Doctor of Philosophy in Zoology (PhD)
Paramo bird communities: Understanding a poorly known Andean ecosystem under increasing risk of extinction
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Current thinking suggests that survival, and consequently lifespan of organisms, can be understood in terms of trade-offs between self-maintenance and reproduction, and constraints imposed by physiological mechanisms, such as metabolic intensity. While comparative studies show that many life history traits covary predictably with climate, few studies have examined variation in survival across latitudinal or elevational gradients. I paired survival rates with reproductive, morphological, behavioral, and physiological traits, as well as environmental variables to quantify the intrinsic and extrinsic drivers shaping avian life histories. In Chapter 2 I ask whether tropical birds around the world are longer lived than their temperate counterparts. My results suggested an inverse relationship between latitude and survival in the northern hemisphere, but this pattern is dampened or absent for the majority of southern hemisphere species. I also showed that extrinsic factors related to climate were poor predictors of survival compared to latitude alone, and that the relationship between survival and latitude is strongly mediated by intrinsic traits ― larger, non-migratory species with smaller clutch size had the highest survival. In Chapter 3 I focus within the Neotropics to examine how a basic physiological trait (basal metabolic rate; BMR) is linked to survival of montane and lowland birds. I found that lower BMR predicted higher survival, regardless of the elevation at which species occurred. In addition, elevation had a direct negative effect on survival, perhaps due to harsher abiotic conditions, low site fidelity, or both at higher elevations. To help facilitate estimates of age-specific survival in future studies, I determined the molt ageing criteria for South American manakin species in Chapter 4, which can be used to distinguish juveniles from adults. Like many temperate species, the occurrence of a partial preformative molt allowed separation of age classes based on the presence of molt limits. By drawing on both variation within the tropics and across birds globally, this dissertation provides new evidence of the connections between the high survival rate of tropical birds, their life history traits, and the environment.
Human disturbances threaten tropical forests, potentially disrupting plant-animal interactions. Though many studies have assessed the effects of habitat disturbance on either plants or animals, we have a limited understanding of how disrupted interactions will affect both groups of interacting species and whether impacts vary with spatial scale. This hinders our ability to predict how logging, a widespread threat to tropical forests, affects plant and animal communities, particularly in combination with overhunting, a common co-occurring threat. I excluded small to large-bodied mammals from research plots in logged and unlogged forests in Borneo to quantify the effects of logging and hunting on seed predation and establishment in five dominant tree species (Chapter 2). Granivore-induced seed mortality was higher in logged forest. Defaunation did not affect seed mortality. Seedling establishment was highest when small to large-bodied mammals were excluded in logged forest, suggesting that the effects of logging and hunting interact to alter seedling recruitment. I used the same animal exclusion plots to assess impacts on diversity and the distribution of morphological traits in tagged seedling communities over four years (Chapter 3). Excluding small to large vertebrates did not affect overall seedling diversity but animals disproportionately killed seedlings from large-fruited genera in logged forest, reducing community fruit size. Animals altered plant traits, though impacts may be underestimated by focusing only on changes to taxonomic diversity. Selective logging can also intensify the patchiness of food availability across the landscape. Spatiotemporal variability in food abundance is especially pronounced during mast fruiting events, yet the consequences for animal habitat use at different spatial scales in faunally intact systems is unclear. I used camera traps to estimate the site use of several vertebrate species across two dipterocarp mast years and a non-mast year at large and small spatial scales (Chapter 4). Site use was positively associated with masting for several taxa, though strong response were mostly limited to intact forest. Even key consumers (bearded pigs) showed reduced responses in the logged forest at the small scale. Overall, my work demonstrates that anthropogenic disturbances disrupt plant-animal interactions by altering plant recruitment and limiting vertebrate responses to resource availability.
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Cospeciation is when two species share similar or identical phylogenies as a result of their interactions and is often predicted with ectosymbionts, organisms that complete the majority of their lifecycle on a host. When an organism is dependent on another to complete it’s reproductive cycle, there is potential for cospeciation. Due to limited dispersal capabilities beyond contact between a current and potential host species, many ectosymbionts have phylogenies that mirror their hosts’. In this thesis, I test this prediction using Myrsidea feather lice found on Neotropical Mionectes flycatchers from Manu National Park, Peru. My results show strong evidence of cospeciation by comparing trees built using sequences from the Myrsidea’s mitochondrial (CO1) and nuclear (EF-1α) genes to previously described host trees from Miller et al. (2008) and Jetz et al. (2012). These findings agree with previous morphological descriptions of two Myrsidea lice species co-occurring with Mionectes hosts and provides evidence that there are currently two previously undescribed species of Myrsidea. This adds to our knowledge and understanding of how ectosymbionts and hosts interact through evolutionary time, and provides the basis for future studies on the description of Myrsidea which is an under-described group of widespread organisms.
