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Males of many group-living mammals emigrate from their social groups to improve mating opportunities. To help mitigate the social and locational costs of dispersal and to increase reproductive benefits, they may immigrate seasonally, immigrate alongside a partner, and/or replace the alpha male (versus entering a group as a subordinate). Verreaux's sifaka (Propithecus verreauxi) are highly seasonally breeding primates characterized by male-biased dispersal. We hypothesized that (i) males time immigrations to pursue immediate mating opportunities, (ii) entrances with partners more often result in alpha male replacement, and (iii) male competitive ability affects immigration strategy and alpha male tenure length. To assess these proximate aspects of male dispersal, we examined 7 years of demographic, morphological, and behavioral data for five social groups of Verreaux's sifaka in the Kirindy Mitea National Park in western Madagascar. Contrary to expectations and studies of sifaka dispersal in other populations, we detected no strong seasonal pattern in immigrations. Immigrations occurred individually and with partners, and a trend existed for partners to increase the likelihood of replacing an alpha male. Pronounced activity of the sternal scent gland (a proxy for testosterone and prior dominance status), but not body mass, canine size, or potential correlates of leaping ability, significantly influenced immigration strategy. The absence of a seasonal immigration pattern suggests that fluid group boundaries may allow mating success without establishment in a social group before the mating season. Our results also suggest that male immigration strategies are affected by age, prior dominance status, and testosterone levels but not morphological indicators of individual competitive ability. Coalitions may be used to improve competitive ability. Finally, differences in seasonal immigration patterns and length of alpha male vacancies observed at Kirindy Mitea may be due to the relatively low population density. Am. J. Primatol. 79:e22455, 2017. © 2015 Wiley Periodicals, Inc.

The ecological co-dependency between plants and hummingbirds is a classic example of a mutualistic interaction: hummingbirds rely on floral nectar to fuel their rapid metabolisms, and more than 7000 plant species rely on hummingbirds for pollination. However, threats to hummingbirds are mounting, with 10% of 366 species considered globally threatened and 60% in decline. Despite the important ecological implications of these population declines, no recent review has examined plant-hummingbird interactions in the wider context of their evolution, ecology, and conservation. To provide this overview, we (i) assess the extent to which plants and hummingbirds have coevolved over millions of years, (ii) examine the mechanisms underlying plant-hummingbird interaction frequencies and hummingbird specialization, (iii) explore the factors driving the decline of hummingbird populations, and (iv) map out directions for future research and conservation. We find that, despite close associations between plants and hummingbirds, acquiring evidence for coevolution (versus one-sided adaptation) is difficult because data on fitness outcomes for both partners are required. Thus, linking plant-hummingbird interactions to plant reproduction is not only a major avenue for future coevolutionary work, but also for studies of interaction networks, which rarely incorporate pollinator effectiveness. Nevertheless, over the past decade, a growing body of literature on plant-hummingbird networks suggests that hummingbirds form relationships with plants primarily based on overlapping phenologies and trait-matching between bill length and flower length. On the other hand, species-level specialization appears to depend primarily on local community context, such as hummingbird abundance and nectar availability. Finally, although hummingbirds are commonly viewed as resilient opportunists that thrive in brushy habitats, we find that range size and forest dependency are key predictors of hummingbird extinction risk. A critical direction for future research is to examine how potential stressorssuch as habitat loss and fragmentation, climate change, and introduction of non-native plantsmay interact to affect hummingbirds and the plants they pollinate.