An evaluation of density-dependent and density-independent influences on population growth rates in Weddell seals
Much of the existing literature that evaluates the roles of density-dependent and density-independent factors on population dynamics has been called into question in recent years because measurement errors were not properly dealt with in analyses. Using state–space models to account for measurement...
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ftdatacite:10.6084/m9.figshare.c.3300905 2023-05-15T13:53:19+02:00 An evaluation of density-dependent and density-independent influences on population growth rates in Weddell seals Rotella, Jay J. Link, William A. Nichols, James D. Hadley, Gillian L. Garrott, Robert A. Proffitt, Kelly M. 2016 https://dx.doi.org/10.6084/m9.figshare.c.3300905 https://figshare.com/collections/An_evaluation_of_density-dependent_and_density-independent_influences_on_population_growth_rates_in_Weddell_seals/3300905 unknown Figshare https://dx.doi.org/10.1890/08-0971.1 CC-BY http://creativecommons.org/licenses/by/3.0/us CC-BY Environmental Science Ecology FOS Biological sciences Collection article 2016 ftdatacite https://doi.org/10.6084/m9.figshare.c.3300905 https://doi.org/10.1890/08-0971.1 2021-11-05T12:55:41Z Much of the existing literature that evaluates the roles of density-dependent and density-independent factors on population dynamics has been called into question in recent years because measurement errors were not properly dealt with in analyses. Using state–space models to account for measurement errors, we evaluated a set of competing models for a 22-year time series of mark–resight estimates of abundance for a breeding population of female Weddell seals (Leptonychotes weddellii) studied in Erebus Bay, Antarctica. We tested for evidence of direct density dependence in growth rates and evaluated whether equilibrium population size was related to seasonal sea-ice extent and the Southern Oscillation Index (SOI). We found strong evidence of negative density dependence in annual growth rates for a population whose estimated size ranged from 438 to 623 females during the study. Based on Bayes factors, a density-dependence-only model was favored over models that also included environmental covariates. According to the favored model, the population had a stationary distribution with a mean of 497 females (SD = 60.5), an expected growth rate of 1.10 (95% credible interval = 1.08–1.15) when population size was 441 females, and a rate of 0.90 (95% credible interval = 0.87–0.93) for a population of 553 females. A model including effects of SOI did receive some support and indicated a positive relationship between SOI and population size. However, effects of SOI were not large, and including the effect did not greatly reduce our estimate of process variation. We speculate that direct density dependence occurred because rates of adult survival, breeding, and temporary emigration were affected by limitations on per capita food resources and space for parturition and pup-rearing. To improve understanding of the relative roles of various demographic components and their associated vital rates to population growth rate, mark–recapture methods can be applied that incorporate both environmental covariates and the seal abundance estimates that were developed here. An improved understanding of why vital rates change with changing population abundance will only come as we develop a better understanding of the processes affecting marine food resources in the Southern Ocean. Article in Journal/Newspaper Antarc* Antarctica Sea ice Southern Ocean Weddell Seals DataCite Metadata Store (German National Library of Science and Technology) Erebus Bay ENVELOPE(166.517,166.517,-77.733,-77.733) Soi ENVELOPE(30.704,30.704,66.481,66.481) Southern Ocean Weddell |
institution |
Open Polar |
collection |
DataCite Metadata Store (German National Library of Science and Technology) |
op_collection_id |
ftdatacite |
language |
unknown |
topic |
Environmental Science Ecology FOS Biological sciences |
spellingShingle |
Environmental Science Ecology FOS Biological sciences Rotella, Jay J. Link, William A. Nichols, James D. Hadley, Gillian L. Garrott, Robert A. Proffitt, Kelly M. An evaluation of density-dependent and density-independent influences on population growth rates in Weddell seals |
topic_facet |
Environmental Science Ecology FOS Biological sciences |
description |
Much of the existing literature that evaluates the roles of density-dependent and density-independent factors on population dynamics has been called into question in recent years because measurement errors were not properly dealt with in analyses. Using state–space models to account for measurement errors, we evaluated a set of competing models for a 22-year time series of mark–resight estimates of abundance for a breeding population of female Weddell seals (Leptonychotes weddellii) studied in Erebus Bay, Antarctica. We tested for evidence of direct density dependence in growth rates and evaluated whether equilibrium population size was related to seasonal sea-ice extent and the Southern Oscillation Index (SOI). We found strong evidence of negative density dependence in annual growth rates for a population whose estimated size ranged from 438 to 623 females during the study. Based on Bayes factors, a density-dependence-only model was favored over models that also included environmental covariates. According to the favored model, the population had a stationary distribution with a mean of 497 females (SD = 60.5), an expected growth rate of 1.10 (95% credible interval = 1.08–1.15) when population size was 441 females, and a rate of 0.90 (95% credible interval = 0.87–0.93) for a population of 553 females. A model including effects of SOI did receive some support and indicated a positive relationship between SOI and population size. However, effects of SOI were not large, and including the effect did not greatly reduce our estimate of process variation. We speculate that direct density dependence occurred because rates of adult survival, breeding, and temporary emigration were affected by limitations on per capita food resources and space for parturition and pup-rearing. To improve understanding of the relative roles of various demographic components and their associated vital rates to population growth rate, mark–recapture methods can be applied that incorporate both environmental covariates and the seal abundance estimates that were developed here. An improved understanding of why vital rates change with changing population abundance will only come as we develop a better understanding of the processes affecting marine food resources in the Southern Ocean. |
format |
Article in Journal/Newspaper |
author |
Rotella, Jay J. Link, William A. Nichols, James D. Hadley, Gillian L. Garrott, Robert A. Proffitt, Kelly M. |
author_facet |
Rotella, Jay J. Link, William A. Nichols, James D. Hadley, Gillian L. Garrott, Robert A. Proffitt, Kelly M. |
author_sort |
Rotella, Jay J. |
title |
An evaluation of density-dependent and density-independent influences on population growth rates in Weddell seals |
title_short |
An evaluation of density-dependent and density-independent influences on population growth rates in Weddell seals |
title_full |
An evaluation of density-dependent and density-independent influences on population growth rates in Weddell seals |
title_fullStr |
An evaluation of density-dependent and density-independent influences on population growth rates in Weddell seals |
title_full_unstemmed |
An evaluation of density-dependent and density-independent influences on population growth rates in Weddell seals |
title_sort |
evaluation of density-dependent and density-independent influences on population growth rates in weddell seals |
publisher |
Figshare |
publishDate |
2016 |
url |
https://dx.doi.org/10.6084/m9.figshare.c.3300905 https://figshare.com/collections/An_evaluation_of_density-dependent_and_density-independent_influences_on_population_growth_rates_in_Weddell_seals/3300905 |
long_lat |
ENVELOPE(166.517,166.517,-77.733,-77.733) ENVELOPE(30.704,30.704,66.481,66.481) |
geographic |
Erebus Bay Soi Southern Ocean Weddell |
geographic_facet |
Erebus Bay Soi Southern Ocean Weddell |
genre |
Antarc* Antarctica Sea ice Southern Ocean Weddell Seals |
genre_facet |
Antarc* Antarctica Sea ice Southern Ocean Weddell Seals |
op_relation |
https://dx.doi.org/10.1890/08-0971.1 |
op_rights |
CC-BY http://creativecommons.org/licenses/by/3.0/us |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.6084/m9.figshare.c.3300905 https://doi.org/10.1890/08-0971.1 |
_version_ |
1766258353710825472 |