The high species richness of antbirds (Thamnophilidae) in Amazonian lowlands, where as many as 40 species may coexist at local scales, represents a major challenge for ecologists to explain patterns of coexistence and niche evolution. I studied the foraging ecology of a local community of antbirds in a 2-Km² area of lowland forest in SE Peru to examine how co-occurring antbird species differ in their use of foraging resources, and whether these differences result in niche partitioning at the community level. I also examined whether resource use similarity was related to phylogenetic similarity in this local assemblage. Forty-four species of antbirds were detected in the study plot in a four-year period, with 30 species categorized as the local assemblage of common resident breeders. Multivariate analysis of foraging parameters showed that segregation at two height layers in two types of forest was more important than foraging substrates and maneuvers in explaining the differences observed in foraging behavior. However, a null model analysis revealed that at the community level, antbirds exhibited high foraging niche overlap, with average observed overlap significantly larger than expected by chance, indicating that antbirds prefer, rather than avoid, resources used by other species. No general relationship exists between phylogenetic similarity and niche overlap. Closely related species consistently exhibit high values of niche overlap, but some distantly related species also exhibit high niche similarity. Taken together, these results suggest that foraging niche similarity is the predominant pattern among co-occurring antbirds, and that positive interactions might explain the stable coexistence of species that use similar resources and habitats at a local scale.
Understanding the influence of species interactions on community structure is a long-standing goal in ecology. While many studies have focused on negative biotic interactions, the role of other mechanisms has received less attention, in particular, facilitation. In birds, a striking case of facilitation occurs in mixed-species flocks, in which individuals of different species move and forage as a group to obtain benefits from the association. These associations of species in mixed flocks have been described in different habitats during the last century; however, there is still much debate regarding the prevalence of this foraging strategy and the role it plays in Neotropical bird communities. In this study, I integrated data from mixed species flocks observations and species occurrence to investigate how facilitative interactions influence the structure of Neotropical bird communities across a 3000-m elevational gradient on the eastern slope of the Andes in Peru. First, I examine how the structure of mixed flocks changes across elevations. Second, I quantify the stability of these multispecies groups over time. Third, I evaluate the association of several key habitat variables with flock diversity. Finally, utilizing a dataset for the entire forest bird community, I assess the prevalence and importance of mixed-species flocks across the gradient. The results showed that flocks were highly organized and stable across elevations. Flocks across the gradient exhibited a similar general structure, composed of a stable core group of species and a more dynamic component of attending species. This spatial and temporal analysis suggests that the stability of mixed-species flocks in the Andes is similar to what has been previously described in the Amazonian lowlands, with flocks exhibiting stable home ranges and core member composition over time. Vegetation structure explained 63% of variation in flock richness along the gradient, with number of trees and canopy height as primary predictors. Importantly, this study demonstrates that mixed-species flocks are used by more than a third of bird species present in the community, suggesting that these facilitative interactions are an important and underappreciated component of tropical bird communities.
Small-bodied bird species exhibiting single-sex incubation must expend energy to create a buffered thermal environment for their eggs, while also meeting their own energetic requirements. The resultant trade-off between incubation and foraging is intensified in cold environments like the alpine, where energetic constraints are high. Ambient temperature influences incubation behaviour, with variable relationships across species, habitats and populations. I examined incubation rhythms of an alpine population of Horned Larks (Eremophila alpestris) in British Columbia across four years with different thermal regimes (2005 = moderate, 2006 = warm, 2010 = cold overnight, 2011 = cold during day) to determine whether incubating larks exhibited variable relationships between attentivity and temperature under different thermal conditions and how this related to management of the parent-offspring trade-off. Early in the morning, females had to leave their nest to forage to reduce their energy deficit following 7 h of night incubation in near freezing conditions. Since temperatures at this time were still