Weak olfaction increases seed scatter‐hoarding by Siberian chipmunks: implication in shaping plant–animal interactions

Scatter‐hoarding of seeds by animals plays an essential role in seed dispersal of plants and in shaping plant–animal interactions in forest ecosystems, but the function of scatter‐hoarding behavior is still unclear. We hypothesize that weak olfactory cues between seeds and scatter‐hoarding animals would increase scatter‐hoarding. Using a rodent–plant system of Siberian chipmunks Tamias sibiricus and Korean pines Pinus koraiensis, we tested the effects on seed scatter‐hoarding intensity by measuring and modifying the seed odor intensities and the abilities of the animals to detect seed odor. Siberian chipmunks seemed to scatter‐hoard more seeds with weaker odor signals, and Siberian chipmunks with reduced olfactory ability scatter‐hoarded more seeds, supporting our hypothesis. Our studies suggest that olfaction may have played an important role in the evolution of the strength of seed odor and scatter‐hoarding behavior of animals, and in shaping plant–animal interactions.     

How intraspecific variation in seed‐dispersing animals matters for plants

Seed dispersal by animals is a complex phenomenon, characterized by multiple mechanisms and variable outcomes. Most researchers approach this complexity by analysing context‐dependency in seed dispersal and investigating extrinsic factors that might influence interactions between plants and seed dispersers. Intrinsic traits of seed dispersers provide an alternative way of making sense of the enormous variation in seed fates. I review causes of intraspecific variability in frugivorous and granivorous animals, discuss their effects on seed dispersal, and outline likely consequences for plant populations and communities. Sources of individual variation in seed‐dispersing animals include sexual dimorphism, changes associated with growth and ageing, individual specialization, and animal personalities. Sexual dimorphism of seed‐dispersing animals influences seed fate through diverse mechanisms that range from effects caused by sex‐specific differences in body size, to influences of male versus female cognitive functions. These differences affect the type of seed treatment (e.g. dispersal versus predation), the number of dispersed seeds, distance of seed dispersal, and likelihood that seeds are left in favourable sites for seeds or seedlings. The best‐documented consequences of individual differences associated with growth and ageing involve quantity of dispersed seeds and the quality of seed treatment in the mouth and gut. Individual specialization on different resources affects the number of dispersed plant species, and therefore the connectivity and architecture of seed‐dispersal networks. Animal personalities might play an important role in shaping interactions between plants and dispersers of their seeds, yet their potential in this regard remains overlooked. In general, intraspecific variation in seed‐dispersing animals often influences plants through effects of these individual differences on the movement ecology of the dispersers. Two conditions are necessary for individual variation to exert a strong influence on seed dispersal. First, the individual differences in traits should translate into differences in crucial characteristics of seed dispersal. Second, individual variation is more likely to be important when the proportions of particular types of individuals fluctuate strongly in a population or vary across space; when proportions are static, it is less likely that intraspecific differences will be responsible for changes in the dynamics and outcomes of plant–animal interactions. In conclusion, focusing on variation among foraging animals rather than on species averages might bring new, mechanistic insights to the phenomenon of seed dispersal. While this shift in perspective is unlikely to replace the traditional approach (based on the assumption that all important variation occurs among species), it provides a complementary alternative to decipher the enormous variation observed in animal‐mediated seed dispersal.     

Directed seed dispersal towards areas with low conspecific tree density by a scatter‐hoarding rodent

Scatter‐hoarding animals spread out cached seeds to reduce density‐dependent theft of their food reserves. This behaviour could lead to directed dispersal into areas with lower densities of conspecific trees, where seed and seedling survival are higher, and could profoundly affect the spatial structure of plant communities. We tested this hypothesis with Central American agoutis and Astrocaryum standleyanum palm seeds on Barro Colorado Island, Panama. We radio‐tracked seeds as they were cached and re‐cached by agoutis, calculated the density of adult Astrocaryum trees surrounding each cache, and tested whether the observed number of trees around seed caches declined more than expected under random dispersal. Seedling establishment success was negatively dependent on seed density, and agoutis carried seeds towards locations with lower conspecific tree densities, thus facilitating the escape of seeds from natural enemies. This behaviour may be a widespread mechanism leading to highly effective seed dispersal by scatter‐hoarding animals.     

