Environmental conditions modulate compensatory effects of site dependence in a food‐caching passerine

Abstract

Although density regulates the abundance of most wild animal populations by influencing vital rates, such as fecundity and survival, the mechanisms responsible for generating negative density dependence are unclear for many species. Site dependence occurs when there is preferential filling of high‐quality territories, which results in higher per capita vital rates at low densities because a larger proportion of occupied territories are of high quality. Using 41 yr of territory occupancy and demographic data, we investigated whether site dependence was a mechanism acting to influence fecundity and, by extension, regulate a population of Canada Jays in Algonquin Provincial Park, Ontario, Canada. As predicted by site dependence, the proportion of occupied territories that were of high quality was negatively correlated with population density and periods of vacancy were shorter for high‐quality territories than for low‐quality territories. We also found evidence that per capita fecundity was positively related to the proportion of occupied territories that were of high quality, but only when environmental conditions, which influence the entire population, were otherwise poor for breeding. Our results suggest that site dependence likely plays a role in regulating this population but that environmental conditions can modulate the strength of density dependence.

Climate‐driven carry‐over effects negatively influence population growth rate in a food‐caching boreal passerine

“…Second, a prior analysis showed that adults and juveniles tend to more frequently disperse away from low‐quality territories compared to high‐quality territories (Norris et al., 2013) and many of the territories in the core study area were of low quality. Consequently, as these territories became vacant over the course of the study, they would be less likely to be reoccupied (Sutton et al, 2020). Furthermore, climate change may have reduced the quality of all territories within the core and peripheral study areas and this may have resulted in biased northward dispersal away from the southern edge of the Canada jay's range.…”

“…Second, a prior analysis showed that adults and juveniles tend to more frequently disperse away from low-quality territories compared to high-quality territories (Norris et al, 2013) and many of the territories in the core study area were of low quality. Consequently, as these territories became vacant over the course of the study, they would be less likely to be reoccupied (Sutton et al, 2020). under future warming scenarios (Ridgeway et al, 2018), it is more likely that we will see the local extirpation of Canada jays from Algonquin Provincial Park and other southern range-edge populations.…”

Breeding dispersal in a resident boreal passerine can lead to short‐ and long‐term fitness benefits

“…Of course, for breeding dispersal to be a factor at the population level, the improvement in individual reproductive success would have to be strong enough to affect population growth rates. This could be the case in some declining populations of other species where breeding dispersal has been shown to be beneficial at the individual level (Palestis andHines 2015, Williams andBoyle 2019), but it is probably unlikely in Canada jays given their relatively low annual reproductive output (Sutton et al 2021b). Breeding dispersal acting as a mechanism for negative density-dependence would also rest on the assumption that most dispersal at low densities would occur within the population (i.e., short distances).…”

Early-life sibling conflict in Canada jays has lifetime fitness consequences

“…We estimated inclusive fitness of DJs and EJs in a resident population of Canada jays in Algonquin Provincial Park (APP), Ontario, Canada (45° N, 78° W; 760 000 ha) that has been monitored along the Highway 60 corridor from 1964 to 2022 [28]. In the late summer and early fall, APP Canada jays begin to scatter-hoard perishable food items under tree bark or lichens, which they rely on for over-winter survival and nesting beginning in the late winter [18].…”

“…To determine whether ARS (defined by the mean total recruits) differed between DJs and EJs, we ran a series of generalized linear models (GLMs, Poisson distribution, log link function) with total number of recruits per individual as the response variable and social status (DJ or EJ), sex (determined with molecular methods; [24]), and maximum known age (oldest confirmed age of an individual before disappearance) as fixed effects. Due to limited sample size, we could not include environmental variables known to influence reproductive performance as predictors [28,29]. We then took the mean number of recruits for each juvenile class from the raw long-term data to estimate o .…”