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).

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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.

New Publication on individual-based model and extinction!

Graciá, E., Rodríguez-Caro, R., Sanz-Aguilar, A., [...] Giménez, A., 2020. Assessment of the key evolutionary traits that prevent extinctions in human-altered habitats using a spatially explicit individual-based model. Ecological Modelling Vol 415. https://doi.org/10.1016/j.ecolmodel.2019.108823

Abstract: Identifying key evolutionary strategies that support population persistence remains a challenging task for biodiversity conservation. Here we assess if animal adaptations to cope with low densities (i.e. that facilitate mate-findings or promote spatial aggregation of individuals) can allow species to persist in human-altered habitats.
A spatially explicit and individual-based model was developed to assess if, and under what circumstances, such adaptations maintain population viability. The model was parameterised with data from the movement and demography of the spur-thighed tortoise (Testudo graeca) and simulated scenarios with differences in adult survivorships, initial population sizes and habitat alterations. Habitat alterations reduced population viability, and extinction rates were dependent on population characteristics and mate-finding distance. In contrast, philopatry around the birthplace did not prevent extinctions. Our results highlight the importance of considering specific spatial traits of species when assessing their vulnerability to human habitat alterations.