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

Seed caching and reciprocal cache pilferage play an important role in the coexistence of food‐hoarding animals. Understanding what affects seed caching and how cache pilferage occurs is an important question in seed dispersal ecology. However, tracking seed fate and cache pilferage presents substantial practical difficulties. Siberian chipmunks Tamias sibiricus always remove the entire pericarp when scatter‐hoarding acorns of Mongolian oak Quercus mongolica, whereas wood mice Apodemus peninsulae often store whole acorns in their caches. These differences in behavior provide an opportunity to investigate unilateral cache pilferage of T. sibiricus from A. peninsulae in response to seed abundance. In this study, tagged acorns were released at the peak and end periods of seed rain from Q. mongolica. This allowed us to investigate seed caching and unilateral cache pilferage at different seed abundances. We found that a higher proportion of acorns were cached at lower level of seed abundance (toward the end of seed rain), mainly because T. sibiricus rather than A. peninsulae scatter‐hoarded significantly more acorns at this time. Cache distances decreased with increasing seed abundance, indicating that acorns were cached further away and into smaller caches at lower seed abundance. Unexpectedly, unilateral cache pilferage by T. sibiricus was not significantly influenced by seed abundance—remaining at around 28% during both periods of high and low seed abundance.     

Post‐dispersal seed recovery by animals: is it a plant‐ or an animal‐driven process?

The ability of animals to find and consume hoarded seeds (i.e. seed recovery) is a key stage within the seed dispersal process. However, the ecology of seed recovery is still poorly understood. Here, we analyze the factors controlling seed recovery by scatter‐hoarding rodents in an oak‐dominated temperate forest. We examined the relative importance of intrinsic seed traits (i.e. plant‐driven) and extrinsic seed factors (i.e. animal‐driven) on the probability of seed recovery. We found that seed recovery is mainly driven by extrinsic seed factors, mostly related to animal behavior (pilfering frequency, microsite preference, predation risk, burial depth and cache size). Important intrinsic traits such as seed size, seed quality and seed‐drop timing were, on average, of lower significance in the probability of seed recovery (2.8‐times less important than extrinsic factors); only seed quality was an important intrinsic trait. On the other hand, larger and nutritionally more valuable seeds showed a removal–recovery tradeoff as they enhance seed removal and hoarding (increasing dispersal quality) but also favour seed recovery (increasing predation). We find that other mechanisms beyond seed traits (e.g. masting) are needed to decrease seed recovery and, thus, increase seed survival. We conclude that, as seed recovery is mostly driven by animal behavioural factors, it substantially differs from other previous stages of the seed dispersal process that are more dependent on seed traits. We argue that seed recovery needs further attention to advance our understanding of the ecology of seed dispersal and the role of secondary dispersers as a selective force for seeds.     

When condition trumps location: seed consumption by fruit‐eating birds removes pathogens and predator attractants

Seed ingestion by frugivorous vertebrates commonly benefits plants by moving seeds to locations with fewer predators and pathogens than under the parent. For plants with high local population densities, however, movement from the parent plant is unlikely to result in ‘escape’ from predators and pathogens. Changes to seed condition caused by gut passage may also provide benefits, yet are rarely evaluated as an alternative. Here, we use a common bird‐dispersed chilli pepper (Capsicum chacoense) to conduct the first experimental comparison of escape‐related benefits to condition‐related benefits of animal‐mediated seed dispersal. Within chilli populations, seeds dispersed far from parent plants gained no advantage from escape alone, but seed consumption by birds increased seed survival by 370% – regardless of dispersal distance – due to removal during gut passage of fungal pathogens and chemical attractants to granivores. These results call into question the pre‐eminence of escape as the primary advantage of dispersal within populations and document two overlooked mechanisms by which frugivores can benefit fruiting plants.     

