Abstract
Deciphering the causes of variation in reproductive success is a fundamental issue in ecology, as the number of offspring produced is an important driver of individual fitness and population dynamics. Little is known however, about how different factors interact to drive variation in reproduction, such as whether an individual's response to extrinsic conditions (e.g. food availability or predation) varies according to its intrinsic attributes (e.g. age, previous allocation of resources towards reproduction).
We used 29 years of reproductive data from marked female tawny owls and natural variation in food availability (field vole) and predator abundance (northern goshawk) to quantify the extent to which extrinsic and intrinsic factors interact to influence owl reproductive traits (breeding propensity, clutch size and nest abandonment).
Extrinsic and intrinsic factors appeared to interact to affect breeding propensity (which accounted for 83% of the variation in owl reproductive success). Breeding propensity increased with vole density, although increasing goshawk abundance reduced the strength of this relationship. Owls became slightly more likely to breed as they aged, although this was only apparent for individuals who had fledged chicks the year before.
Owls laid larger clutches when food was more abundant. When owls were breeding in territories less exposed to goshawk predation, 99.5% of all breeding attempts reached the fledging stage. In contrast, the probability of breeding attempts reaching the fledging stage in territories more exposed to goshawk predation depended on the amount of resources an owl had already allocated towards reproduction (averaging 87.7% for owls with clutches of 1-2 eggs compared to 97.5% for owls with clutches of 4-6 eggs).
Overall, our results suggested that changes in extrinsic conditions (predominantly food availability, but also predator abundance) had the greatest influence on owl reproduction. In response to deteriorating extrinsic conditions (fewer voles and more goshawks) owls appeared to breed more frequently, but allocated fewer resources per breeding attempt. However, intrinsic attributes also appeared to have a relatively small influence on how an individual responded to variation in extrinsic conditions, which indicates that reproductive decisions were shaped by a complex series of extrinsic and intrinsic trade-offs.
We used 29 years of reproductive data from marked female tawny owls and natural variation in food availability (field vole) and predator abundance (northern goshawk) to quantify the extent to which extrinsic and intrinsic factors interact to influence owl reproductive traits (breeding propensity, clutch size and nest abandonment).
Extrinsic and intrinsic factors appeared to interact to affect breeding propensity (which accounted for 83% of the variation in owl reproductive success). Breeding propensity increased with vole density, although increasing goshawk abundance reduced the strength of this relationship. Owls became slightly more likely to breed as they aged, although this was only apparent for individuals who had fledged chicks the year before.
Owls laid larger clutches when food was more abundant. When owls were breeding in territories less exposed to goshawk predation, 99.5% of all breeding attempts reached the fledging stage. In contrast, the probability of breeding attempts reaching the fledging stage in territories more exposed to goshawk predation depended on the amount of resources an owl had already allocated towards reproduction (averaging 87.7% for owls with clutches of 1-2 eggs compared to 97.5% for owls with clutches of 4-6 eggs).
Overall, our results suggested that changes in extrinsic conditions (predominantly food availability, but also predator abundance) had the greatest influence on owl reproduction. In response to deteriorating extrinsic conditions (fewer voles and more goshawks) owls appeared to breed more frequently, but allocated fewer resources per breeding attempt. However, intrinsic attributes also appeared to have a relatively small influence on how an individual responded to variation in extrinsic conditions, which indicates that reproductive decisions were shaped by a complex series of extrinsic and intrinsic trade-offs.
Original language | English |
---|---|
Pages (from-to) | 892-902 |
Number of pages | 11 |
Journal | Journal of Animal Ecology |
Volume | 85 |
Issue number | 4 |
Early online date | 3 May 2016 |
DOIs | |
Publication status | Published - Jul 2016 |
Bibliographical note
AcknowledgementsWe thank B. Sheldon and two anonymous reviewers for all their helpful comments on a previous version of the manuscript. Our thanks also go to M. Davison, B. Little, P. Hotchin, D. Anderson and all other field assistants for their help with data collection and Forest Enterprise, particularly Tom Dearnley and Neville Geddes for facilitating work in Kielder Forest. We are also grateful to C. Sutherland for his help and advice on statistical analyses. This work was partly funded by Natural Research Limited and a Natural Environment Research Council studentship NE/J500148/1 to SH and grant NE/F021402/1 to XL. Forest Research funded all the fieldwork on goshawks, tawny owls and field voles during 1973-1996. In addition, we are grateful to English Nature and the BTO for issuing licences to visit goshawk nest sites.
Keywords
- Accipiter gentilis
- breeding decisions
- breeding propensity
- clutch size
- juvenile survival
- life-history trade-offs
- northern goshawk
- reproductive strategies
- Strix aluco
- tawny owl
Fingerprint
Dive into the research topics of 'Food availability and predation risk, rather than intrinsic attributes are the main factors shaping the reproductive decisions of a long-lived predator'. Together they form a unique fingerprint.Datasets
-
Food availability and predation risk, rather than intrinsic attributes are the main factors shaping the reproductive decisions of a long-lived predator
Hoy, S. R. (Contributor), Millon, A. (Contributor), Petty, S. (Contributor), Whitfield, D. P. (Contributor) & Lambin, X. (Contributor), DRYAD, 1 Jan 2017
DOI: 10.5061/dryad.6n579, http://datadryad.org/stash/dataset/doi:10.5061/dryad.6n579
Dataset
-
Data from: Food availability and predation risk, rather than intrinsic attributes are the main factors shaping the reproductive decisions of a long-lived predator
Hoy, S. R. (Creator), Millon, A. (Creator), Petty, S. (Creator), Whitfield, P. D. (Creator) & Lambin, X. (Creator), Dryad Digital Repository, 9 Mar 2017
DOI: 10.5061/dryad.6n579
Dataset