Density‐Dependent Foraging and Interference Competition by Common Gartersnakes are Temperature Dependent

Abstract

The ideal free distribution (IFD) predicts that optimal foragers will select foraging patches to maximize food rewards and that groups of foragers should thus be distributed between food patches in proportion to the availability of food in those patches. Because many of the underlying mechanisms of foraging are temperature dependent in ectotherms, the distribution of ectothermic foragers between food patches may similarly depend on temperature because the difference in fitness rewards between these patches may change with temperature. We tested the hypothesis that the distribution of Common Gartersnakes (Thamnophis sirtalis) between food patches can be explained by an IFD, but that conformance to an IFD weakens as temperature departs from the optimal temperature because fitness rewards, interference competition and the number of individuals foraging are highest at the optimal temperature. First, we determined the optimal temperature for foraging. Second, we examined group foraging at three temperatures and three density treatments. Search time was optimized at 27°C, handling time at 29°C and digestion time at 32°C. Gartersnakes did not match an IFD at any temperature, but their distribution did change with temperature: snakes at 20°C and at 30°C selected both food patches equally, while snakes at 25°C selected the low food patch more at low density and the high food patch more at high density. Food consumption and competition increased with temperature, and handling time decreased with temperature. Temperature therefore had a strong impact on foraging, but did not affect the IFD. Future work should examine temperature‐dependent foraging in ectotherms that are known to match an IFD.

Can temperature modify the strength of density‐dependent habitat selection in ectotherms? A test with red flour beetles

“…Ideal knowledge should not be violated at lower temperatures, but it will take individuals longer to sample habitats. Competitive abilities should be affected by temperature because the ability of ectotherms to extract resources decreases as temperature deviates from the optimal temperature; snakes, for instance, fight over food more intensely at the optimal temperature than at sub‐optimal temperatures (Halliday & Blouin‐Demers, ). Changing temperature, however, should not affect the equality of competitors because temperature should affect all individuals equally.…”

“…p will be highest at T o and will approach zero as temperature deviates from T o . E i should similarly approach zero as temperature deviates from T o due to the temperature dependence of resource extraction (Halliday & Blouin-Demers, 2016b).…”

“…p should follow the same pattern as the thermal reaction norm for fitness because per capita resource demand (i.e. the amount of resources required per individual) will decrease as temperature deviates from T o : food consumption decreases as temperature deviates from T o (Stevenson et al ., ; Angilletta, Hill & Robson, ; Halliday & Blouin‐Demers, ). p will be highest at T o and will approach zero as temperature deviates from T o .…”

Harlequin Frogs (Lysapsus) prefer mild places to park

“…Additionally, the thermal sensitivity of ectotherms varies from thermal generalists, which perform well under a broad range of environmental temperature, to thermal specialists, whose performance is suitable only in a narrow temperature range (Angilletta, 2009). Consequently, environmental temperature influences most aspects of physiology and behavior of ectotherms, such as foraging ability (e.g., Dell et al, 2014;Halliday & Blouin-Demers, 2016), immune function (e.g., Wright & Cooper, 1981;Mondal & Rai, 2001), rates of feeding and growth (e.g., Huey & Stevenson, 1979;Dastansara et al, 2017) or locomotion (Whitehead et al, 1989;Knowles & Weigl, 1990;Lai et al, 2018). Finally, environmental temperature modulates locomotor performance, which is tightly linked with survival and consequently to fitness of individuals and populations (Huey & Berrigan, 2001;Husak et al, 2006;Seebacher & Walter, 2012).…”