Seed dispersal and predation in the endemic Atlantic rainforest palm <Emphasis Type="Italic">Astrocaryum aculeatissimum</Emphasis> across a gradient of seed disperser abundance

Tropical forests have been subject to intense hunting of medium and large frugivores that are important in dispersing large-seeded species. It has been hypothesized that in areas with extinction or low abundance of medium and large-bodied animals the density of small rodents may increase. Therefore, this increment in the density of small rodents may compensate for the absence or low abundance of medium and large frugivores on seed removal and seed dispersal. Here, we fill up this gap in the literature by determining if seed removal, seed dispersal, and seed predation by small rodents (spiny rats, Trinomys inheringi and squirrels, Sciurus ingrami) are maintained in defaunated areas. We accessed seed removal, seed dispersal, seed predation, and seedling recruitment of an endemic Atlantic rainforest palm, Astrocaryum aculeatissimum, in a gradient of abundance of agoutis. We found that seed removal, scatter hoarding, and seed predation increase with the abundance of agoutis. In contrast, the proportion of dispersed but non-cached seeds decreased with the abundance of agoutis. We did not find any effect of the abundance of agoutis on seed dispersal distance, but we did find a positive trend on the density of seedlings. We concluded that small rodents do not compensate the low abundance of agoutis on seed removal, scatter hoarding, and seed predation of this palm tree. Moreover, areas in which agoutis are already extinct did not present any seed removal or scatter hoarding, not even by small rodents. This study emphasizes both the importance of agoutis in dispersing seeds of A. aculeatissimum and the collapse in seed dispersal of this palm in areas where agoutis are already extinct.     

Pleistocene megafaunal extinctions and the functional loss of long‐distance seed‐dispersal services

Pleistocene extinctions affected mainly large‐bodied animals, determining the loss or changes in numerous ecological functions. Evidence points to a central role of many extinct megafauna herbivores as seed dispersers. An important step in understanding the legacy of extinct mutualistic interactions is to evaluate the roles and effectiveness of megafauna herbivores in seed dispersal. Here we use morphological and ecophysiological allometries to estimate both quantitative and qualitative aspects of seed‐dispersal services likely provided by extinct megafauna. We developed a mechanistic model that encompasses four stages of seed dispersal – seed ingestion, gut retention, animal movement, and seed deposition. We estimate seed‐dispersal kernels through simulations to infer the role of Pleistocene megafauna in promoting long‐distance dispersal and examine how seed dispersal was affected by extinctions. Simulations suggest extinct large‐bodied frugivores would frequently disperse large seeds over a thousand meters, whereas smaller‐bodied frugivores are more likely to deposit the seeds over a few hundred meters. Moreover, events of long‐distance seed dispersal by the extinct megafauna would be up to ten times longer than long‐distance dispersal by smaller‐sized extant mammals. By estimating the combined distribution of seed dispersal distances considering all large‐bodied mammalian frugivores in specific South American Pleistocene assemblages we found that long‐distance dispersal contracted by at least two thirds after the megafauna died out. The disruption of long‐distance dispersal is expected to have consequences for recruitment, spatial and genetic structure of plant populations, population persistence and community composition. Promoting long‐distance seed dispersal was one among other salient features of extinct Pleistocene megafauna that reveal their influence on natural ecosystems. Modeling the consequences of megafaunal extinctions can offer quantitative predictions on the consequences of ongoing defaunation to plant populations and ecological communities.     

