Scatterhoarding rodents often place caches in the open where pilferage rates are reduced,suggesting that they tradeoff higher risks of predation for more secure cache sites.We tested this hypothesis in two study syste...Scatterhoarding rodents often place caches in the open where pilferage rates are reduced,suggesting that they tradeoff higher risks of predation for more secure cache sites.We tested this hypothesis in two study systems by measuring predation risks inferred from measures of giving-up densities(GUDs)at known cache sites and other sites for comparison.Rodent GUDs were measured with small trays containing 3 L of fine sand mixed with sunflower seeds.In the first experiment,we relied on a 2-year seed dispersal study in a natural forest to identify caches of eastern gray squirrels(Sciurus carolinensis)and then measured GUDs at:(i)these caches;(ii)comparable points along logs and rocks where rodent activity was assumed highest;and(iii)a set of random points.We found that GUDs and,presumably,predation risks,were higher at both cache and random points than those with cover.At the second site,we measured GUDs of eastern gray squirrels in an open park system and found that GUDs were consistently lowest at the base of the tree compared to more open sites,where previous studies show caching by squirrels to be highest and pilferage rates by naïve competitors to be lowest.These results confirm that predation risks can influence scatterhoarding decisions but that they are also highly context dependent,and that the landscape of fear,now so well documented in the literature,could potentially shape the temporal and spatial patterns of seedling establishment and forest regeneration in systems where scatterhoarding is common.展开更多
The sizes of both seed dispersers and seeds are traits that are likely to interact to influence seed fate in many synzoochoric plant species.Here,we examined whether members of a granivorous rodent community consist&#...The sizes of both seed dispersers and seeds are traits that are likely to interact to influence seed fate in many synzoochoric plant species.Here,we examined whether members of a granivorous rodent community consisting of species of different body size vary in their effectiveness as seed dispersers,and how this relationship may be altered by seed size.We marked northern red oak(Quercus rubra)acorns with plastic tags and placed them in size-selective rodent exclosures.The exclosures allowed differential access of rodent groups based on different body size:(i)small(e.g.Peromyscus spp.);(ii)small and medium(e.g.Tamias striatus);and(iii)small,medium and large(e.g.Sciurus carolinensis)species of rodents.Acorn removal did not differ among exclosure types,but more seeds were missing when removed by small rodents,probably because of larderhoarding.The treatments did not influence the relative frequency of acorn consumption.However,small rodents cached considerably fewer and partially ate more acorns than the other 2 groups.The mean dispersal distance was the longest for cages with medium openings,intermediate for cages with large openings and the shortest for cages with small openings.Acorn mass positively affected the probability of caching and this relationship was unaffected by exclosure type.In conclusion,granivorous rodents of different body sizes strongly differed in their interactions with acorns,with small rodents acting primarily as acorn predators and medium and large species contributing significantly more to dispersal of red oaks.展开更多
基金We thank J.Healey and P.Lello for assistance with fieldwork and N.Lichti,R.K.Swihart and S.Agosta for earlier discussions on the potential for predators to impact patterns of cache placement by scatterhoarders and,in turn,the seed dispersal process.This study was in part supported by a Bullard Fellowship from Harvard Forest,Harvard University(to MAS),Wilkes University mentoring Fund,the U.S.National Science Foundation(DEB-12540642594)to MAS and the Howard Hughes Medical Institute to Wilkes University.
文摘Scatterhoarding rodents often place caches in the open where pilferage rates are reduced,suggesting that they tradeoff higher risks of predation for more secure cache sites.We tested this hypothesis in two study systems by measuring predation risks inferred from measures of giving-up densities(GUDs)at known cache sites and other sites for comparison.Rodent GUDs were measured with small trays containing 3 L of fine sand mixed with sunflower seeds.In the first experiment,we relied on a 2-year seed dispersal study in a natural forest to identify caches of eastern gray squirrels(Sciurus carolinensis)and then measured GUDs at:(i)these caches;(ii)comparable points along logs and rocks where rodent activity was assumed highest;and(iii)a set of random points.We found that GUDs and,presumably,predation risks,were higher at both cache and random points than those with cover.At the second site,we measured GUDs of eastern gray squirrels in an open park system and found that GUDs were consistently lowest at the base of the tree compared to more open sites,where previous studies show caching by squirrels to be highest and pilferage rates by naïve competitors to be lowest.These results confirm that predation risks can influence scatterhoarding decisions but that they are also highly context dependent,and that the landscape of fear,now so well documented in the literature,could potentially shape the temporal and spatial patterns of seedling establishment and forest regeneration in systems where scatterhoarding is common.
基金supported by(Polish)National Science Centre grant 2012/04/M/NZ8/00674.
文摘The sizes of both seed dispersers and seeds are traits that are likely to interact to influence seed fate in many synzoochoric plant species.Here,we examined whether members of a granivorous rodent community consisting of species of different body size vary in their effectiveness as seed dispersers,and how this relationship may be altered by seed size.We marked northern red oak(Quercus rubra)acorns with plastic tags and placed them in size-selective rodent exclosures.The exclosures allowed differential access of rodent groups based on different body size:(i)small(e.g.Peromyscus spp.);(ii)small and medium(e.g.Tamias striatus);and(iii)small,medium and large(e.g.Sciurus carolinensis)species of rodents.Acorn removal did not differ among exclosure types,but more seeds were missing when removed by small rodents,probably because of larderhoarding.The treatments did not influence the relative frequency of acorn consumption.However,small rodents cached considerably fewer and partially ate more acorns than the other 2 groups.The mean dispersal distance was the longest for cages with medium openings,intermediate for cages with large openings and the shortest for cages with small openings.Acorn mass positively affected the probability of caching and this relationship was unaffected by exclosure type.In conclusion,granivorous rodents of different body sizes strongly differed in their interactions with acorns,with small rodents acting primarily as acorn predators and medium and large species contributing significantly more to dispersal of red oaks.
