Observations of animal distributions have revealed that population densities have tracked resource quality. Various models have been proposed to account for such “resource matching.” For example, the Ideal Free Distribution (Fretwell and Lucas 1970) model employs habitat selection rules which assume mobile animals evaluate available habitat patches and select the highest quality patch first. I examined movement patterns of northern crayfish (Orconectes virilis) in response to habitat patches of different quality to test this assumption. I found that animals were more likely to leave a low quality patch than a high quality patch even when there were no other patches available, suggesting that the quality of encountered resources plays a significant role in subsequent decisions about movement. However, many animals did not leave the first patch they encountered, even when better habitat existed elsewhere and was well within their ability to sample it. Finally, not all crayfish selected the best site they encountered. My studies demonstrate that the response to resources is complex, and IFDs and other distribution models may rely on overly simplified assumptions about habitat selection behavior.

Life history strategies encompass a suite of co-evolved traits crucial for ensuring an individual's fitness, often evolving from trade-offs between traits competing for the same resources. Adult male crayfish in the Cambaridae family undergo seasonal morphological changes linked to reproductive status, a process called cyclic dimorphism. In this dissertation, we attempt to understand how cyclic dimorphism evolved in non-native northern crayfish (Faxonius virilis). First, in Chapter 1, we review empirical studies that have assessed animal personality across developmental periods. The results show that personality traits tend to be stable within life stages but not across developmental events. In Chapter 2, we examine growth patterns to investigate a potential trade-off between energy allocation for body size growth versus chelae size growth. We show a larger carapace length growth increment in nonreproductive crayfish and a larger growth increment in chelae length in reproductive crayfish. In Chapter 3, we investigate the interaction between behavior and various physiological traits. We find that nonreproductive crayfish had a higher metabolic rate and were in better body condition than reproductive crayfish. We also find that crayfish with higher energy stores tend to be in better body condition. Finally, in Chapter 4 we use two separate crayfish groups to test three hypotheses to understand how energy is used to finance growth. We show that nonreproductive crayfish in the wild tend to consume more food and have more energy stores than reproductive crayfish. We also show that nonreproductive captive crayfish tend to have more energy stores than reproductive crayfish. The work contained in this dissertation contributes to the understanding of the relationship between behavior and physiology and its implications on the evolution of complex life histories.