Integrating frugivory and animal movement: a review of the evidence and implications for scaling seed dispersal

General principles about the consequences of seed dispersal by animals for the structure and dynamics of plant populations and communities remain elusive. This is in part because seed deposition patterns emerge from interactions between frugivore behaviour and the distribution of food resources, both of which can vary over space and time. Here we advocate a frugivore‐centred, process‐based, synthetic approach to seed dispersal research that integrates seed dispersal ecology and animal movement across multiple spatio‐temporal scales. To guide this synthesis, we survey existing literature using paradigms from seed dispersal and animal movement. Specifically, studies are discussed with respect to five criteria: selection of focal organisms (animal or plant); measurement of animal movement; characterization of seed shadow; animal, plant and environmental factors included in the study; and scales of the study. Most studies focused on either frugivores or plants and characterized seed shadows directly by combining gut retention time with animal movement data or indirectly by conducting maternity analysis of seeds. Although organismal traits and environmental factors were often measured, they were seldom used to characterize seed shadows. Multi‐scale analyses were rare, with seed shadows mostly characterized at fine spatial scales, over single fruiting seasons, and for individual dispersers. Novel animal‐ and seed‐tracking technologies, remote environmental monitoring tools, and advances in analytical methods can enable effective implementation of a hierarchical mechanistic approach to the study of seed dispersal. This kind of mechanistic approach will provide novel insights regarding the complex interplay between the factors that modulate animal behaviour and subsequently influence seed dispersal patterns across spatial and temporal scales.     

Hyper-dispersed cache distributions reduce pilferage: a laboratory study

Many animals use hoarding as a long-term strategy to ensure a food supply at times of shortage. We suggest that long-term scatter hoarders, whose caches are vulnerable to potentially high pilferage, should hoard in ways to reduce cache loss. This could be achieved by manipulating the density and dispersal patterns of caches to reduce the foraging efficiency of pilferers. This study explores the effect of distribution patterns on cache loss in the laboratory. We recorded the discovery of food items in different dispersal patterns by two bird species: coal tits Periparus ater (a hoarder) and great tits Parus major (a non-hoarder). Hyper-dispersed distributions reduced foraging efficiency because both species used systematic local search patterns. This study shows that hyper-dispersed distributions would be advantageous to hoarding animals to reduce cache loss.     

Evidence of Social Influences on Cache‐Making by Grey Squirrels (Sciurus carolinensis)

Many studies have found that scatter‐hoarding animals change their behaviour when storing food in the presence of conspecifics to minimize the likelihood that their caches will be pilfered; they refrain from caching, move away from conspecifics or choose visually obscured sites. This study reports the first evidence that the presence of conspecifics continues to influence the caching behaviour of a scatter‐hoarding mammal, the grey squirrel, after a suitable cache site has been selected and the hoarder is filling and covering its cache. Wild grey squirrels were filmed when storing preferred and less preferred nuts and when they were alone or with conspecifics present. In line with previous findings, squirrels spent longer travelling from the nut patch and were more vigilant when conspecifics were present. However, squirrels also spent longer disguising their caches and were more likely to stop digging and become vigilant when conspecifics were present than when they were alone. In particular, they were most likely to curtail their digging when storing their preferred nuts in the presence of conspecifics. The results indicate that caching squirrels remain sensitive to the presence of conspecifics until the cache is complete and that they respond flexibly to conspecifics according to the type of food they are storing.     

Mating Behavior Drives Seed Dispersal by the Long‐wattled Umbrellabird Cephalopterus penduliger

Frugivores exhibit considerable variation in the seed dispersal services they provide. Understanding what drives these differences is a key goal for ecologists because of the central role seed dispersal plays in shaping ecological and genetic diversity in plant populations. The lek‐mating system of the Long‐wattled Umbrellabird (Cephalopterus penduliger) provides a powerful lens to examine how mating behavior may impact seed dispersal outcomes. As in all lek‐breeding species, male Umbrellabirds congregate in traditional sites (leks) to display, whereas females are solitary and visit leks only rarely. This study demonstrates how differences in mating behavior between the sexes drive distinctive seed movement and deposition patterns by male vs. female Umbrellabirds. Using radio tracking and gut retention trials, we documented divergent movement patterns between the sexes that are directly attributable to mating behavior differences. These movement differences led males to disperse seeds long distances from source trees and to deposit the majority of seeds they ingested within the lek; females dispersed seeds shorter distances and more evenly across the landscape. We empirically confirmed that the density of dispersed seeds was higher in leks than in control areas outside the lek, yet found no evidence that this higher density of seeds in leks reduced probability of seedling establishment. This research not only provides a mechanistic explanation for long dispersal distances and high levels of genetic diversity previously reported for seeds in Umbrellabird leks, but also highlights the importance of explicitly considering behavior in studies of animal‐mediated seed dispersal.     

