James W. A. Grant

Threats to Endangered Species in Canada

ABSTRACT We quantified the threats facing 488 species in Canada, categorized by COSEWIC (Committee on the Status of Endangered Wildlife in Canada) as extinct, extirpated, endangered, threatened, or of special concern. Habitat loss is the most prevalent threat (84%), followed by overexploitation (32%), native species interactions (31%), natural causes (27%), pollution (26%), and introduced species (22%). Agriculture (46%) and urbanization (44%) are the most common human activities causing habitat loss and pollution. For extant species, the number of threats per species increases with the level of endangerment. The prevalence of threat types varies among major habitats, with overexploitation being particularly important, and introduced species particularly unimportant, for marine species. Introduced species are a much less important threat in Canada than in the United States, but the causes of endangerment are broadly similar for Canadian and globally endangered species.

Operational sex ratio, mediated by synchrony of female arrival, alters the variance of male mating success in Japanese medaka

Abstract The hypotheses that variation in male mating success and use of aggression by competing males increase with decreasing synchrony of female arrival were experimentally tested. Groups of three male Japanese medaka, Oryzias latipes (Pisces, Oryziidae) were allowed to compete for females that were placed in the tank either simultaneously (synchronous treatment, male-to-female operational sex ratio=0·5) or sequentially (asynchronous treatment, operational sex ratio=3). In these experiments, the mating system of medaka was scramble-competition polygyny because male mating success was primarily determined by their persistence in following and courting females rather than by dominance and aggression. As predicted, the coefficient of variation of male mating success and the rate of aggression by males was higher in the asynchronous than in the synchronous treatment. In addition, the percentage of matings in which a sneaker participated was also higher in the asynchronous than in the synchronous treatment. Operational sex ratio, mediated by female synchrony, seems to be an important proximate factor influencing the intensity of male-male competition. These results suggest that differences between males in their ability to scramble for females can generate important variance in mating success, a mechanism that is often overlooked in the literature on mating systems.

OPTIMAL TERRITORY SIZE IN THE CONVICT CICHLID

Models of optimal territory size are usually tested only by demonstrating that territory size is inversely related to food abundance or intruder number. The most fundamental predictions of the models, however, have rarely been tested: i.e. the fitness of the defender is a function of territory size and the optimal territory is one of intermediate size. We tested these predictions by measuring the growth rate of large convict cichlids (Archocentrus nigrofasciatus, formerly Cichlasoma nigrofasciatum) while defending food patches against smaller intruders over a 10-day period. Food patches differed in area by more than two orders of magnitude. We manipulated food abundance so that it increased with patch size in a decelerating way. As assumed, the realized benefits of defence (weight of food eaten by the defender) and the costs of defence (chase rate and chase radius) both increased in a decelerating way with increasing patch area. As predicted, the growth rate of the defender first increased and then decreased with increasing patch size. The initial increase in defender growth rate with increasing patch size was related to an increase in food eaten, but the decrease in growth rate for fish defending the largest patches was related to the costs of defence. Fish defending large patches had a low growth efficiency, apparently because of the social stress caused by intruders in their territories. Taken together, these results support the assumptions and predictions of optimal territory size models.

Distraction sneakers decrease the expected level of aggression within groups: a game-theoretic model.

Hawk‐dove games have been extensively used to predict the conditions under which group‐living animals should defend their resources against potential usurpers. Typically, game‐theoretic models on aggression consider that resource defense may entail energetic and injury costs. However, intruders may also take advantage of owners who are busy fighting to sneak access to unguarded resources, imposing thereby an additional cost on the use of the escalated hawk strategy. In this article we modify the two‐strategy hawk‐dove game into a three‐strategy hawk‐dove‐sneaker game that incorporates a distraction‐sneaking tactic, allowing us to explore its consequences on the expected level of aggression within groups. Our model predicts a lower proportion of hawks and hence lower frequencies of aggressive interactions within groups than do previous two‐strategy hawk‐dove games. The extent to which distraction sneakers decrease the frequency of aggression within groups, however, depends on whether they search only for opportunities to join resources uncovered by other group members or for both unchallenged resources and opportunities to usurp.

Diel activity patterns of the fish community in a temperate stream

The diel activity patterns of fishes in a temperate New Brunswick stream were studied during the summer over 5 years. Young-of-the year Atlantic salmon Salmo salar and blacknose dace Rhinichthys atratulus were more active during the day than at night, whereas lake chub Couesius plumbeus, brook trout Salvelinus fontinalis and adult white suckers Catostomus commersonii were more active at night than during the day. Because fishes were as likely to be nocturnal as diurnal, the data suggest that more night-time sampling is needed to provide an unbiased view of fish community structure in temperate streams.