Limits...
Determination of foraging thresholds and effects of application on energetic carrying capacity for waterfowl.

Hagy HM, Kaminski RM - PLoS ONE (2015)

Bottom Line: Energetic carrying capacity of habitats for wildlife is a fundamental concept used to better understand population ecology and prioritize conservation efforts.We created foraging patches with different fixed prey densities and monitored the numerical and behavioral responses of waterfowl (Anatidae) and depletion of foods during winter.We describe implications on habitat conservation objectives of using different foraging thresholds in energetic carrying capacity models and suggest scientists reevaluate assumptions of these models used to guide habitat conservation.

View Article: PubMed Central - PubMed

Affiliation: Forbes Biological Station-Bellrose Waterfowl Research Center, Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Havana, Illinois, United States of America.

ABSTRACT
Energetic carrying capacity of habitats for wildlife is a fundamental concept used to better understand population ecology and prioritize conservation efforts. However, carrying capacity can be difficult to estimate accurately and simplified models often depend on many assumptions and few estimated parameters. We demonstrate the complex nature of parameterizing energetic carrying capacity models and use an experimental approach to describe a necessary parameter, a foraging threshold (i.e., density of food at which animals no longer can efficiently forage and acquire energy), for a guild of migratory birds. We created foraging patches with different fixed prey densities and monitored the numerical and behavioral responses of waterfowl (Anatidae) and depletion of foods during winter. Dabbling ducks (Anatini) fed extensively in plots and all initial densities of supplemented seed were rapidly reduced to 10 kg/ha and other natural seeds and tubers combined to 170 kg/ha, despite different starting densities. However, ducks did not abandon or stop foraging in wetlands when seed reduction ceased approximately two weeks into the winter-long experiment nor did they consistently distribute according to ideal-free predictions during this period. Dabbling duck use of experimental plots was not related to initial seed density, and residual seed and tuber densities varied among plant taxa and wetlands but not plots. Herein, we reached several conclusions: 1) foraging effort and numerical responses of dabbling ducks in winter were likely influenced by factors other than total food densities (e.g., predation risk, opportunity costs, forager condition), 2) foraging thresholds may vary among foraging locations, and 3) the numerical response of dabbling ducks may be an inconsistent predictor of habitat quality relative to seed and tuber density. We describe implications on habitat conservation objectives of using different foraging thresholds in energetic carrying capacity models and suggest scientists reevaluate assumptions of these models used to guide habitat conservation.

No MeSH data available.


Apparent existence energy and energy removed from plots during winter.Apparent existence energy and energy removed expressed as duck energy days (DED/ha ± standard error) in 0.5-ha plots supplemented in mid-December with low (50 kg/ha), medium (250 kg/ha), or high (550 kg/ha) densities of Japanese millet (Echinochloa frumentacea) in 4 experimental wetlands sampled from mid-December 2008—late February 2009 in eastern Mississippi, western Tennessee, and the Mississippi Alluvial Valley, USA.
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pone.0118349.g003: Apparent existence energy and energy removed from plots during winter.Apparent existence energy and energy removed expressed as duck energy days (DED/ha ± standard error) in 0.5-ha plots supplemented in mid-December with low (50 kg/ha), medium (250 kg/ha), or high (550 kg/ha) densities of Japanese millet (Echinochloa frumentacea) in 4 experimental wetlands sampled from mid-December 2008—late February 2009 in eastern Mississippi, western Tennessee, and the Mississippi Alluvial Valley, USA.

Mentions: Energy reduction in plots during early and mid-winter was not related to apparent existence energy (i.e., estimated existence energy required by ducks using plots during each time period; Fig. 3), but varied by treatment and survey period (,). Energy reduction was positively related to initial energy density and most removal occurred in late December with little to no removal from January through February. During early winter, energy reduction was positively related to initial energy density but was not related to apparent existence energy (,). Moreover, energy reduction during early winter from wetlands was greater than apparent existence energy in 9 of 12 plots. However, apparent existence energy exceeded energy reduction from early January–February 2009 in 11 of 12 treatment plots (Fig. 3), implying that foragers may have expended more energy within plots than they removed and use of alternative foraging habitats was required to maintain a neutral or positive energy balance.