Dissecting the decision making process of scatter‐hoarding rodents

Many animals scatter‐hoard seeds to ensure an even supply of food throughout the year and this behavior requires similar foraging decisions. Seed‐traits have been shown to affect the final foraging decision but little is known about the decision process itself. Here, we first defined four sequential steps comprising the decision process of scatter‐hoarding rodents: 1) upon encountering a seed, should it be ignored or manipulated; 2) if manipulated, should it be eaten in situ or removed elsewhere; 3) upon removal, how far away should it be carried; and finally 4) whether to eat or cache the removed seed. Using experimental seeds with controlled differences in size, tannin and nutrient content, we evaluated how different traits influence each step in this decision process. We found that different traits had distinct effects on each step. Seed size affected all four steps, while nutrient and tannin content primarily affected the first and third steps. By dissecting foraging behavior in relation to experimentally controlled seed‐traits, we have created an effective framework within which to understand the unique relationship between scatter‐hoarding rodents that both predate and disperse plant seeds.     

Role of small rodents in the seed dispersal process: Microcavia australis consuming Prosopis flexuosa fruits

Understanding the functional role of animal species in seed dispersal is central to determining how biotic interactions could be affected by anthropogenic drivers. In the Monte Desert, mammals play different functional roles in Prosopis flexuosa seed dispersal, acting as opportunistic frugivores (endozoochorous medium‐sized and large mammals) or seed hoarders (some small sigmodontine rodents). Our objective was assessing the functional role of Microcavia australis, a small hystricognathi rodent, in the fruit removal and seed deposition stages of P. flexuosa seed dispersal, compared to sympatric sigmodontine rodents. In situ, we quantified fruit removal by small rodents during non‐fruiting and fruiting periods, and determined the distance seeds were transported, particularly by M. australis. In laboratory experiments, we analysed how M. australis stores seeds (through scatter‐ or larder‐hoarding) and how many seeds are left in caches as living seeds, relative to previous data on sigmodontine rodents. To conduct field studies, we established sampling stations under randomly chosen P. flexuosa trees at the Ñacuñán Man and Biosphere Reserve. We analysed fruit removal by small rodents and seed dispersal distance by M. australis using camera traps focused on P. flexuosa fruits covered with wire screen, which only allowed entry of small animals. In laboratory trials, we provided animals with a known number of fruits and assessed seed conditions after removal. Small rodents removed 75.7% of fruit supplied during the non‐fruiting period and 53.2% during the fruiting period. Microcavia australis and Graomys griseoflavus were the main fruit removers. Microcavia australis transported seeds to a mean distance of 462 cm and cached seeds mainly in scatter‐hoards, similarly as Eligmodontia typus. All transported seeds were left in fruit segments or covered only by the endocarp, never as predated seeds. Microcavia australis disperses P. flexuosa seeds by carrying fruits away from a source to consume them and then by scatter‐hoarding fruits and seeds.     

