Agonistic behavior and costs of aggression in decapod crustaceans
Animals that engage in aggressive behavior necessarily incur some costs (e.g., energy expenditure) and risk much greater costs (e.g., injury), both of which are presumably weighed against the potential benefits (e.g., refuge, food, or mates). Such costs and benefits directly impact their distribution, life history, and fitness, so an understanding of the role aggression plays is crucial to a complete understanding of a species’ ecological niche. The research presented here evaluates the degree to which aggression has ecological and life history consequences, using several species of co-occurring crabs as models in a combination of laboratory and field experiments. Specifically, we investigated: 1) how conspecific aggressive interactions compare across several ecologically overlapping crab species, 2) the impact exposure to aggression during the juvenile life phase has on the growth, maturity, injury, and survival rates of decapod crustaceans, 3) whether both intra- and interspecific aggression and competition among co-occurring crab species alter habitat selection and play a role in the success of invasive species, and 4) if injury patterns, spatial distribution, and habitat selection across the intertidal zone can be correlated to aggression. ^ In Chapter One, we present a comparative analysis of the degree to which different species of crabs engage in aggressive behavior. We focused on six species of co-occurring New England crabs, including the invasive Hemigrapsus sanguineus and Carcinus maenas, and the native Cancer irroratus, Dyspanopeus sayi, Libinia emarginata, and Ovalipes ocellatus. ^ We then studied the costs of aggressive behavior in Chapter Two, focusing particularly on the impact agonism has on growth, maturity, injury, and survival. We selected juvenile Hemigrapsus sanguineus, Carcinus maenas, and Cancer irroratus crabs, three species that directly co-occur and display comparable levels of aggression. ^ Hemigrapsus sanguineus, one of the species used in all four experiments presented in this dissertation, is a highly successful invasive species whose success stems partly from its ability to exclude established crab species from preferred rocky and cobble intertidal habitat. In Chapter Three, we assessed preference and competition for habitat types (cobble vs. sand) for H. sanguineus and two competitor species; the previously established invasive green crab, Carcinus maenas, and the native rock crab, Cancer irroratus, in New England. ^ One outcome of aggression is often injury, and these intertidal crab species exhibit high occurrences of both claw and leg loss. However, while it is difficult to ascertain the cause of such injuries, the impact on the distribution and demography of injured individuals across habitat types is relatively easy to assess. We found little evidence for differences in the distribution of injured H. sanguineus (the sole common species found in surveys) across intertidal zones, with half of all crabs exhibiting loss of at least one limb. Injury also correlated with age and reproductive status which, in turn, did effect distribution. ^ The results of this series of studies underscore the impact of aggression (and related competition) on shaping many aspects of a species’ ecology. Though the outcome of aggressive behavior is not always easy to ascertain, the overall results of our research serve to further illuminate our understanding of community ecology, invasion biology, life history and fitness, and ethology in general. (Abstract shortened by ProQuest.)^
Niels-Viggo Schou Hobbs,
"Agonistic behavior and costs of aggression in decapod crustaceans"
Dissertations and Master's Theses (Campus Access).