Sexual size dimorphism in species with asymptotic growth after maturity

If animals mature at small sizes and then grow to larger asymptotic sizes, many factors can affect male and female size distributions. Standard growth equations can be used to study the processes affecting sexual size dimorphism in species with asymptotic growth after maturity. This paper first outlines the effects of sex differences in growth and maturation patterns on the direction and degree of sexual dimorphism. The next section considers the effects of variation in age structure or growth rates on adult body sizes and sexual size dimorphism. Field data from a crustacean, fish, lizard and mammal show how information on a species' growth and maturation patterns can be used to predict the relationships between male size, female size and sexual size dimorphism expected if a series of samples from the same population simply differed with respect to their ages or growth rates. The last section considers ecological or behavioural factors with different effects on the growth, maturation, survival or movement patterns of the two sexes. This study supports earlier suggestions that information on growth and maturation patterns may be useful, if not essential, for comparative studies of sexual size dimorphism in taxa with asymptotic growth after maturity.     

The Effects of Habitat Geometry on Territorial Defense Costs: Intruder Pressure in Bounded Habitats

Computer simulation models were used to explore the effect ofhabitat geometry on intruder pressure for territories in differentlocations within a patch of uniformly high quality habitat,for territories in patches of different shapes and sizes, andfor patches surrounded by different types of suboptimal habitats. In models in which the edges of the habitat patch are impermeable(hard-edged), intruders do not leave the central territorialhabitat, H, and intruder pressure is lower for territories onthe edge of H than for more centrally located territories. Averageintruder pressure for any given loop of territories (, for loop = i) is positively relatedto both the proportion of territories on the edge of the patch(ESR) and the average distance moved by intruders. In models in which the edges of H are permeable (soft-edged),intruders are able to move between H and the surrounding habitats,which were of two types: sinks (no intruders generated there)and reserves (a source of intruders). The presence of sinksdramatically reduces both and average intruder pressure over H () as compared to hard-edged habitats, and both and are negatively related to the proportion of territories on theedge of the patch (ESR). Conversely, and are positively related to ESR when the surrounding habitat acts as an intruder-reserve. Data from empirical studies of territorial species agree withmany of the direct and indirect qualitative predictions of thesemodels. The effects of habitat geometry on defense costs maybe important in many territorial species, and should be takeninto account in future studies.     

Why Evolutionary Issues are Reviving Interest in Proximate Behavioral Mechanisms

Information about proximate behavioral mechanisms is requiredto answer a variety of important questions about the evolutionof behavioral and other traits. For instance, theoretical studiesof maternal effects indicate that the behavior of parents mayhave profound effects on the evolution of phenotypic traitsin their offspring, and that maternal effects may provide nongeneticpathways for the inheritance of both behavioral and nonbehavioraltraits. Similarly, the recent emphasis on genetic correlationsamong traits cautions that correlations among behavioral traitsmay have surprising effects on behavioral evolution, and providesfurther impetus for studies of the proximate bases of behavioraltrait syndromes. Finally, the literature on information acquisitionsuggests that the behavioral processes used in assessment mayaffect the evolution of behavioral and other traits. For instance,if information is costly to obtain, individuals may prefer familiarto unfamiliar situations. In a social context, a preferencefor familiar individuals could have a variety of effects onthe evolution of social and nonsocial behavior patterns. Theseand other examples suggest that interest in behavioral processeswill continue to grow during the next decade, and that proximateand ultimate approaches to behavioral problems will be moreclosely integrated than was true in the past.