Implications of nonrandom seed abscission and global stilling for migration of wind‐dispersed plant species

Migration of plant populations is a potential survival response to climate change that depends critically on seed dispersal. Biological and physical factors determine dispersal and migration of wind‐dispersed species. Recent field and wind tunnel studies demonstrate biological adaptations that bias seed release toward conditions of higher wind velocity, promoting longer dispersal distances and faster migration. However, another suite of international studies also recently highlighted a global decrease in near‐surface wind speeds, or ‘global stilling’. This study assessed the implications of both factors on potential plant population migration rates, using a mechanistic modeling framework. Nonrandom abscission was investigated using models of three seed release mechanisms: (i) a simple drag model; (ii) a seed deflection model; and (iii) a ‘wear and tear’ model. The models generated a single functional relationship between the frequency of seed release and statistics of the near‐surface wind environment, independent of the abscission mechanism. An Inertial‐Particle, Coupled Eulerian‐Lagrangian Closure model (IP‐CELC) was used to investigate abscission effects on seed dispersal kernels and plant population migration rates under contemporary and potential future wind conditions (based on reported global stilling trends). The results confirm that nonrandom seed abscission increased dispersal distances, particularly for light seeds. The increases were mitigated by two physical feedbacks: (i) although nonrandom abscission increased the initial acceleration of seeds from rest, the sensitivity of the seed dispersal to this initial condition declined as the wind speed increased; and (ii) while nonrandom abscission increased the mean dispersal length, it reduced the kurtosis of seasonal dispersal kernels, and thus the chance of long‐distance dispersal. Wind stilling greatly reduced the modeled migration rates under biased seed release conditions. Thus, species that require high wind velocities for seed abscission could experience threshold‐like reductions in dispersal and migration potential if near‐surface wind speeds continue to decline.     

The mismatch in distributions of vertebrates and the plants that they disperse

Little is known about how mutualistic interactions affect the distribution of species richness on broad geographic scales. Because mutualism positively affects the fitness of all species involved in the interaction, one hypothesis is that the richness of species involved should be positively correlated across their range, especially for obligate relationships. Alternatively, if mutualisms involve multiple mutualistic partners, the distribution of mutualists should not necessarily be related, and patterns in species distributions might be more strongly correlated with environmental factors. In this study, we compared the distributions of plants and vertebrate animals involved in seed‐dispersal mutualisms across the United States and Canada. We compiled geographic distributions of plants dispersed by frugivores and scatter‐hoarding animals, and compared their distribution of richness to the distribution in disperser richness. We found that the distribution of animal dispersers shows a negative relationship to the distribution of the plants that they disperse, and this is true whether the plants dispersed by frugivores or scatter‐hoarders are considered separately or combined. In fact, the mismatch in species richness between plants and the animals that disperse their seeds is dramatic, with plants species richness greatest in the in the eastern United States and the animal species richness greatest in the southwest United States. Environmental factors were corelated with the difference in the distribution of plants and their animal mutualists and likely are more important in the distribution of both plants and animals. This study is the first to describe the broad‐scale distribution of seed‐dispersing vertebrates and compare the distributions to the plants they disperse. With these data, we can now identify locations that warrant further study to understand the factors that influence the distribution of the plants and animals involved in these mutualisms.     

Species traits and interaction rules shape a species‐rich seed‐dispersal interaction network

Species phenotypic traits affect the interaction patterns and the organization of seed‐dispersal interaction networks. Understanding the relationship between species characteristics and network structure help us understand the assembly of natural communities and how communities function. Here, we examine how species traits may affect the rules leading to patterns of interaction among plants and fruit‐eating vertebrates. We study a species‐rich seed‐dispersal system using a model selection approach to examine whether the rules underlying network structure are driven by constraints in fruit resource exploitation, by preferential consumption of fruits by the frugivores, or by a combination of both. We performed analyses for the whole system and for bird and mammal assemblages separately, and identified the animal and plant characteristics shaping interaction rules. The structure of the analyzed interaction network was better explained by constraints in resource exploitation in the case of birds and by preferential consumption of fruits with specific traits for mammals. These contrasting results when looking at bird–plant and mammal–plant interactions suggest that the same type of interaction is organized by different processes depending on the assemblage we focus on. Size‐related restrictions of the interacting species (both for mammals and birds) were the most important factors driving the interaction rules. Our results suggest that the structure of seed‐dispersal interaction networks can be explained using species traits and interaction rules related to simple ecological mechanisms.     

