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.