Life history trade-offs between survival, moult and breeding in a tropical season environment
Year: 2011
Type: dissertation
Abstract: The trade-off between current and future investment in reproduction lies at the heart of life\nhistory theory. The need to differentially allocate resources between these two options arises\ngenerally as a result of environmental pressures. Higher risk of mortality in adults is linked\nwith increased investment in current reproduction, whereas the opposite is true where adults\nare long-lived (the r- K selection paradigm). Perhaps the most obvious factors influencing the\nenvironment stem from seasonality of the climate, since rainfall and temperature affect food\navailability, resulting in a higher risk of mortality. The available trade-offs that an organism\ncan make will therefore be constrained by environmental variability potentially resulting in\ngeneral adaptation and so ultimately influencing evolution of biome-specific life-history traits.\nIn this thesis, I examine how the seasonality of a West African tropical savannah environment\ninfluences moult and breeding timing and duration, and survival in West African tropical\nsavannah bird species. I show that moult in tropical birds follows the same basic descendant\npattern through the wing feathers, but is a much lengthier process than for temperate species\n(mean = 131 ± 11 days, N = 29 species), and that it frequently overlaps with breeding\nactivities. This suggests either that either the feathers of tropical species take longer to grow;\nthat it is a relatively low-cost activity and has little influence on life history trade-offs; or that\nindividuals further aim to reduce mortality risk by attempting to maintain high flight capability\nat all times. Breeding also occurred over a longer season than for temperate species,\nalthough an obvious peak in occurrence was identified to coincide with the food-abundant\nperiod of the late rains and early dry season. Lengthy breeding seasons may indicate an\nincreased tendency to re-nest (possibly as a result of higher nest predation levels), and we\nalso identified a prolonged immature plumage phase – potentially indicating an extended\nduration of parental care. Survival rates were calculated from mark-recapture models based\non mist-netting data. Previous work has focussed on the use of incorporating mark-resighting\ndata alongside that obtained by standard mark-recapture techniques. Here, I assess the\nmodels applied in those methods, identify problems associated with over-paramaterisation,\ngoodness of fit and the generation of biologically unrealistic estimates, and so provide\nsuggestions on how to improve the protocol. Average survival from my study (40 species:\n0.63 ± 0.02) was higher than previous estimates obtained from this site and were comparable\nwith estimates from other Afrotropical and Neotropical areas, although rates varied greatly\nbetween species. Juvenile survival (13 species) was similar or possibly lower than adult\nsurvival. I then used my empirically derived estimates of moult, breeding and survival life\nhistory traits to identify potential trade-offs between traits. Overall I was unable to identify\nsignificant relationships between any of the life history trait estimates, other than between\nadult survival and clutch size. In this, the results followed those of previous researchers in\nidentifying a pattern of lower investment in current reproduction (clutch size) and\nmaximisation of adult survival in tropical species. My study, however, demonstrates for the\nfirst time how moult and breeding duration are likely to be less constrained in tropical\nenvironments.
Author: Matthew Stevens
Language: English
Topic: Avian ecology and behavior
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
Funder: Durham University
OpenAlex ID: W1608168678