The distance and quality of seed dispersal may vary with social status
Social status predictably impacts individual space use such that social status may be used to predict the distance and quality of seed dispersal, specifically characteristics of deposition sites which affect the probability of post-dispersal predation and seedling establishment (e.g., suitable microsite availability and abundance of natural enemies: Schupp 1993; Schupp et al. 2010). In systems where a resource can be monopolized (e.g., fruiting trees), the defense of resources by dominant individuals can create situations where subordinates steal defended resources and then move far away to avoid antagonistic encounters, thereby elongating seed-dispersal kernels (Box 2, Fig. 2A). The contrast in space use between resource-defending dominant individuals and resource-stealing subordinates has been explicitly linked to patterns in seed dispersal in a study of flying foxes (McConkey & Drake 2006). However, thieving behaviors by subordinates have been documented in a variety of taxa, including birds, primates, and bats (Sallabanks 1993; McConkey & Drake 2006; Ward & Webster 2016b; Tsuji et al.2020), indicating that this is a potentially profitable, yet largely untapped area of research that may elucidate patterns in seed-dispersal kernels.
For group-living large mammals, an individual’s rank within a dominance hierarchy has well-documented effects on its movement across landscapes. Dominant individuals often have more restricted home ranges, spending more time in predictable, preferred habitat types (Aycrigg & Porter 1997; Henry et al. 2005; Wittemyer et al. 2007; Dorning & Harris 2017; Kamler et al. 2019). Subordinate individuals often forego foraging efficiency to mitigate competition with dominants (Henryet al. 2005; Gilbert-Norton et al. 2013; Dorning & Harris 2017), and this increased movement likely leads to an increase in the diversity of habitats in which seeds may be deposited as well as increased dispersal distance (Fig. 1). Broader distinctions between territorial and transient individuals may also be used to predict spatial patterns in seed dispersal and recruitment. For example, territorial males in lekking blackbuck antelope (Antilope cervicapra ) populations defecate in dung piles, leading to spatially concentrated patterns of seed arrival within male territories and substantially higher rates of seedling recruitment on territories than on random sites (Jadeja et al. 2013). Since non-territorial males in mixed-sex herds range over large areas and do not predictably deposit seeds in dung piles, seed dispersal by non-territorial individuals is likely lower in quality. This example highlights that commonly used methods for estimating seed dispersal that rely upon individual movement patterns and gut-retention time may not accurately capture intraspecific variation in dispersal efficacy if the quality of deposition site for plant recruitment is not also evaluated. Since individual movement and habitat use is affected by social status, the quality of seed-deposition sites may vary among individuals of different social statuses (Fig. 1). Studies that not only estimate seed dispersal but also measure post-dispersal seed fate (i.e., seed predation and recruitment) at deposition sites will provide greater clarity on how the quality of seed dispersal varies between individuals of different social statuses. For example, past work shows that seed deposition in coyote scat increases seed survival for rodent-preferred seeds but decreases seed survival for arthropod-preferred seeds due to the contrasting effects of mesopredator scat on rodents (aversion) and arthropods (attraction; Bartel and Orrock 2021). Hence, if dominant individuals deposit seeds in microhabitats with different granivore communities than the microhabitats in which subordinates deposit seeds, then the probability of post-dispersal seed survival may drastically differ. This contrast may be most evident in group-living canids, like coyotes, where dominant individuals spend more time maintaining territory boundaries, often through scent-marking and scat deposition, than subordinate individuals (Gese 2001). Since territory boundaries often fall along habitat edges, including roads and trails, seed fate may differ among dominant- and subordinate-dispersed seeds if granivores either avoid or prefer edges.
An individual’s efficacy as a seed-dispersal agent may change over its lifetime if social status changes over a lifetime. For example, social dominance in grizzly bear (Ursus arctos horribilis ) populations is typically a result of individual size (larger bears are dominant over smaller bears) and reproductive status (females with cubs are subordinate to single males; Ben-David et al. 2004; Gende and Quinn 2004). Since individual social status affects bear diet and space use (Box 1), juvenile males are likely to become less effective seed-dispersal agents over their lifetime, and females are likely to be most effective seed-dispersal agents during their lifetime when they are rearing cubs. The capacity for an individual’s efficacy as a seed-dispersal agent to rapidly change raises a clear distinction between the effects of social status and personality on seed dispersal. While definitions of animal personalities are often context- or system-specific, personality is most broadly defined as individual differences in behavior that are consistent across time and/or contexts (Dall et al. 2004; Stamps & Groothuis 2010). In contrast, an individual’s social status has the capacity to change across time or context, particularly as a result of changes in the individual’s social environment. While individual personality traits can sometimes be correlated with social dominance (Briffa et al. 2015), personality and social dominance are not related in many animal societies (Favati et al. 2013; Funghi et al. 2015; Devostet al. 2016). Dominance is the product of myriad environmental factors (e.g., relative size, relative age, reproductive status, maternal rank, social alliances; Favati et al. 2013; Funghi et al. 2015; Devost et al. 2016; Strauss and Holekamp 2019; Ilany et al. 2021), but personality is by definition consistent across time and context, though it may develop in response to individual experience (Stamps & Groothuis 2010). Hence, individual behaviors that are a result of personality should remain consistent over short timespans, but any changes to an individual’s social environment that lead to a rapid change in social status are expected to rapidly change individual behavior and efficacy as a seed-dispersal agent.