Life history trade-offs between survival, moult and breeding in a tropical season environment

Birds--Reproduction--Climatic factors;Birds--Reproduction--Africa, West;Molting

Stevens, Matthew C. ; Cresswell, Will ; Cresswell, Will

University:University of St Andrews

Department:Biology (School of)

关键词: Birds--Reproduction--Climatic factors;    Birds--Reproduction--Africa, West;    Molting;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/1857/MatthewStevensPhDThesis.PDF?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

The trade-off between current and future investment in reproduction lies at the heart of lifehistory theory. The need to differentially allocate resources between these two options arisesgenerally as a result of environmental pressures. Higher risk of mortality in adults is linkedwith increased investment in current reproduction, whereas the opposite is true where adultsare long-lived (the r- K selection paradigm). Perhaps the most obvious factors influencing theenvironment stem from seasonality of the climate, since rainfall and temperature affect foodavailability, resulting in a higher risk of mortality. The available trade-offs that an organismcan make will therefore be constrained by environmental variability potentially resulting ingeneral adaptation and so ultimately influencing evolution of biome-specific life-history traits.In this thesis, I examine how the seasonality of a West African tropical savannah environmentinfluences moult and breeding timing and duration, and survival in West African tropicalsavannah bird species. I show that moult in tropical birds follows the same basic descendantpattern through the wing feathers, but is a much lengthier process than for temperate species(mean = 131 ± 11 days, N = 29 species), and that it frequently overlaps with breedingactivities. This suggests either that either the feathers of tropical species take longer to grow;that it is a relatively low-cost activity and has little influence on life history trade-offs; or thatindividuals further aim to reduce mortality risk by attempting to maintain high flight capabilityat all times. Breeding also occurred over a longer season than for temperate species,although an obvious peak in occurrence was identified to coincide with the food-abundantperiod of the late rains and early dry season. Lengthy breeding seasons may indicate anincreased tendency to re-nest (possibly as a result of higher nest predation levels), and wealso identified a prolonged immature plumage phase – potentially indicating an extendedduration of parental care. Survival rates were calculated from mark-recapture models basedon mist-netting data. Previous work has focussed on the use of incorporating mark-resightingdata alongside that obtained by standard mark-recapture techniques. Here, I assess themodels applied in those methods, identify problems associated with over-paramaterisation,goodness of fit and the generation of biologically unrealistic estimates, and so providesuggestions on how to improve the protocol. Average survival from my study (40 species:0.63 ± 0.02) was higher than previous estimates obtained from this site and were comparablewith estimates from other Afrotropical and Neotropical areas, although rates varied greatlybetween species. Juvenile survival (13 species) was similar or possibly lower than adultsurvival. I then used my empirically derived estimates of moult, breeding and survival lifehistory traits to identify potential trade-offs between traits. Overall I was unable to identifysignificant relationships between any of the life history trait estimates, other than betweenadult survival and clutch size. In this, the results followed those of previous researchers inidentifying a pattern of lower investment in current reproduction (clutch size) andmaximisation of adult survival in tropical species. My study, however, demonstrates for thefirst time how moult and breeding duration are likely to be less constrained in tropicalenvironments.