Plant-hummingbird pollination networks exhibit limited rewiring after experimental removal of a locally abundant plant species.

Mutualistic relationships, such as those between plants and pollinators, may be vulnerable to the local extinctions predicted under global environmental change. However, network theory predicts that plant-pollinator networks can withstand species loss if pollinators switch to alternative floral resources (rewiring). Whether rewiring occurs following species loss in natural communities is poorly known because replicated species exclusions are difficult to implement at appropriate spatial scales. We experimentally removed a hummingbird-pollinated plant, Heliconia tortuosa, from within tropical forest fragments to investigate how hummingbirds respond to temporary loss of an abundant resource. Under the rewiring hypothesis, we expected that behavioural flexibility would allow hummingbirds to use alternative resources, leading to decreased ecological specialization and reorganization of the network structure (i.e. pairwise interactions). Alternatively, morphological or behavioural constraints-such as trait-matching or interspecific competition-might limit the extent to which hummingbirds alter their foraging behaviour. We employed a replicated Before-After-Control-Impact experimental design and quantified plant-hummingbird interactions using two parallel sampling methods: pollen collected from individual hummingbirds ('pollen networks', created from >300 pollen samples) and observations of hummingbirds visiting focal plants ('camera networks', created from >19,000 observation hours). To assess the extent of rewiring, we quantified ecological specialization at the individual, species and network levels and examined interaction turnover (i.e. gain/loss of pairwise interactions). H. tortuosa removal caused some reorganization of pairwise interactions but did not prompt large changes in specialization, despite the large magnitude of our manipulation (on average, >100 inflorescences removed in exclusion areas of >1 ha). Although some individual hummingbirds sampled through time showed modest increases in niche breadth following Heliconia removal (relative to birds that did not experience resource loss), these changes were not reflected in species- and network-level specialization metrics. Our results suggest that, at least over short time-scales, animals may not necessarily shift to alternative resources after losing an abundant food resource-even in species thought to be highly opportunistic foragers, such as hummingbirds. Given that rewiring contributes to theoretical predictions of network stability, future studies should investigate why pollinators might not expand their diets after a local resource extinction.

The evolution, ecology, and conservation of hummingbirds and their interactions with flowering plants.

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 stressors - such as habitat loss and fragmentation, climate change, and introduction of non-native plants - may interact to affect hummingbirds and the plants they pollinate.

When are hypotheses useful in ecology and evolution?

Research hypotheses have been a cornerstone of science since before Galileo. Many have argued that hypotheses (1) encourage discovery of mechanisms, and (2) reduce bias-both features that should increase transferability and reproducibility. However, we are entering a new era of big data and highly predictive models where some argue the hypothesis is outmoded. We hypothesized that hypothesis use has declined in ecology and evolution since the 1990s, given the substantial advancement of tools further facilitating descriptive, correlative research. Alternatively, hypothesis use may have become more frequent due to the strong recommendation by some journals and funding agencies that submissions have hypothesis statements. Using a detailed literature analysis (N = 268 articles), we found prevalence of hypotheses in eco-evo research is very low (6.7%-26%) and static from 1990-2015, a pattern mirrored in an extensive literature search (N = 302,558 articles). Our literature review also indicates that neither grant success nor citation rates were related to the inclusion of hypotheses, which may provide disincentive for hypothesis formulation. Here, we review common justifications for avoiding hypotheses and present new arguments based on benefits to the individual researcher. We argue that stating multiple alternative hypotheses increases research clarity and precision, and is more likely to address the mechanisms for observed patterns in nature. Although hypotheses are not always necessary, we expect their continued and increased use will help our fields move toward greater understanding, reproducibility, prediction, and effective conservation of nature.

Patterns of male dispersal in Verreaux's sifaka (Propithecus verreauxi) at Kirindy Mitea National Park.

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.