Effects of rodent abundance and richness on cache pilfering

Abstract

Scatterhoarding is a common behavioral strategy to conserve food during periods of scarcity, but this type of food storage is vulnerable to theft or pilferage. A variety of environmental factors and cache characteristics influence the rate of pilferage. Here we investigate 2 environmental factors, which heretofore have not received much attention: the abundance and species richness of scatterhoarding animals in the vicinity of scatterhoarded seeds. We measured the rate of cache pilferage at 7 sites that differed in the number and species composition of granivorous rodents in western Nevada using local native seeds and sunflower seeds. We found that there was no difference between the pilferage rate of native seeds and sunflower seeds, but that sites with different rodent abundances had different pilferage rates. Pilferage rates were proportional to the abundance of scatterhoarding rodents. Scatterhoarding rodents removed seeds at the rate of 1.3%/day/rodent individual. Species richness of scatterhoarding rodents was not correlated with rates of pilferage. These results suggest that density-dependent competition for scatterhoarded seeds is a strong determinant of pilferage rates.

Scatter‐hoarding and cache pilfering of rodents in response to seed abundance

“…Our results are also contrary to the conventional model that caches are pilfered at higher rates at lower seed abundance (Gálvez et al, ; Stapanian & Smith, , ). Recent study showed cache pilfering was highly dependent on rodent abundance (Dittel & Vander Wall, ), indicating that rodent abundance may be a larger factor than seed availability in affecting cache pilfering as scatter‐hoarder behavior is often driven by the seed:scatter‐hoarder ratio (Theimer, ; Zwolak & Crone, ). This may explain why cache pilfering rates are similar between the two seed rain periods of Q. mongolica , in which there was no difference in rodent abundances.…”

“…Several other studies have shown the tendency for rodents to cache fewer seeds when seed availability is high (Celis-Diez & Bustamante, 2005;Celis-Diez, Bustamante, & Vasquez, 2004;Sundaram, Lichti, Steele, Dalgleish, & Swihart, 2017). Although animals may store more seeds than they can consume when seed availability is high (Dittel & Vander Wall, 2018), rodents may have more opportunities to acquire food rather than recover their own caches at high level of seed abundance (Moore, McEuen, Swihart, Contreras, & Steele, 2007). Therefore, it is plausible that rodents spend more time foraging rather than caching, or even stop caching entirely in the face of a surfeit of food (Theimer, 2005).…”

“…However, studies of the mechanisms of cache pilferage by rodents may encounter methodological difficulties (Jansen et al, ), although Daly, Jacobs, Wilson, and Behrends () demonstrated a high rate of cache pilferage by provisioning kangaroo rats with dyed food. Recently, Dittel and Vander Wall () investigated cache pilfering at community level and found that rates of pilferage are likely to rise with increases in the number of animals.…”

“…Although little is known about pilfering behavior in most species, it is widely assumed that pilferage is common in both scatter-hoarders and larder-hoarders (Steele & Koprowski, 2001;Wang et al, 2018). Because of the significance of cache pilfering, understanding how cache pilfering occurs is a fundamental question in seed dispersal ecology (Dittel, Perea, & Vander Wall, 2017;Dittel & Vander Wall, 2018). However, studies of the mechanisms of cache pilferage by rodents may encounter methodological difficulties (Jansen et al, 2012), although Daly, Jacobs, Wilson, and Behrends (1992) demonstrated a high rate of cache pilferage by provisioning kangaroo rats with dyed food.…”

Exclusion of interspecific competition reduces scatter‐hoarding of Siberian chipmunk Tamias sibiricus: A field study

“…Among seed predators, however, rigorous intraspecific and interspecific competition for limited food resources is also widely witnessed (Christensen & Whitham 1993;Thayer & Vander Wall 2005). Therefore, the availability of seeds and the abundance of seed predators/dispersers can affect the quality and quantity of seed dispersal by altering per capita seed abundance (García et al 2007;García & Martinez 2012;Xiao et al 2013;Dittel & Vander Wall 2018).…”