Leone M. Brown

Taxonomic, phylogenetic, and trait Beta diversity in South American hummingbirds.

Comparison of the taxonomic, phylogenetic, and trait dimensions of beta diversity may uncover the mechanisms that generate and maintain biodiversity, such as geographic isolation, environmental filtering, and convergent adaptation. We developed an approach to predict the relationship between environmental and geographic distance and the dimensions of beta diversity. We tested these predictions using hummingbird assemblages in the northern Andes. We expected taxonomic beta diversity to result from recent geographic barriers limiting dispersal, and we found that cost distance, which includes barriers, was a better predictor than Euclidean distance. We expected phylogenetic beta diversity to result from historical connectivity and found that differences in elevation were the best predictors of phylogenetic beta diversity. We expected high trait beta diversity to result from local adaptation to differing environments and found that differences in elevation were correlated with trait beta diversity. When combining beta diversity dimensions, we observe that high beta diversity in all dimensions results from adaption to different environments between isolated assemblages. Comparisons with high taxonomic, low phylogenetic, and low trait beta diversity occurred among lowland assemblages separated by the Andes, suggesting that geographic barriers have recently isolated lineages in similar environments. We provide insight into mechanisms governing hummingbird biodiversity patterns and provide a framework that is broadly applicable to other taxonomic groups.

Increasing Group Size Alters Behavior of a Folivorous Primate

Group size influences many aspects of mammalian social life, including stress levels, disease transmission, reproductive rates, and behavior. However, much of what is known about the effects of group size on behavioral ecology has come from comparisons across multiple groups of different sizes. These findings may be biased because behavioral differences across groups may be more indicative of how environmental variation influences animal behavior, rather than group size itself. To partially circumvent this limitation, we used longitudinal data to examine how changes in group size across time affect the behavior of folivorous red colobus monkeys (Procolobus rufomitratus) of Kibale National Park, Uganda. Controlling for food availability, we demonstrated that increasing group size resulted in altered activity budgets, based on 6 yr of data on a group that increased from 57 to 98 members. Specifically, as group size increased, individuals spent less time feeding and socializing, more time traveling, and increased the diversity of their diet. These changes appear to allow the monkeys to compensate for greater scramble competition apparent at larger group sizes, as increasing group size did not show the predicted relationship with lower female fecundity. Our results support recent findings documenting feeding competition in folivorous primates. Our results also document behavioral flexibility, an important trait that allows many social mammals to maximize the benefits of sociality (e.g., increased vigilance), while minimizing the costs (e.g., increased feeding competition).

Demography, traits and vulnerability to urbanization: can we make generalizations?

Summary 1. Human-induced land cover change threatens species diversity and ecosystem services. The rapid pace of current change makes predicting species’ declines imperative, but leaves little time for thorough study of all species. One solution is to make generalizations about species’ vulnerability to urbanization based on traits common among studied species in decline. 2. To date, most generalizations about traits associated with species’ declines in response to urbanization are based on presence or abundance, or detailed studies of a few species. If these generalizations broadly reflect responses to urbanization, they should hold across the mechanisms driving patterns of abundance, such as survival or reproduction. 3. Across 68 bird species in the north-eastern USA, we investigated how food preference, nest location, habitat preference, migration distance, number of broods, clutch size, body mass and an interaction between urbanization and these traits affected survival and reproduction. 4. Mass was the strongest predictor of survival, followed by number of broods, migration distance and nest location. Nest location was the strongest predictor of reproduction, followed by migration distance. No interaction between urbanization and species’ traits affected survival; however, differences in response to urbanization among species with different food preferences, migration distances, masses, nest locations and number of broods were important in predicting reproduction. 5. Synthesis and applications. We found that some traits influenced demographic rates even though they were not associated with urbanization; identifying differences in species’ baseline demographic rates, irrespective of urbanization, is needed to guide management objectives. Reproduction, but not survival, was influenced by urbanization, suggesting that management in our region of study should target increasing suitable nest sites and reducing nest predation. Determining traits associated with demographic rates and urbanization across broad geographic extents can provide new insights for species’ management and help guide conservation initiatives.

