVM Theses and Dissertations
Format:
Print
Author:
Newman, Nathaniel J.
Title:
Dept./Program:
Biology
Year:
2010
Degree:
MS
Abstract:
This research investigatedthe causes of variation in worker body size in the desert seed-harvesting ant Messor pergandei. The work was conducted at sites dispersed throughout the species' range in the Mojave and Sonoran Deserts in the United States. Two hypotheses were tested: 1) that worker size variability results ffom character displacement driven by interspecific competition, and 2) that worker size variability is caused by fluctuations in the availability of colony food resources. The character displacement hypothesis predicts that worker size distributions within study sites will remain stable over time, while the results showed that they differed significantly and substantially from year to year.
Moreover, the character displacement hypothesis predicts that natural selection to reduce competition among species should result in minimal current overlap in the body size of M. pergandei with competing species of seed harvesting ants. The results showed that there was substantial current overlap in body size at a number of sites that were originally studied in formulating the hypothesis. These results suggest that character displacement is not the primary factor that explains worker size variation in M. pergandei. Alternatively, the resource abundance hypothesis, which proposes that worker size is determined by the abundance of seeds available to the individual colony, does garner support. The primary evidence for this is a significant positive correlation between worker size and estimated seed abundance at study sites over a two-year period.
This result is also consistent with an earlier study in the Sonoran Desert showing that worker body size varies seasonally according to hypothesized resource fluctuations, suggesting that variation in the body size of M. pergandei workers can best be explained by the ebb and flow of available resources over time and space. It further suggests that it is less costly to the colony to produce small workers, and the ability to vary the size ofworkers is an adaptive advantage to M. pergandei that enables them to populate some ofthe most extreme and variable landscape in North America by adjusting their resource needs according to seasonal and global trends.
Moreover, the character displacement hypothesis predicts that natural selection to reduce competition among species should result in minimal current overlap in the body size of M. pergandei with competing species of seed harvesting ants. The results showed that there was substantial current overlap in body size at a number of sites that were originally studied in formulating the hypothesis. These results suggest that character displacement is not the primary factor that explains worker size variation in M. pergandei. Alternatively, the resource abundance hypothesis, which proposes that worker size is determined by the abundance of seeds available to the individual colony, does garner support. The primary evidence for this is a significant positive correlation between worker size and estimated seed abundance at study sites over a two-year period.
This result is also consistent with an earlier study in the Sonoran Desert showing that worker body size varies seasonally according to hypothesized resource fluctuations, suggesting that variation in the body size of M. pergandei workers can best be explained by the ebb and flow of available resources over time and space. It further suggests that it is less costly to the colony to produce small workers, and the ability to vary the size ofworkers is an adaptive advantage to M. pergandei that enables them to populate some ofthe most extreme and variable landscape in North America by adjusting their resource needs according to seasonal and global trends.