Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals
Abstract Background Determining the relative contribution of intrinsic and extrinsic factors to fluctuations in population size, trends and demographic composition is analytically complex. It is often only possible to examine the combined effects of these factors through measurements made over long...
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ftbiomed:oai:biomedcentral.com:1472-6785-7-3 2023-05-15T16:05:40+02:00 Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals de Little, Siobhan C Bradshaw, Corey JA McMahon, Clive R Hindell, Mark A 2007-03-27 http://www.biomedcentral.com/1472-6785/7/3 en eng BioMed Central Ltd. http://www.biomedcentral.com/1472-6785/7/3 Copyright 2007 de Little et al; licensee BioMed Central Ltd. Research article 2007 ftbiomed 2007-11-11T15:25:46Z Abstract Background Determining the relative contribution of intrinsic and extrinsic factors to fluctuations in population size, trends and demographic composition is analytically complex. It is often only possible to examine the combined effects of these factors through measurements made over long periods, spanning an array of population densities or levels of food availability. Using age-structured mark-recapture models and datasets spanning five decades (1950–1999), and two periods of differing relative population density, we estimated age-specific probabilities of survival and examined the combined effects of population density and environmental conditions on juvenile survival of southern elephant seals at Macquarie Island. Results First-year survival decreased with density during the period of highest population size, and survival increased during years when the Southern Oscillation Index (SOI) anomaly (deviation from a 50-year mean) during the mother's previous foraging trip to sea was positive (i.e., El Niño). However, when environmental stochasticity and density were considered together, the effect of density on first-year survival effectively disappeared. Ignoring density effects also leads to models placing too much emphasis on the environmental conditions prevailing during the naïve pup's first year at sea. Conclusion Our analyses revealed that both the state of the environment and population density combine to modify juvenile survival, but that the degree to which these processes contributed to the variation observed was interactive and complex. This underlines the importance of evaluating the relative contribution of both the intrinsic and extrinsic factors that regulate animal populations because false conclusions regarding the importance of population regulation may be reached if they are examined in isolation. Article in Journal/Newspaper Elephant Seals Macquarie Island Southern Elephant Seals BioMed Central Soi ENVELOPE(30.704,30.704,66.481,66.481) |
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English |
description |
Abstract Background Determining the relative contribution of intrinsic and extrinsic factors to fluctuations in population size, trends and demographic composition is analytically complex. It is often only possible to examine the combined effects of these factors through measurements made over long periods, spanning an array of population densities or levels of food availability. Using age-structured mark-recapture models and datasets spanning five decades (1950–1999), and two periods of differing relative population density, we estimated age-specific probabilities of survival and examined the combined effects of population density and environmental conditions on juvenile survival of southern elephant seals at Macquarie Island. Results First-year survival decreased with density during the period of highest population size, and survival increased during years when the Southern Oscillation Index (SOI) anomaly (deviation from a 50-year mean) during the mother's previous foraging trip to sea was positive (i.e., El Niño). However, when environmental stochasticity and density were considered together, the effect of density on first-year survival effectively disappeared. Ignoring density effects also leads to models placing too much emphasis on the environmental conditions prevailing during the naïve pup's first year at sea. Conclusion Our analyses revealed that both the state of the environment and population density combine to modify juvenile survival, but that the degree to which these processes contributed to the variation observed was interactive and complex. This underlines the importance of evaluating the relative contribution of both the intrinsic and extrinsic factors that regulate animal populations because false conclusions regarding the importance of population regulation may be reached if they are examined in isolation. |
format |
Article in Journal/Newspaper |
author |
de Little, Siobhan C Bradshaw, Corey JA McMahon, Clive R Hindell, Mark A |
spellingShingle |
de Little, Siobhan C Bradshaw, Corey JA McMahon, Clive R Hindell, Mark A Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals |
author_facet |
de Little, Siobhan C Bradshaw, Corey JA McMahon, Clive R Hindell, Mark A |
author_sort |
de Little, Siobhan C |
title |
Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals |
title_short |
Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals |
title_full |
Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals |
title_fullStr |
Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals |
title_full_unstemmed |
Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals |
title_sort |
complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals |
publisher |
BioMed Central Ltd. |
publishDate |
2007 |
url |
http://www.biomedcentral.com/1472-6785/7/3 |
long_lat |
ENVELOPE(30.704,30.704,66.481,66.481) |
geographic |
Soi |
geographic_facet |
Soi |
genre |
Elephant Seals Macquarie Island Southern Elephant Seals |
genre_facet |
Elephant Seals Macquarie Island Southern Elephant Seals |
op_relation |
http://www.biomedcentral.com/1472-6785/7/3 |
op_rights |
Copyright 2007 de Little et al; licensee BioMed Central Ltd. |
_version_ |
1766401570617950208 |