Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
Browse
2 results
Search Results
Item Proximate mechanisms and ultimate causes of female reproductive skew in cooperatively breeding golden lion tamarins, Leontopithecus rosalia(2011) Henry, MaLinda Dawn; Dietz, James M; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many cooperatively breeding species exhibit high reproductive skew. Delayed dispersal and cooperative breeding may have evolved as a consequence of the limits ecological constraints place on independent breeding. When simultaneous breeding by multiple females reduces the survival of the dominant's offspring, selection should favor dominants able to control subordinate reproduction. Monopolization of reproduction by dominant group members by means of suppression of subordinate reproduction has been documented in several taxa of cooperative breeders. In this dissertation I examine the proximate mechanisms and ultimate causes of reproductive skew in cooperatively breeding golden lion tamarins (Leontopithecus rosalia). In chapter one I combine data from phenological transects with hormonal evaluation of reproductive status to test whether caloric availability limits reproduction by female tamarins. Caloric availability was sufficient to support not only pregnancy polygyny in 83% of tamarin groups, but also the additional group members resulting from multiple litters. The super abundance of calories and the timing of births suggested that competition for allocare rather than for food resources may be the selective force limiting reproduction by subordinate females. In my second chapter I combine hormonal and demographic data to explain reproductive skew in terms of the costs and benefits to subordinate fitness under existing social circumstances. Subordinate females older than 18 months of age ovulated while residing within their natal group, but conceptions were delayed one to two years following reproductive maturity. The likelihood of successful reproduction by a subordinate female doubled with each year of age of the dominant female. Conceptions under incestuous mating conditions were rare (7 of 37 pregnancies). My results provide support for the hypothesis that subordinate adult females under three years old exercise reproductive self-restraint. I speculate that the threat of being evicted from the group and inbreeding avoidance are sufficient to delay attempts at reproduction by young subordinates without the need for costly fighting with the dominant female. In my third chapter I test whether reproduction by subordinate adult female tamarins is limited by dominant females who have incomplete control (incomplete control model, ICM) or complete control (optimal skew model, OSM) over subordinate reproduction. I combine hormonal data with group demography and caloric availability to determine variables useful in predicting a successful pregnancy to a subordinate female. Whereas subordinate females younger than 2.5 years of age ovulated but did not conceive, all females older than 3.9 years of age became pregnant. Reproduction in subordinate adult females was not limited by hormonal suppression of ovulation or conception, but by the failure of 7 of 11 pregnancies to produce live offspring. The likelihood of reproductive success increased 1.7 times with each additional group member. My results suggest that when caloric availability is sufficient to support reproduction by two breeding females and the group members necessary to provide allocare for two litters, subordinate females do not abide by a social contract that would limit their reproduction (OSM). Instead, older subordinates compete with dominant females for reproduction and succeed in producing live young if the dominant female is at least 10 years old, if subordinates conceive while the dominant is heavily pregnant, and if they reside within larger groups (ICM).Item Resource and space use in the wild golden lion tamarin, Leontopithecus rosalia(2008-11-11) Hankerson, Sarah; Dietz, James M; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Animals move through their environment in response to resource, competitor, and predator distribution. In this dissertation I examine resource and space use in wild golden lion tamarins (GLTs, Leontopithecus rosalia). In chapter one I present the results of a field study exploring factors predicting sleeping site selection. GLTs preferentially slept in tree holes. Each group had a few frequently used sites typically found in large, living trees on hillsides near other large trees. Topography and smallscale forest and tree variables were better than habitat-level classifications in predicting sleeping site use. In my second chapter I evaluated home range calculation methods. Using 19 years of data for 15 groups of GLTs, I calculated a yearly home range for each group with the three most commonly used methods: minimum convex polygon (MCP), grid cell, and kernel density estimates. MCP produced the largest home range estimates, grid cell the smallest, and kernel estimates were intermediary. Kernel estimates were preferred because probability of use may be calculated for any part of the home range, there is high concordance between observation spatial distribution and home range shape, and there is a lack of relationship between sample size and home range size. In my third chapter I tested three hypotheses explaining home range size in group-dwelling animals. First, I tested the dominant hypothesis, which states that home range size is determined by group energetic needs and, therefore, group size. The second and third hypotheses relate to numbers of adult females and males present in groups. More adults may increase ranging because of increased reproduction, search for breeding opportunities, or defense. I also examined how variation in predation affects population density and demography and, thus, mediates space use. I found support for all three hypotheses. Larger ranges were occupied by groups that were large, had two breeding females, and/or more potentially breeding males or adult natal males. Intense predation resulted in lower population densities, smaller groups, only one breeding female per group, and fewer adult natal males. Population density and predation had significant, negative impacts on home range size.