Territory acquisition mediates the influence of predators and climate on juvenile red squirrel survival

Juvenile survival to first breeding is a key life history stage. Survival through this period can be particularly challenging when it coincides with harsh environmental conditions like winter climate or food scarcity, and so cohort survival can be highly variable. However, the small size and dispersive nature of juveniles makes studying their survival difficult. In territorial species, a key life history event is the acquisition of a territory. A territory is expected to enhance survival, but how it does so, possibly through mediating mortality, is not often identified. We tested how the timing of territory acquisition influenced the survival of juvenile North American red squirrels Tamiasciurus hudsonicus, hereafter red squirrels, and how the timing of this event mediated sources of mortality. We hypothesized that securing a territory prior to the caching season would reduce juvenile susceptibility to predation or climatic factors over winter. Using 27 years of data on the survival of individually-marked juvenile red squirrels, we tested how the timing of territory acquisition influenced survival, whether the population density of red squirrel predators and mean temperature over winter were related to individual survival probability, and if territory ownership mediated these effects. Juvenile survival was lower in years of high predator abundance and in colder winters. Autumn territory owners were less susceptible to lynx Lynx canadensis, and possibly mustelid Mustela and Martes spp., predation. Autumn territory owners had lower survival in colder winters, while non-owners had higher survival in cold winters. Our results show how the timing of a life history event like territory acquisition can directly affect survival and also mediate the effects of biotic and abiotic factors later in life. This engenders a better understanding of the fitness consequences of the timing of key life history events.

Uncharted Territories: Defense of Space in Crustacea

Territoriality is a special case of resource defense, in which space is actively defended for exclusive use. As active defense is likely to be costly, territoriality is expected only when the benefits of exclusivity outweigh these costs. In most territorial species of noncrustacean taxa, the defended space includes resources critical for reproduction or food. These resources are not only critical for reproductive success, but also are vulnerable to “looting”, that is, the value of these resources may be reduced through short-term intrusions, even without loss of ownership, thus providing an advantage for active defense of exclusive space. Many crustaceans defend space, particularly burrows or other shelters that are refuges from predation or environmental stressors. While protection is obviously a critical resource, it is not a resource that necessarily requires exclusivity; indeed, many crustaceans that depend upon shelters for protection do not defend them for exclusive use. Nonetheless, many crustacean taxa aggressively defend exclusive access to their shelters. Crustaceans, then, may be especially suitable for testing alternative hypotheses of territoriality, including the potential benefits of interindividual spacing rather than defense of space per se. It is also worth considering a null hypothesis for territoriality: aggressive defense of space in crustaceans may be an artifact of relatively sedentary species with high intraspecific aggression favored in other contexts, rather than aggression favored for defense of particular resources. In addition to these questions, much remains to be learned about territorial behaviors in crustaceans. Most notably, the boundaries of defended space are unknown in many taxa. Understanding the boundaries of defended space is important for understanding the ecological consequences of territoriality, as well as aspects of territory acquisition and the roles of neighbor relationships and territorial advertisement signals in territory defense. Many crustacean territories appear to differ from those described for other animals, especially terrestrial species; it is not clear, however, whether these differences are due to differences in function or habitat, or rather result from our incomplete knowledge of crustacean territoriality.

Repertoire structure, song sharing, reproductive success, and territory tenure in a population of Canada Warblers (Cardellina canadensis) in central New Hampshire

Sexual selection for larger repertoires and the social advantages of sharing songs with territorial neighbours are two forces that may drive the evolution of complex song repertoires in songbirds. To evaluate the influence of these two selective pressures on repertoire evolution in a species with a complex repertoire, we examined repertoire structure, song sharing, reproductive success, and territory tenure in a Canada Warbler (Cardellina canadensis (L., 1766)) population in New Hampshire. Over two breeding seasons, we recorded 63 singing males, classified their song repertoires, quantified male song sharing, and determined male reproductive success and territory tenure. Male Canada Warblers had complex repertoires averaging 12 phrases (particular sequences of song elements) and 55 variants (songs composed of particular sequences of phrases). Song sharing decreased significantly with distance between territories, all of which were <1.75 km apart. Network analysis revealed clusters of male neighbours with high variant sharing, which was significantly associated with longer territory tenure. Overall pairing and fledging success were high, but were not related to repertoire size or song sharing. Our results suggest that song sharing aids in male territory acquisition and defence, and that females may therefore select mates based on their ability to retain a high-quality territory.

Niche partitioning along the diet axis in a colour polymorphic population of Eastern Red-backed Salamanders, Plethodon cinereus

Eastern Red-backed Salamanders are colour polymorphic and have become a model system for examining ecological separation and the mechanisms for potential divergence in sympatry. Morphs of this species are differentiated along several niche axes including temperature optima, territorial behaviour, and response to predators. We were interested in whether temporal variation in ecological conditions would affect foraging behavior and ultimately diet. The goal of our study was to compare the diets of striped and unstripedP. cinereusover a range of seasonal conditions to better understand if the reported differences observed in the fall season at our field site remain consistent through the active season of this species. Diet differences between the two morphs were greatest during spring and fall when salamanders are most abundant at the surface. These diet differences were driven largely by two prey categories. In the spring, striped salamanders ate more oribatid mites and in the fall they consumed more entomobryomorph Collembola. Trade-offs associated with territory acquisition coupled with physiological and morphological differences may explain the observed seasonal niche partitioning related to the diet in this population.

The Policy-Driven Political Style of James K. Polk

This chapter assesses the strengths and weaknesses of James K. Polk, focusing on six realms: public communication, organizational capacity, political skill, policy vision, cognitive style, and emotional intelligence. Polk, has been called the only strong chief executive between Andrew Jackson and Abraham Lincoln. Polk also ranks near the top in the perennial polls on greatness in the White House. On the day of his inauguration, Polk declared that his administration would advance “four great measures”: division with Great Britain of the jointly administered Oregon Territory, acquisition of California, tariff reduction, and passage of a measure requiring the government to keep its funds in its own vaults instead of in state and private banks. Polk accomplished all this and more in a single four-year term. Despite his accomplishments, Polk lacked foresight. This was particularly evident in his inability to foresee that his territorial acquisitions would trigger a spiral of controversy that was to come to a head in the Civil War.