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There is no abstract available for this dissertation.

Because pronatalist sentiments may be an important aspect of Mexican-American ethnic heritage, this research focuses on cultural as well as socioeconomic factors which may contribute to higher Mexican-American fertility. Language use and nativity are used as indirect indicators of identification with an ethnic culture. Wives' characteristics are generally considered adequate to the study of couples' fertility, but in light of earlier research by the author indicating the importance of cultural factors to the fertility expectations of Mexican-American adolescent males, characteristics of husbands as well as wives are included in this analysis. For this reason, the sample, which is drawn from the 1980 Census data for Arizona, Texas, and New Mexico, is limited to Mexican-American and Anglo women who have been married only once and live with their husbands. Two complementary methods of analysis are used. Linear regression describes the significance of husband's and wife's language use, nativity, and socioeconomic characteristics to mean family size. Parity progression ratios are used to study the contribution of these variables to the likelihood of the addition of one more child at each stage of the family building process. While wife's characteristics are sufficient to account for most of the variation observed in Anglo fertility, husband's socioeconomic characteristics significantly contribute to variation observed in the fertility of Mexican-American couples. Husbands' identification with Mexican-American culture may be somewhat more important to couples' fertility than that of their wives. This is consistent with research which suggests that children are more central to male sex role expectations as they are expressed in the context of Mexican-American culture than in that of Anglos. The measures of ethnic identity used in this study are clearly associated with socioeconomic status. The differential fertility of Anglos and Mexican Americans could be attributed to these differences. The association of Spanish language use and fertility has been linked to the lower opportunity costs represented by additional children to women who do not speak English proficiently. However, the analysis of these data, which compares structural and cultural explanations of fertility differentials, provides evidence of cultural effects as well as the effects of socioeconomic status on fertility.

Varying numbers of adult desert pupfish (Cyprinodon macularius) and mosquitofish (Gambusia affinis) were introduced separately into experimental habitats open to egress to determine resource requirements for each species and the relation between numbers and resources. Laboratory environments in which "voluntary" colonization was achieved, were created for both species. Results indicated that both species have the innate ability to regulate numbers in their respective populations to available resources via emigration. The number of resident fish varied directly with experimental reductions of cover. When adult mosquitofish were introduced into open tanks with established populations of adult desert pupfish in habitats containing constant resources, there was no significant change in population size for either species as compared to single species populations over a 5-day period. Adult desert pupfish and mosquitofish are able to coexist successfully in habitats open to egress for 5 days because they utilize available resources in very different ways and the number of fish that become residents do not go beyond resource limits. These data suggest that replacement of desert pupfish by mosquitofish in the American Southwest is a phenomenon that is the result of more long-term interactions between all life stages of the species and may be more likely to occur in environments of low complexity and closed to egress.