Losing a battle but winning the war: moving past preference–performance to understand native herbivore–novel host plant interactions

Introduced plants can positively affect population viability by augmenting the diet of native herbivores, but can negatively affect populations if they are subpar or toxic resources. In organisms with complex life histories, such as insects specializing on host plants, the impacts of a novel host may differ across life stages, with divergent effects on population persistence. Most research on effects of novel hosts has focused on adult oviposition preference and larval performance, but adult preference may not optimize offspring performance, nor be indicative of host quality from a demographic perspective. We compared population growth rates of the Baltimore checkerspot butterfly, Euphydryas phaeton, on an introduced host, Plantago lanceolata (English plantain), and the native host Chelone glabra (white turtlehead). Contrary to the previous findings suggesting that P. lanceolata could be a population sink, we found higher population growth rates (λ) on the introduced than the native host, even though some component parameters of λ were higher on the native host. Our findings illustrate the importance of moving beyond preference–performance studies to integrate vital rates across all life stages for evaluating herbivore–host plant relationships. Single measures of preference or performance are not sufficient proxies for overall host quality nor do they provide insights into longer term consequences of novel host plant use. In our system, in particular, P. lanceolata may buffer checkerspot populations when the native host is limiting, but high growth rates could lead to crashes over longer time scales.

Using animal movement behavior to categorize land cover and predict consequences for connectivity and patch residence times

ContextLandscape-scale population dynamics are driven in part by movement within and dispersal among habitat patches. Predicting these processes requires information about how movement behavior varies among land cover types.ObjectivesWe investigated how butterfly movement in a heterogeneous landscape varies within and between habitat and matrix land cover types, and the implications of these differences for within-patch residence times and among-patch connectivity.MethodsWe empirically measured movement behavior in the Baltimore checkerspot butterfly (Euphydryas phaeton) in three land cover classes that broadly constitute habitat and two classes that constitute matrix. We also measured habitat preference at boundaries. We predicted patch residence times and interpatch dispersal using movement parameters estimated separately for each habitat and matrix land cover subclass (5 categories), or for combined habitat and combined matrix land cover classes (2 categories). We evaluated the effects of including edge behavior on all metrics.ResultsOverall, movement was slower within habitat land cover types, and faster in matrix cover types. Butterflies at forest edges were biased to remain in open areas, and connectivity and patch residence times were most affected by behavior at structural edges. Differences in movement between matrix subclasses had a greater effect on predictions about connectivity than differences between habitat subclasses. Differences in movement among habitat subclasses had a greater effect on residence times.ConclusionsOur findings highlight the importance of careful classification of movement and land cover in heterogeneous landscapes, and reveal how subtle differences in behavioral responses to land cover can affect landscape-scale outcomes.

Consequences of resource supplementation for disease risk in a partially migratory population

Anthropogenic landscape features such as urban parks and gardens, landfills and farmlands can provide novel, seasonally reliable food sources that impact wildlife ecology and distributions. In historically migratory species, food subsidies can cause individuals to forgo migration and form partially migratory or entirely sedentary populations, eroding a crucial benefit of migration: pathogen avoidance through seasonal abandonment of transmission sites and mortality of infected individuals during migration. Since many migratory taxa are declining, and wildlife populations in urban areas can harbour zoonotic pathogens, understanding the mechanisms by which anthropogenic resource subsidies influence infection dynamics and the persistence of migration is important for wildlife conservation and public health. We developed a mathematical model for a partially migratory population and a vector-borne pathogen transmitted at a shared breeding ground, where food subsidies increase the nonbreeding survival of residents. We found that higher resident nonbreeding survival increased infection prevalence in residents and migrants, and lowered the fraction of the population that migrated. The persistence of migration may be especially threatened if residency permits emergence of more virulent pathogens, if resource subsidies reduce costs of infection for residents, and if infection reduces individual migratory propensity. This article is part of the theme issue ‘Anthropogenic resource subsidies and host–parasite dynamics in wildlife’.