Incorporating seed fate into plant–frugivore networks increases interaction diversity across plant regeneration stages

Plant–animal mutualistic interactions, such as pollination and seed dispersal, affect ecosystem functioning by driving plant population dynamics. However, little is known of how the diversity of interactions in these mutualistic networks determines plant regeneration dynamics. To fill this gap, interaction networks should not only account for the number of seeds dispersed by animals, but also for seed fate after dispersal. Here, we compare plant–animal networks at both the seed dispersal and seedling recruitment stage to evaluate how interaction diversity, represented by different network metrics, changes throughout the process of plant regeneration. We focused on a system with six species of frugivorous birds and three species of fleshy‐fruited trees in the temperate secondary forest of the Cantabrian Range (northern Iberian Peninsula). We considered two plant cohorts corresponding to two fruiting years showing strong differences in fruit and frugivore abundance. Seed dispersal interactions were estimated from a spatially‐explicit, field‐validated model predicting tree and bird species‐specific seed deposition in different microhabitats. These interactions were further transformed into interactions at the seedling recruitment stage by accounting for plant‐ and microhabitat‐specific seed fates estimated from field sampling. We found that network interaction diversity varied across plant regeneration stages and cohorts, both in terms of the evenness and the number of paired interactions. Tree–bird interactions were more evenly distributed across species pairs at the recruitment stage than at the seed deposition stage, although some interactions disappeared in the seed‐to‐seedling transition for one plant cohort. The variations in interaction diversity were explained by between‐plant differences in post‐dispersal seed fate and in inter‐annual fruit production, rather than by differences between frugivores in seed deposition patterns. These results highlight the need for integrating plant traits and disperser quality to predict the functional outcome of plant–animal mutualistic networks.     

The evolution of hippocampus volume and brain size in relation to food hoarding in birds

Food‐hoarding birds frequently use spatial memory to relocate their caches, thus they may evolve a larger hippocampus in their brain than non‐hoarder species. However, previous studies testing for such interspecific relationships provided conflicting results. In addition, food hoarding may be a cognitively complex task involving elaboration of a variety of brain regions, even outside of the hippocampus. Hence, specialization to food hoarding may also result in the enlargement of the overall brain. In a phylogenetic analysis of distantly related birds, we studied the interspecific association between food hoarding and the size of different brain regions, each reflecting different resolutions. After adjusting for allometric effects, the relative volume of the hippocampus and the relative size of the entire brain were each positively related to the degree of food‐hoarding specialization, even after controlling for migration and brood parasitism. We also found some significant evidence for the relative volume of the telencephalon being associated with food hoarding, but this relationship was dependent on the approach we used. Hence, neural adaptation to food hoarding may favour the evolution of different brain structures.     

Forest cover,hunting pressure,and fruit availability influence seed dispersal in a forest‐savanna mosaic in the Congo Basin

Forest fragmentation, reduced forest cover, and hunting pressure are the main threats affecting animal‐mediated seed dispersal. However, their combined effects on seed dispersal rates have been simultaneously investigated only rarely, and never in Africa. We aimed to disentangle the effects of forest cover, hunting pressure, frugivore abundance, and fruit availability at the local and landscape scales on the seed dispersal rates of Staudtia kamerunensis (Myristicaceae). To estimate the percentages of seed dispersal failure (undispersed seeds), we quantitated fruit remains below fruiting trees distributed across five contrasting sites in a semi‐natural forest‐savanna mosaic in the Democratic Republic of Congo. We used statistical analyses accounting for spatial autocorrelation and found that forest cover in the surrounding landscape, hunting level, the associated abundance of dispersers, and fruit availability all had significant effects on the percentage of seed dispersal failure. The combination of high fruit availability and reduced abundance of seed dispersers could accelerate seed disperser satiation, causing the seed dispersal system to be saturated. Our study highlights how two major factors associated with anthropogenic activities, forest cover and hunting, affect seed dispersal by animals. These findings could have far‐reaching implications for our understanding of tree‐frugivore interactions and the conservation of tropical communities.