Determination of foraging thresholds and effects of application on energetic carrying capacity for waterfowl.

Hagy HM, Kaminski RM - PLoS ONE (2015)

Apparent existence energy and energy removed from plots during winter.Apparent existence energy and energy removed expressed as duck energy days (DED/ha ± standard error) in 0.5-ha plots supplemented in mid-December with low (50 kg/ha), medium (250 kg/ha), or high (550 kg/ha) densities of Japanese millet (Echinochloa frumentacea) in 4 experimental wetlands sampled from mid-December 2008—late February 2009 in eastern Mississippi, western Tennessee, and the Mississippi Alluvial Valley, USA.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4366255&req=5

pone.0118349.g003: Apparent existence energy and energy removed from plots during winter.Apparent existence energy and energy removed expressed as duck energy days (DED/ha ± standard error) in 0.5-ha plots supplemented in mid-December with low (50 kg/ha), medium (250 kg/ha), or high (550 kg/ha) densities of Japanese millet (Echinochloa frumentacea) in 4 experimental wetlands sampled from mid-December 2008—late February 2009 in eastern Mississippi, western Tennessee, and the Mississippi Alluvial Valley, USA.
Mentions: Energy reduction in plots during early and mid-winter was not related to apparent existence energy (i.e., estimated existence energy required by ducks using plots during each time period; Fig. 3), but varied by treatment and survey period (,). Energy reduction was positively related to initial energy density and most removal occurred in late December with little to no removal from January through February. During early winter, energy reduction was positively related to initial energy density but was not related to apparent existence energy (,). Moreover, energy reduction during early winter from wetlands was greater than apparent existence energy in 9 of 12 plots. However, apparent existence energy exceeded energy reduction from early January–February 2009 in 11 of 12 treatment plots (Fig. 3), implying that foragers may have expended more energy within plots than they removed and use of alternative foraging habitats was required to maintain a neutral or positive energy balance.

Bottom Line: Energetic carrying capacity of habitats for wildlife is a fundamental concept used to better understand population ecology and prioritize conservation efforts.We created foraging patches with different fixed prey densities and monitored the numerical and behavioral responses of waterfowl (Anatidae) and depletion of foods during winter.We describe implications on habitat conservation objectives of using different foraging thresholds in energetic carrying capacity models and suggest scientists reevaluate assumptions of these models used to guide habitat conservation.

View Article: PubMed Central - PubMed

Affiliation: Forbes Biological Station-Bellrose Waterfowl Research Center, Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Havana, Illinois, United States of America.

ABSTRACT
Energetic carrying capacity of habitats for wildlife is a fundamental concept used to better understand population ecology and prioritize conservation efforts. However, carrying capacity can be difficult to estimate accurately and simplified models often depend on many assumptions and few estimated parameters. We demonstrate the complex nature of parameterizing energetic carrying capacity models and use an experimental approach to describe a necessary parameter, a foraging threshold (i.e., density of food at which animals no longer can efficiently forage and acquire energy), for a guild of migratory birds. We created foraging patches with different fixed prey densities and monitored the numerical and behavioral responses of waterfowl (Anatidae) and depletion of foods during winter. Dabbling ducks (Anatini) fed extensively in plots and all initial densities of supplemented seed were rapidly reduced to 10 kg/ha and other natural seeds and tubers combined to 170 kg/ha, despite different starting densities. However, ducks did not abandon or stop foraging in wetlands when seed reduction ceased approximately two weeks into the winter-long experiment nor did they consistently distribute according to ideal-free predictions during this period. Dabbling duck use of experimental plots was not related to initial seed density, and residual seed and tuber densities varied among plant taxa and wetlands but not plots. Herein, we reached several conclusions: 1) foraging effort and numerical responses of dabbling ducks in winter were likely influenced by factors other than total food densities (e.g., predation risk, opportunity costs, forager condition), 2) foraging thresholds may vary among foraging locations, and 3) the numerical response of dabbling ducks may be an inconsistent predictor of habitat quality relative to seed and tuber density. We describe implications on habitat conservation objectives of using different foraging thresholds in energetic carrying capacity models and suggest scientists reevaluate assumptions of these models used to guide habitat conservation.

No MeSH data available.