Are there ecological consequences of vanishing proactive
phenotypes?
Many studies have noted the essential role of keystone species that
warrant specific conservation efforts due to their central position for
the functioning of a community (Mills et al. 1993; Paine 1995;
Betts et al. 2015), and whose extinction or massive population
decline could have massive consequences on community structure
(Cortés-Avizanda et al. 2015). Recent work has focused on the
essential role played by some individuals in a group and coined the term
keystone individuals (Modlmeier et al. 2014; Pruitt & Keiser
2014). Modelmeier et al. (2014: p55) defined these individuals as having
“a disproportionally large, irreplaceable effect on other group members
and/or the overall group dynamics relative to its abundance”.
The vanishing of proactive phenotypes could first have consequence in
terms of group composition and population dynamics as these individuals
are likely to be keystone individuals. As noted above, proactive
individuals tend to disperse more, while reactive individuals are more
likely to join newly colonized areas (Cote et al. 2010a). If new
populations are composed only from reactive individuals, this may
constrain dispersal and space use. For instance, group mean personality
scores (boldness, activity, and sociability) of some feral guppy
(Poecilia reticulata ) populations was not associated with
exploratory propensity. Rather, group exploratory propensity was driven
by the personality of key individuals whereby slow individuals tended to
slow down exploration rates of the shoal (Brown & Irving 2014). In
mosquitofish (Gambusia affinis ) mean group personality appeared
to also drove group dispersion patterns in the expected pattern (group
with many asocial individuals disperse further) although there were no
keystone individuals identified (Cote et al. 2010b). Because
exploration is likely associated with resource harvesting patterns, we
can envision that HIREC may modify these patterns and have consequences
at other trophic levels. Thus, if a system evolved with a mix of shy and
bold individuals, and HIREC systematically eliminated one type, we
should expect changes in species composition.
The disappearance of one phenotype could also have substantial
consequences on prey-predator relationships. In a recent review, it was
considered that a proactive or a reactive response of a prey largely
depends on the predictability of an encounter with a predator (Creel
2018). The former response will have an energetic cost (fleeing) while
the latter would have stress-mediated cost, by activating the HPI/A axis
(Creel 2018). However, this approach largely ignored intrinsic
differences in coping abilities between individuals of the same species
and rather considered that all individuals are able to mount a similar
response according to the situation. Here we suggest that the type of
response would also depend on the personality of each individual,
although ecological consequences would be the same. If proactive
individuals vanish from the population, then responses to a predator
consisting of displaying aggressive behavior, modifying activity
periods, or engaging in particular patterns of vigilance (Creel 2018)
would likely be quite different. Rather, the reactive response will be
systematically produced, with all its associated stress-related costs.
For instance, in the snowshoe hare-lynx system, predation risk increased
glucocorticoid production with direct consequences in the decline of
offspring production (Krebs et al. 1995). Hence, we can expect
that always mounting a reactive response to predatory encounters would
lead to chronic stress and its associated consequences in terms of
reproductive success.
We know that behavioral variation is an index of genetic variation
(Smith & Blumstein 2013). If we selectively reduce phenotypic
variation, we are likely reducing genotypic variation. Such a reduction
may be ultimately costly if it reduces a population’s adaptive potential
to what may ultimately be a more variable environment. This loss of
behavioral diversity may be particularly acute in conservation
management when animals are brought into captivity for breeding with
subsequently planned translocations and reintroductions (e.g., Smith &
Blumstein 2012; Merrick & Koprowski 2017). We expect captivity to
reduce genetic variation and also to eliminate the very variation that
may be essential for the wild.