martes, 20 de octubre de 2015

New publication on foraging range and colony size in seabirds

Jovani, R,; Lascells, B.; Garamszegi, L. Z.; Mavor, R.; Oro, D.Colony size and foraging range in seabirds. Oikos DOI: 10.1111/oik.02781

We tested “Ashmole’s halo” hypothesis of food depletion around colonies using a phylogenetic comparative study of 43 species of seabirds (28,262 colonies). We confirmed that foraging range imposes a ceiling on the maximum colony size of seabird species. 

Abstract:The reasons for variation in group size among animal species remain poorly understood. Using “Ashmole's halo” hypothesis of food depletion around colonies, we predict that foraging range imposes a ceiling on the maximum colony size of seabird species. We tested this with a phylogenetic comparative study of 43 species of seabirds (28,262 colonies), and investigated the interspecific correlation between colony size and foraging ranges. Foraging range showed weak relationships with the low percentiles of colony size of species, but the strength of the association increased for larger percentiles, peaking at the maximum colony sizes. To model constraints on the functional relationship between the focal traits, we applied a quantile regression based on maximum colony size. This showed that foraging range imposes a constraint to species' maximum colony sizes with a slope around 2. This second-order relationship is expected from the equation of the area of a circle. Thus, our large dataset and innovative statistical approach shows that foraging range imposes a ceiling on seabird colony sizes, providing strong support to the hypothesis that food availability is an important regulator of seabird populations.
You can read the philosophy behind “Colony size and foraging range in seabirds” in Oikos blog, by Roger Jovani

lunes, 19 de octubre de 2015

New publication on spring population dynamics of lizards

Pérez-Mellado, V., Garcia-Diez, T., Hernández-Estévez, J.A. & Tavecchia, G. : Behavioural processes, ephemeral resources and spring population dynamics of an insular lizard, Podarcis lilfordi (Squamata: Lacertidae). Italian Journal of Zoology doi: 10.1080/11250003.2015.1093035

Abstract: Temporal changes in adult sex ratio of animal populations might be due to differences in movements, survival or detection probabilities. We used data from an intensive capture–mark–recapture study of 720 lizards at the islet of Aire (Balearic Islands, Spain) to investigate the demographic mechanisms underlying the spring uneven sex ratio. We simultaneously estimated survival (f), the proportion of transient animals (p) and the probability of recapture (p) of lizards at the study plot.
Photo: G. Tavecchia
We then estimated population size using open population models for individually based data and compared these with the observed values. Results indicated that males had a higher probability of recapture than females, but this was not sufficient to generate the observed male-biased sex ratio. The proportion of transient males decreased at the end of spring in parallel with the end of the blooming period of the dead horse arum, Helicodiceros muscivorus, a short-lasting food and thermoregulation resource for lizards during spring. Changes in the proportion of transients suggested that sex-dependent movements, most likely linked to a monopolising behaviour of this plant resource, were responsible for the observed difference in the number of males and females. Our results reveal how the interplay of behavioural and ecological factors explains short-term changes in population dynamics and shapes the movement patterns within the island.

viernes, 9 de octubre de 2015

Lizard October Campaign just started !!

The October campaign on capture-recapture of lizards just started with two new important discoveries:

1 - The "Imperial Sardines pincho"(c), a slice of bread with sardines on fresh tomatoe sauce, chopped garlic, parsley and Soy sauce. Freshly made and freshly served ! 

2-  The proof of elephant dwarfism on islands (we were not able to find any giant rat, though)

(...and as usual, we came back with quite a lot of rubbish washed on the island).