Prevalence of avian haemosporidian parasites is positively related to the abundance of host species at multiple sites within a region.

Parasite prevalence is thought to be positively related to host population density owing to enhanced contagion. However, the relationship between prevalence and local abundance of multiple host species is underexplored. We surveyed birds and their haemosporidian parasites (genera Plasmodium and Haemoproteus) at multiple sites across eastern North America to test whether the prevalence of these parasites in a host species at a particular site is related to that host's local abundance. Prevalence was positively related to host abundance within most sites, although the effect was stronger and more consistent for Plasmodium than for Haemoproteus. In contrast, prevalence was not related to variation in the abundance of most individual host species among sites across the region. These results suggest that parasite prevalence partly reflects the relative abundances of host species in local assemblages. However, three nonnative host species had low prevalence despite being relatively abundant at one site, as predicted by the enemy release hypothesis.

Local host specialization, host-switching, and dispersal shape the regional distributions of avian haemosporidian parasites.

The drivers of regional parasite distributions are poorly understood, especially in comparison with those of free-living species. For vector-transmitted parasites, in particular, distributions might be influenced by host-switching and by parasite dispersal with primary hosts and vectors. We surveyed haemosporidian blood parasites (Plasmodium and Haemoproteus) of small land birds in eastern North America to characterize a regional parasite community. Distributions of parasite populations generally reflected distributions of their hosts across the region. However, when the interdependence between hosts and parasites was controlled statistically, local host assemblages were related to regional climatic gradients, but parasite assemblages were not. Moreover, because parasite assemblage similarity does not decrease with distance when controlling for host assemblages and climate, parasites evidently disperse readily within the distributions of their hosts. The degree of specialization on hosts varied in some parasite lineages over short periods and small geographic distances independently of the diversity of available hosts and potentially competing parasite lineages. Nonrandom spatial turnover was apparent in parasite lineages infecting one host species that was well-sampled within a single year across its range, plausibly reflecting localized adaptations of hosts and parasites. Overall, populations of avian hosts generally determine the geographic distributions of haemosporidian parasites. However, parasites are not dispersal-limited within their host distributions, and they may switch hosts readily.

Scatterhoarding rodents favor higher predation risks for cache sites: The potential for predators to influence the seed dispersal process.

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.

Hoarding without reward: rodent responses to repeated episodes of complete cache loss.

For food-hoarding strategies to be maintained in a population, the benefits of hoarding must outweigh the costs. If rewards are too low to offset the costs of hoarding, hoarders might be expected to abandon hoarding and/or shift to an alternative storing strategy (e.g., increase food consumption). However the ability to adjust to such circumstances requires that animals anticipate long-term rewards and adjust storing strategies to modify future outcomes. To test this, we subjected three sympatric food-hoarding species (the Korean field mouse, Apodemus peninsulae, both a scatter and larder hoarder; the Chinese white-bellied rat, Niviventer confucianus, only a larder hoarder; and Père David's rock squirrel, Sciurotamias davidianus, predominantly a scatter hoarder) to repeated episodes of complete cache loss over nine sequential trials in semi-natural enclosures. Although these species increased harvest and consumption rates throughout the experiment, none of these three species ceased hoarding under these conditions. The variation in responses observed across species and gender suggest some degree of behavioural plasticity to compensate for such extreme losses, but a general inability to abandon hoarding or shift to an alternative strategy. Future studies should consider how such responses correspond to natural patterns of intensive pilferage in the field.

Does multiple seed loading in Blue Jays result in selective dispersal of smaller acorns?

Studies from both tropical and temperate systems show that scatter-hoarding rodents selectively disperse larger seeds farther from their source than smaller seeds, potentially increasing seedling establishment in larger-seeded plants. Size-biased dispersal is evident in many oaks (Quercus) and is true both across and within species. Here, we predict that intraspecifc variation in seed size also influences acorn dispersal by the Blue Jay (Cyanocitta cristata Linnaeus), but in an opposite manner. Blue Jays are gape-limited and selectively disperse smaller acorn species (e.g. pin oaks [Quercus palustris Münchh]), but often carry several acorns in their crop during a single dispersal event. We predict that jays foraging on smaller acorns will load more seeds per trip and disperse seeds to greater distances than when single acorns are carried in the bill. To test this, we presented free-ranging Blue Jays with pin oak acorns of different sizes over a 2-year period. In each of 16 experimental trials, we monitored the birds at a feeding station with remote cameras and determined the number of acorns removed and the distance acorns were dispersed when cached. Jays were significantly more likely to engage in multiple seed loading with smaller seeds in both years of the study. During the second year, these smaller acorns were dispersed farther than larger acorns, and during the first year, larger acorns were dispersed farther, revealing an inconsistent response to seed size during our study. We suggest that in some circumstances, multiple seed loading by Blue Jays may favor dispersal in some plant species.