Molting while breeding? Lessons from New World Tyrannus Flycatchers

Abstract Songbirds must annually undergo two energetically demanding but important activities: breeding and feather molt. Due to the high energetic investment that each demands, these two events are generally not carried out simultaneously. However, substantial variation in the level of annual reproductive investment among populations may result in variation in molt-breeding overlap between them. With the goal of understanding whether different songbird populations overlap molt and breeding, and, if so, to determine directions for research on the potential tradeoffs involved, we describe the relationship between clutch size, molt, and energetic condition within a genus of New World Flycatchers (Tyrannus). Of 219 Flycatchers sampled, only one individual molted flight feathers while breeding, suggesting that molting flight feathers and breeding simultaneously is too energetically expensive at any clutch size. However, some Flycatchers molted body feathers during the breeding season. When we tested for an effect of clutch size, sex and energetic condition on body molt intensity during the breeding season, only clutch size and sex had significant effects, with a negative effect of clutch size on body molt intensity in males but not in females. Based on these results, we develop a set of hypotheses to guide future studies on the potential tradeoffs between investment in reproduction and molt.ZusammenfassungMauser während der Brutzeit? Was machen die neuweltlichenTyrannusFliegenschnäpper? Singvögel müssen zweimal im Jahr energetisch aufwändige, aber wichtige Prozesse durchlaufen: Brutzeit und Mauser. Da beide Aktivitäten hohe energetische Investitionen erfordern, laufen sie üblicherweise nicht gleichzeitig ab. Aber größere Unterschiede zwischen einzelnen Populationen in den jährlichen Fortpflanzungsinvestitionen haben möglicherweise Überlappungen von Mauser mit Brutzeit zur Folge. Ziel unserer Untersuchung war es, besser zu verstehen, ob und wie sehr sich Mauser und Brutzeit bei unterschiedlichen Singvogel-Populationen überschneiden, und festzuhalten, in welche Richtung zukünftige Untersuchungen der möglichen Vor- und Nachteile (tradeoffs) gehen sollten. Hierfür beschreiben wir für eine Gattung von Fliegenschnäppern (Tyrannus) aus der Neuen Welt die Zusammenhänge zwischen Gelegegröße, Mauser und energetischem Zustand. Von den 219 untersuchten Fliegenschnäppern zeigte nur ein einziges Tier whärend der Brutzeit auch Mauser an den Schwungfedern, was nahelegt, dass unabhängig von der Gelegegröße die Mauser der Schwungfedern und gleichzeitiges Brüten energetisch zu teuer ist. Dessen ungeachtet mauserten einige Fliegenschnäpper während der Brutzeit ihr Körpergefieder. Als wir untersuchten, ob es mögliche Auswirkungen der Gelegegröße, der sexuellen Aktivitäten und des energetischen Zustands der Vögel auf die Intensität ihrer Mauser während der Brutzeit gibt, zeigten nur die Gelegegröße und sexuellen Aktivitäten einen signifikanten Effekt; es gab einen negativen Effekt der Gelegegröße auf die Intensität der Mauser des Körpergefieders bei Männchen, nicht aber bei Weibchen. Auf der Basis dieser Befunde stellen wir eine Reihe von Hypothesen auf als Anregung für zukünftige Untersuchungen des potentiellen tradeoffs zwischen der Investition in Fortpflanzung und Mauser.

Does movement behaviour predict population densities? A test with 25 butterfly species

Diffusion, which approximates a correlated random walk, has been used by ecologists to describe movement, and forms the basis for many theoretical models. However, it is often criticized as too simple a model to describe animal movement in real populations. We test a key prediction of diffusion models, namely, that animals should be more abundant in land cover classes through which they move more slowly. This relationship between density and diffusion has rarely been tested across multiple species within a given landscape. We estimated diffusion rates and corresponding densities of 25 Israeli butterfly species from flight path data and visual surveys. The data were collected across 19 sites in heterogeneous landscapes with four land cover classes: semi-natural habitat, olive groves, wheat fields and field margins. As expected from theory, species tended to have higher densities in land cover classes through which they moved more slowly and lower densities in land cover classes through which they moved more quickly. Two components of movement (move length and turning angle) were not associated with density, nor was expected net squared displacement. Move time, however, was associated with density, and animals spent more time per move step in areas with higher density. The broad association we document between movement behaviour and density suggests that diffusion is a good first approximation of movement in butterflies. Moreover, our analyses demonstrate that dispersal is not a species-invariant trait, but rather one that depends on landscape context. Thus, land cover classes with high diffusion rates are likely to have low densities and be effective conduits for movement.

On the relationship between body condition and parasite infection in wildlife: a review and meta‐analysis

Body condition metrics are widely used to infer animal health and to assess costs of parasite infection. Since parasites harm their hosts, ecologists might expect negative relationships between infection and condition in wildlife, but this assumption is challenged by studies showing positive or null condition-infection relationships. Here, we outline common condition metrics used by ecologists in studies of parasitism, and consider mechanisms that cause negative, positive, and null condition-infection relationships in wildlife systems. We then perform a meta-analysis of 553 condition-infection relationships from 187 peer-reviewed studies of animal hosts, analysing observational and experimental records separately, and noting whether authors measured binary infection status or intensity. Our analysis finds substantial heterogeneity in the strength and direction of condition-infection relationships, a small, negative average effect size that is stronger in experimental studies, and evidence for publication bias towards negative relationships. The strongest predictors of variation in study outcomes are host thermoregulation and the methods used to evaluate body condition. We recommend that studies aiming to assess parasite impacts on body condition should consider host-parasite biology, choose condition measures that can change during the course of infection, and employ longitudinal surveys or manipulate infection status when feasible.