Rodent-mediated plant community competition:what happens to the seeds after entering the adjacent stands?

Background:Seed dispersal by scatter-hoarding animals can affect the developmental dynamics of plant communities.However,how animals might participate in plant inter-community competition has rarely been investigated.Forest community junction is an area where the competition between plant communities is most prominent and animal activity is more frequent.At present,little is known about how scatter-hoarding animals might assist competitions by adjacent plant communities.Thus,for 3 years(2015–2017),we tracked the fate of 2880 tagged seeds(Quercus aliena var.acuteserrata,Pinus tabuliformis,and P.armandii seed)placed near an edge where the forest composition changes from a pine forest to an oak forest in northwestern China.Results:We found that the seed fates differed when Quercus and Pinus seeds entered adjacent stands.In contrast to Pinus seeds,acorns that entered pine forests were characterized by higher caching rates and longer dispersal distances.Pinus seeds had the highest probability of being predated(85%)by rodents,and eleven Q.aliena var.acuteserrata seedlings were established in pine forests,although none survived in the later stages.In addition,rodents exhibited obvious selectivity in terms of the microhabitats for the seed caching sites.Conclusions:Seed fates differed when Quercus and Pinus seeds entered adjacent stands.The predation pressure by rodents on the seeds of Pinus species limited the germination of seeds and seedling establishment in oak forests.The different seed fates after their bidirectional dispersal could affect the differences in natural regeneration between pine and oak forests,and they might increase the recruitment rates for oak at the edge of an adjacent community.Rodent-mediated seed dispersal could potential unintentionally affect the competition between plant communities.

Spatially biased dispersal of acorns by a scatter-hoarding corvid may accelerate passive restoration of oak habitat on California＇s largest island

Scatter hoarding by corvids （crows, jays, magpies, and nutcrackers） provides seed dispersal for many large-seeded plants, including oaks and pines. When hoarding seeds, corvids often choose nonrandom locations throughout the landscape, resulting in differential survival of seeds. In the context of habitat restoration, such disproportional storing of seeds in areas suitable for germin- ation and establishment can accelerate expansion and recovery of large-seeded tree populations and their associated ecosystems. Here, we investigate the spatial preferences of island scrub jays Aphelocoma insularis during scatter hoarding of acorns （Quercus spp.） on Santa Cruz Island. We use a large behavioral data set on the birds＇ behavior in combination with seedling surveys and spatial analysis to determine whether 1） island scrub jays disproportionally cache seeds in specific habitat types, and 2） whether the preferred habitat type is suitable for oak regeneration. Our results show that the jays nonrandomly cache acorns across the landscape; they use chaparral and coastal sage scrub disproportionally while avoiding open and grassy areas. The areas used most often for caching were also the areas with the highest oak seedling densities. We discuss the potential role of these findings for the recovery of Santa Cruz Island＇s oak habitat since the 1980s.

Differentiation in seed hoarding among three sympatric rodent species in a warm temperate forest

Although seed hoarding by rodents has been extensively studied,differentiation in seed-hoarding behaviors among sympatric rodent species has not been well investigated.Using semi-natural enclosures,we demonstrated that three sympatric rodent species showed clear differentiation in food selection,scatter versus larder hoarding behaviors and eating behaviors when offered seeds of four plant species from a warm temperate forest in northern China.The large field mouse Apodemus peninsulae preferred seeds of wild apricot(Prunus armeniaca)and Liaodong oak(Quercus liaotungensis),whereas the Chinese white-bellied rat Niviventor confucianus preferred seeds of cultivated walnut and Liaodong oak,and the David’s rock squirrel Sciurotamias davidianus preferred seeds of cultivated walnut,wild apricot and Liaodong oak.All three rodents showed larder hoarding of seeds from all four plant species,but the large field mouse showed scatter hoarding of wild apricot,and the David’s rock squirrel showed scatter hoarding of Liaodong oak and wild walnut.Acorns of Liaodong oak,which have a soft seed hull,were more often eaten in situ,whereas wild walnuts,which have a hard seed hull and more tannin,were less hoarded by all rodent species.Differentiation in the scatter versus larder hoarding behaviors of sympatric rodent species suggests that sympatric rodents play different roles in the regeneration of different sympatric plant species.

Effects of insect infestation on rodent-mediated dispersal of Quercus aliena:results from field and enclosure experiments

Rodents influence plant establishment and regeneration by functioning as both seed predators and dispersers.However,these rodent-plant interactions can vary significantly due to various environmental conditions and the activity of other insect seed predators.Here,we use a combination of both field and enclosure(i.e.individual cage and semi-natural enclosure)experiments,to determine whether rodents can distinguish sound seeds from those infested with insects.We also demonstrate how such responses to insects are influenced by food abun-dance and other environmental factors.We presented rodents with 2 kinds of Quercus aliena seeds(sound and insect-infested seeds)in a subtropical forest in the Qinling Mountains,central China,from September to No-vember of 2011 to 2013.The results showed that rodents preferred to hoard and eat sound seeds than infested seeds in the field and semi-natural enclosure,while they preferred to eat infested seeds over sound seeds in the individual cages.In addition,both hoarding and eating decisions were influenced by food abundance.Rodents hoarded more sound seeds in years of high food abundance while they consumed more acorns in years of food shortage.Compared with field results,rodents reduced scatter-hoarding behavior in semi-natural enclosures and ate more insect-infested seeds in smaller individual cages.These results further confirm that rodents distinguish infested seeds from non-infested seeds but demonstrate that this behavior varies with conditions(i.e.environ-ment and food abundance).We suggest that such interactions will influence the dispersal and natural regenera-tion of seeds as well as predation rates on insect larvae.

Effects of rodent abundance and richness on cache pilfering

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.

Neighborhood effects on the tannin-related foraging decisions of two rodent species under semi-natural conditions

Neighborhood effects on seed predation and dispersal processes are usually seed-characteristic-dependent;however,how seeds with certain characteristics affect the foraging behavior of rodents in relation to other seeds nearby is unclear.Because large differences in seed characteristics between neighboring seeds may lead to significant differences in rodent foraging preferences,we hypothesized that neighborhood effects were more likely to be detected when paired seeds differed in seed characteristics.We investigated the foraging decisions of two rodent species,the red spiny rat Maxomys surifer and the Chinese white-bellied rat Niviventer confucianus,in semi-natural enclosures by presenting them with artificial seeds containing different levels of tannin(0,3%,and 6%tannin).Both rodents showed similar preferences and preferentially consumed high-tannin seeds(6%tannin)and scatter hoarded low-tannin seeds(0 tannin).The scatter hoarding of low-tannin(0 tannin)and high-tannin(6%tannin)seeds was significantly higher when these seeds were neighboring higher-tannin seeds than when they neighbored lowertannin seeds,whereas the scatter hoarding of intermediate-tannin seeds(3%tannin)varied little when they had different neighbors.High-tannin-seed(6%tannin)scatter hoarding was lowest when they neighbored low-tannin seeds(0 tannin),while low-tannin-seed(0 tannin)scatter hoarding was highest when they neighbored high-tannin seeds(6%tannin).Therefore,the seeds that the rodents scatter hoarded were next to(neighbored)seeds that they preferred to eat immediately,and vice versa.Our findings suggest that seed neighborhood effects affect rodent foraging behavior and the relationship between plants and rodents,and may have a profound effect on the regeneration and spatial structure of plant communities.