Browsing by Author "Rotella, Jay"

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Drivers of variation in the population dynamics of bighorn sheep
(Wiley, 2021-07) Paterson, J. Terrill; Proffitt, Kelly M.; Rotella, Jay; McWhirter, Douglas; Garrott, Robert
Understanding how variation in vital rates interact to shape the trajectories of populations has long been understood to be a critical component of informed management and restoration efforts. However, an expanding body of work suggests that the expectations for population dynamics of ungulates may not be applicable to small, declining, or threatened populations. Populations of bighorn sheep (Ovis canadensis) suffered declines at the turn of the 20th century, and restoration efforts have been mixed such that many populations remain small and isolated. Here, we utilized survey data collected from 1983 to 2018 from 17 populations of bighorn sheep in Montana and Wyoming to estimate the parameters of a stage-specific population model that we used to (1) characterize the spatial and temporal variation in key vital rates including whether populations were stable, increasing, or declining; (2) estimate the contributions of vital rates to variation in population growth rates; and (3) evaluate potential sources of variation in lamb survival. We found substantial variation in all vital rates both among years and populations, strong evidence for an overall decline in nine of the 17 populations, and clear evidence for multiple combinations of vital rates that resulted in positive population trajectories. The contribution of ewe survival and lamb survival to the total variation in population growth rates varied among populations; however, declines in ewe survival dominated transitions of population trajectories from stable or increasing to declining, whereas reversals of declining population trajectories were dominated by improved lamb survival. We found strong evidence for a diverse set of associations between lamb survival and environmental covariates related to growing season and winter severity. The estimated relationships predict that environmental drivers can cause important changes in lamb survival and provide suggestive evidence that the presence of Mycoplasma ovipneumoniae is not sufficient to prevent population growth. Although our work demonstrates that the trajectories of these populations of bighorn sheep are driven by a variety of processes, the diversity of relationships between vital rates and population growth rates also suggests that there are multiple pathways to manage for population recovery.
First observations of Weddell seals foraging in sponges in Erebus Bay, Antarctica
(Springer Science and Business Media LLC, 2023-05) Foster-Dyer, Rose T. N.; Goetz, Kimberly T.; Pinkerton, Matthew H.; Iwata, Takashi; Holser, Rachel R.; Michael, Sarah A.; Pritchard, Craig; Childerhouse, Simon; Rotella, Jay; Federwisch, Luisa; Costa, Daniel P.; LaRue, Michelle A.
Attaching cameras to marine mammals allows for first-hand observation of underwater behaviours that may otherwise go unseen. While studying the foraging behaviour of 26 lactating Weddell seals (Leptonychotes weddellii) in Erebus Bay during the austral spring of 2018 and 2019, we witnessed three adults and one pup investigating the cavities of Rossellidae glass sponges, with one seal visibly chewing when she removed her head from the sponge. To our knowledge, this is the first report of such behaviour. While the prey item was not identifiable, some Trematomus fish (a known Weddell seal prey) use glass sponges for shelter and in which to lay their eggs. Three of the four sponge foraging observations occurred around 13:00 (NZDT). Two of the three sponge foraging adults had higher-than-average reproductive rates, and the greatest number of previous pups of any seal in our study population, each having ten pups in 12 years. This is far higher than the study population average of three previous pups (± 2.6 SD). This novel foraging strategy may have evolved in response to changes in prey availability, and could offer an evolutionary advantage to some individuals that exploit prey resources that others may not. Our observations offer new insight into the foraging behaviours of one of the world’s most studied marine mammals. Further research on the social aspects of Weddell seal behaviour may increase our understanding of the extent and mechanisms of behavioural transfer between conspecifics. Research into the specific foraging behaviour of especially successful or experienced breeders is also warranted.
Individual life histories: neither slow nor fast, just diverse
(The Royal Society, 2023-07) Van de Walle, Joanie; Fay, Rémi; Gaillard, Jean-Michel; Pelletier, Fanie; Hamel, Sandra; Gamelon, Marlène; Barbraud, Christophe; Blanchet, F. Guillaume; Blumstein, Daniel T.; Charmantier, Anne; Delord, Karine; Larue, Benjamin; Martin, Julien; Mills, James A.; Milot, Emmanuel; Mayer, Francine M.; Rotella, Jay; Saether, Bernt-Erik; Teplitsky, Céline; van de Pol, Martijn; Van Vuren, Dirk H.; Visser, Marcel E.; Wells, Caitlin P.; Yarrall, John; Jenouvrier, Stéphanie
The slow–fast continuum is a commonly used framework to describe variation in life-history strategies across species. Individual life histories have also been assumed to follow a similar pattern, especially in the pace-of-life syndrome literature. However, whether a slow–fast continuum commonly explains life-history variation among individuals within a population remains unclear. Here, we formally tested for the presence of a slow–fast continuum of life histories both within populations and across species using detailed long-term individual-based demographic data for 17 bird and mammal species with markedly different life histories. We estimated adult lifespan, age at first reproduction, annual breeding frequency, and annual fecundity, and identified the main axes of life-history variation using principal component analyses. Across species, we retrieved the slow–fast continuum as the main axis of life-history variation. However, within populations, the patterns of individual life-history variation did not align with a slow–fast continuum in any species. Thus, a continuum ranking individuals from slow to fast living is unlikely to shape individual differences in life histories within populations. Rather, individual life-history variation is likely idiosyncratic across species, potentially because of processes such as stochasticity, density dependence, and individual differences in resource acquisition that affect species differently and generate non-generalizable patterns across species.
Temporal correlations among demographic parameters are ubiquitous but highly variable across species
(Wiley, 2022-07) Fay, Rémi; Hamel, Sandra; van de Pol, Martijn; Gaillard, Jean‐Michel; Yoccoz, Nigel G.; Acker, Paul; Authier, Matthieu; Larue, Benjamin; Coeur, Christie Le; Macdonald, Kaitlin R.; Nicol‐Harper, Alex; Barbraud, Christophe; Bonenfant, Christophe; Van Vuren, Dirk H.; Cam, Emmanuelle; Delord, Karine; Gamelon, Marlène; Moiron, Maria; Pelletier, Fanie; Rotella, Jay; Teplitsky, Celine; Visser, Marcel E.; Wells, Caitlin P.; Wheelwright, Nathaniel T.; Jenouvrier, Stéphanie; Sæther, Bernt‐Erik
Temporal correlations among demographic parameters can strongly influence population dynamics. Our empirical knowledge, however, is very limited regarding the direction and the magnitude of these correlations and how they vary among demographic parameters and species’ life histories. Here, we use long-term demographic data from 15 bird and mammal species with contrasting pace of life to quantify correlation patterns among five key demographic parameters: juvenile and adult survival, reproductive probability, reproductive success and productivity. Correlations among demographic parameters were ubiquitous, more frequently positive than negative, but strongly differed across species. Correlations did not markedly change along the slow-fast continuum of life histories, suggesting that they were more strongly driven by ecological than evolutionary factors. As positive temporal demographic correlations decrease the mean of the long-run population growth rate, the common practice of ignoring temporal correlations in population models could lead to the underestimation of extinction risks in most species.