Browsing by Author "Lloyd, Penn"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Open Access
    Determinants and consequences of territory quality in the Bar-throated Apalis Apalis thoracica
    (2011) Chaskda, Adams Adamanyiwa; Hockey, Phil A R; Lloyd, Penn
    The underlying principles of territoriality propose that competition for resources compels individuals to defend areas (territories) that give them exclusive access to critical resources. The theory suggests that only high-quality individuals succeed in occupying areas rich in these resources with consequent benefits in terms of higher reproductive success and/or chances of survival. The main aims of this study were: i) to determine the ecological factors influencing variation in territory size and quality among Bar-throated Apalises Apalis thoracica; ii) to investigate the consequences of these factors for reproductive effort and reward, pair stability and survival; and iii) to investigate the signalling properties of the species' black breast band (a prominent 'badge' emblazoned across the white underparts) in relation to both male and territory quality.
  • Thumbnail Image
    Item
    Open Access
    Ecological and evolutionary processes in two southern African endemic birds
    (2011) Ribeiro, Angela M; Hockey, Phil A R; Lloyd, Penn
    In this dissertation, I propose a population-level framework that integrates ecology and population genetics to rethink the mechanisms that promote divergence. To accomplish that I studied two southern African endemic Cercotrichas scrub-robins: C. coryphaeus and C. signata. Despite its phylogenetic proximity the two study species occupy the two ends of the habitat spectrum available in southern Africa: semi-arid Karoo vs. Forest.
  • Thumbnail Image
    Item
    Open Access
    The ecological and geographic context of morphological and genetic divergence in an understorey-dwelling bird
    (Public Library of Science, 2014) Ribeiro, Angela M; Lloyd, Penn; Dean, W Richard J; Brown, Mark; Bowie, Rauri C K
    Advances in understanding the process of species formation require an integrated perspective that includes the evaluation of spatial, ecological and genetic components. One approach is to focus on multiple stages of divergence within the same species. Species that comprise phenotypically different populations segregated in apparently distinct habitats, in which range is presently continuous but was putatively geographically isolated provide an interesting system to study the mechanisms of population divergence. Here, we attempt to elucidate the role of ecology and geography in explaining observed morphological and genetic variation in an understorey-dwelling bird endemic to southeastern Africa, where two subspecies are recognized according to phenotype and habitat affinity. We carried out a range-wide analysis of climatic requirements, morphological and genetic variation across southeast Africa to test the hypothesis that the extent of gene flow among populations of the brown scrub-robin are influenced by their distinct climatic niches. We recovered two distinct trends depending on whether our analyses were hierarchically structured at the subspecies or at the within subspecies level. Between subspecies we found pronounced morphological differentiation associated with strong reproductive isolation (no gene flow) between populations occupying divergent climatic niches characterized by changes in the temperature of the warmest and wettest month. In contrast, within subspecies, we recovered continuous morphological variation with extensive gene flow among populations inhabiting the temperate and sub-tropical forests of southern Africa, despite divergence along the climate axis that is mainly determined by minimum temperature and precipitation of the coldest months. Our results highlight the role of niche divergence as a diversifying force that can promote reproductive isolation in vertebrates.
  • Thumbnail Image
    Item
    Open Access
    Sexual conflict predicts morphology and behavior in two species of penduline tits
    (BioMed Central Ltd, 2010) van Dijk, Rene; Pogany, Akos; Komdeur, Jan; Lloyd, Penn; Szekely, Tamas
    BACKGROUND:The evolutionary interests of males and females rarely coincide (sexual conflict), and these conflicting interests influence morphology, behavior and speciation in various organisms. We examined consequences of variation in sexual conflict in two closely-related passerine birds with contrasting breeding systems: the Eurasian penduline tit Remiz pendulinus (EPT) exhibiting a highly polygamous breeding system with sexually antagonistic interests over parental care, and the socially monogamous Cape penduline tit Anthoscopus minutus (CPT). We derived four a priori predictions from sexual conflict theory and tested these using data collected in Central Europe (EPT) and South Africa (CPT). Firstly, we predicted that EPTs exhibit more sexually dimorphic plumage than CPTs due to more intense sexual selection. Secondly, we expected brighter EPT males to provide less care than duller males. Thirdly, since song is a sexually selected trait in many birds, male EPTs were expected to exhibit more complex songs than CPT males. Finally, intense sexual conflict in EPT was expected to lead to low nest attendance as an indication of sexually antagonistic interests, whereas we expected more cooperation between parents in CPT consistent with their socially monogamous breeding system. RESULTS: Consistent with our predictions EPTs exhibited greater sexual dimorphism in plumage and more complex song than CPTs, and brighter EPT males provided less care than duller ones. EPT parents attended the nest less frequently and less simultaneously than CPT parents. CONCLUSIONS: These results are consistent with sexual conflict theory: species in which sexual conflict is more manifested (EPT) exhibited a stronger sexual dimorphism and more elaborated sexually selected traits than species with less intense sexual conflict (CPT). Our results are also consistent with the notion that EPTs attempt to force their partner to work harder as expected under sexual conflict: each member of the breeding pair attempts to shift the costs of care to the other parent. More brightly colored males benefit more from desertion than dull ones, because they are more likely to remate with a new female. Taken together, the comparison between two closely related species with contrasting breeding systems suggest that sexual conflict over care has influenced the evolution of behavior and morphology in penduline tits.
  • Thumbnail Image
    Item
    Open Access
    A study of the ecology of the Namaqua Sandgrouse and other arid-zone birds
    (1998) Lloyd, Penn; Crowe, Timothy M
    This field study set out to identify the key ecological factors influencing the population dynamics of the Namaqua Sandgrouse Pterocles namaqua, through an investigation of diet and the nutritional demands during different stages of the annual cycle, the timing of breeding seasons and movements in relation to patterns of rainfall-dependent food availability, breeding success and the factors limiting productivity. In addition, the nesting habits and success of 11 coexisting arid-zone bird species were examined to test a variety of hypotheses regarding the relationship between nest-predation rate and nest site, nest density, predator-avoidance behaviour, stage of the nesting cycle and season, and degree of residency. Furthermore, the importance of rainfall as a breeding stimulus and its effects on clutch size were investigated for several species. The Namaqua Sandgrouse is an obligate granivore at all times, feeding on the seeds of annual plants, primarily of the family Fabaceae. Even while breeding, energy is the first-limiting nutrient in the foods of adults. Growing chicks have a proportionally greater protein demand, and are more dependent than adults on protein-rich legume seeds to satisfy first-limiting amino acid requirements. The chick growth phase was identified as the most nutritionally demanding stage in the annual cycle. The breeding season was found to be unexpectedly variable, and not consistently correlated with periods of peak food availability.