New Publication on a Cryptic Cetacean!

Tenan, S., Moulins, A., Tepsich, P., Bocconcelli, A., Verga, A., Ballardini, M., Nani, B., Papi, D., Motta, G., Aguilar, A. S., & Rosso, M. (2023). Immigration as the main driver of population dynamics in a cryptic cetacean. Ecology and Evolution, 13, e9806. https://doi.org/10.1002/ece3.9806

Abstract: Empirical evidence about the role and interaction of immigration with local demographic processes in shaping population dynamics is still scarce. This knowledge gap limits our capability to derive a conceptual framework that can be used to inform conservation actions. Populations exposed to nonstationary environment do not converge to a stable stage distribution, implying the need for evaluating the demographic role of both vital rates and stage distribution using appropriate tools. This is particularly important for species with larger generation times like cetaceans. We explored the relative demographic role of vital rates and population structure of a poorly known cetacean, the Mediterranean Cuvier's beaked whale, while accounting for the exposure to nonstationary environments. 

Photo: N Aguilar

We performed a retrospective analysis through transient life table response experiments (tLTRE) using demographic rates and population structure of both sexes obtained from an integrated population model. The contribution of immigration to variation in realized population growth rates was 4.2, 7.6, and 12.7 times larger than that of female apparent survival, proportional abundance of breeding females with a 2-year-old calf, and proportional abundance of breeding females with a 3-year-old calf, respectively. Immigration rate and proportional abundance of breeding females with a 2- or 3-year-old calf explained, respectively, 65% and 20% of total temporal variability in realized population growth rates. Changes in realized population growth rate between successive years were mainly driven by changes in immigration and population structure, specifically the proportional abundance of breeding females with a 2-year-old calf. Our study provides insight into the demographic processes that affect population dynamics and in a cryptic cetacean. We presented an analytical approach for maximizing the use of available data through the integration of multiple sources of information for individuals of different distinctiveness levels.

New Publication on population dynamics of Audouin's Gull !

Genovart, M., Oro, D. and Tenan, S. 2018. Immature survival, fertility, and density dependence drive global population dynamics in a long‐lived species. Ecology, https://doi.org/10.1002/ecy.2515

Abstract: Disentangling the influence of demographic parameters and the role of density dependence on species’ population dynamics is a challenge, especially when fractions of the population are unobservable. Additionally, due to the difficulty of gathering data at large spatial scales, most studies ignore the global dynamic of a species, which would integrate local heterogeneity dynamics and remove the noise of dispersal. We developed an integrated population model (IPM) at a global scale to disentangle the main demographic drivers of population dynamics in a long‐lived species.

We used 28 yr of Audouin's Gull demographic data encompassing 69 local patches (comprising 90% of the world population). Importantly, we took into account the unobservable fraction of non‐breeders and also assessed the strength of density dependence for this fraction of the population. As predicted by life histories of long‐lived organisms, temporal random variation in survival was highest for immature individuals (1.326, 95% credible interval [CRI] 1.290–1.940) and lowest for adults (0.499, 95% CRI 0.487–0.720). Large temporal fluctuations in the probability of taking a reproductive sabbatical would partly explain the consistency in adult survival, with individuals most likely refraining from breeding when environmental conditions were harsh. Immature survival and fertility were the main drivers of population dynamics during the study period (r² = 0.83, 0.77–0.87 and 0.73, 0.63–0.79, respectively). We found strong evidence of density dependence, not only due to the number of breeders (r² = −0.34, −0.43 to −0.24) but also due to individuals on sabbatical (r² = −0.18, −0.33 to −0.01). From a conservation point of view, the species shows a 5% annual global decrease during the last 10 years, and we propose an update of its conservation status. Even though population dynamics of long‐lived organisms are very sensitive to changes in adult survival, we show here that, in the absence of strong environmental perturbations affecting this vital rate, fluctuations in population density are mainly driven by variations in survival of immature individuals and fertility. Integrated models based on long‐term monitoring at a global scale may enhance our ecological and evolutionary understanding of how demographic drivers influence population dynamics.