New Publication on Red Kite conservation!

Sergio, F, Tavecchia, G., Blas, J., Taferna, A., Hiraldo, F.  2021. Demographic modeling to fine‐tune conservation targets: importance of pre‐adults for the decline of an endangered raptor. Ecological Applications, https://doi.org/10.1002/eap.2266

Summary: Large, long‐lived species with slow life histories and protracted pre‐breeding stages are particularly susceptible to declines and extinction, often for unknown causes. Here, we show how demographic modeling of a medium‐sized raptor, the Red Kite Milvus milvus, can aid to refocus conservation research and attention on the most likely mechanisms driving its decline. Red Kites’ survival and reproduction increased through three sequential stages for 1–2, 3–6, and 7–30 yr of age, mainly corresponding to individuals that are dispersing, attempting to gain a territory, and breeding. As typical of long‐lived species, elasticities were highest for adult (≥7 yr old) survival, but this was high, with little scope for improvement. Instead, the declines were driven by an extremely low survival of pre‐adults in their first years of life, which weakened the whole demographic system by nullifying the offspring contribution of adults and curtailing their replacement by recruits. For example, 27 pairs were necessary to generate a single prime age adult. Simulation of management scenarios suggested that the decline could be halted most parsimoniously by increasing pre‐adult survival to the mean levels recorded for other areas, while only the synergistic, simultaneous improvement of breeding success, adult and pre‐adult survival could generate a recovery. We propose three actions to attain such goals through selective supplementary feeding of both breeding and non‐breeding individuals, and through mortality improvement by GPS remote‐sensing devices employed as surveillance monitoring tools. Our results show how improving demographic models by using real, local vital rates rather than “best guess” vital rates can dramatically improve model realism by refocusing attention on the actual stages and mortality causes in need of manipulation, thus building precious time and resources for conservation management. These results also highlight the frequent key role of pre‐adult survival for the management of long‐lived species, coherent with the idea of demographic systems as integrated chains only as strong as their weakest link.

 

 

 

New Publication on mate-finding in tortoises!

Jiménez-Franco, M.V., Giménez, A., Rodgríguez-Caro, R.C., Sanz-Aguilar, A., Botella, F., Anadón, J.D., Wiegand, T., Graciá, E. 2020. Sperm storage reduces the strength of the mate-finding Allee effect. Ecology and Evolution, https://doi.org/10.1002/ece3.6019
 
Abstract: Mate searching is a key component of sexual reproduction that can have important implications for population viability, especially for the mate‐finding Allee effect. Interannual sperm storage by females may be an adaptation that potentially attenuates mate limitation, but the demographic consequences of this functional trait have not been studied. Our goal is to assess the effect of female sperm storage durability on the strength of the mate‐finding Allee effect and the viability of populations subject to low population density and habitat alteration. We used an individual‐based simulation model that incorporates realistic representations of the demographic and spatial processes of our model species, the spur‐thighed tortoise (Testudo graeca).

Photo: wikipedia.org

This allowed for a detailed assessment of reproductive rates, population growth rates, and extinction probabilities. We also studied the relationship between the number of reproductive males and the reproductive rates for scenarios combining different levels of sperm storage durability, initial population density, and landscape alteration. Our results showed that simulated populations parameterized with the field‐observed demographic rates collapsed for short sperm storage durability, but were viable for a durability of one year or longer. In contrast, the simulated populations with a low initial density were only viable in human‐altered landscapes for sperm storage durability of 4 years. We find that sperm storage is an effective mechanism that can reduce the strength of the mate‐finding Allee effect and contribute to the persistence of low‐density populations. Our study highlights the key role of sperm storage in the dynamics of species with limited movement ability to facilitate reproduction in patchy landscapes or during population expansion. This study represents the first quantification of the effect of sperm storage durability on population dynamics in different landscapes and population scenarios.