Habitat and population structure of the Morelet’s crocodile (Crocodylus moreletii) in Calakmul Biosphere Reserve, Campeche, Mexico

Barão-Nóbrega, JAL

Abstract

The Yucatan Peninsula (YP) is one of the most recognizable parts of Mexico and is well known as one of the significant areas in Mesoamerica which supported the Mayan civilization. In the southern portion of the Peninsula, natural aquatic habitats occur at relatively low densities across the region in the form of semi-temporary ponds (aguadas) sustained by rainfall, and constitute the only local source of standing water during most of the year to both the fauna and human communities. The Morelet’s crocodile (Crocodylus moreletii) is an apex predator and a flagship species inhabiting these aquatic environments, but only rudimentary information about this species exists in the region.

This PhD project contributes to current knowledge on aquatic habitat in Calakmul Biosphere Reserve (CBR) and characterizes aguada habitats across the region through information on their general structure and water quality. Such inferences provide a baseline to investigate the population structure of C. moreletii within and around CBR through N-mixture modelling to estimate local abundances and population sizes, and population genetic analyses using SNPs generated through a double-digest RADseq approach (dd-RADseq).

A total of 85 waterbodies were located and described throughout CBR, out of which 64 were annually monitored for water level and vegetation cover from 2016 to 2019, providing detailed data on shape and size variation in response to fluctuations in annual precipitation. A citizen science project was also designed for long-term monitoring of aguadas using standardised data entry forms and information uploaded through a mobile app to a centralized online database. N-mixture models applied to count data (n = 1,105 crocodiles) from 256 spotlight surveys conducted across 50 representative aguada locations have resulted in estimates of crocodylian detection and abundance, with covariates enabling insights into population responses to local environmental conditions. Extrapolating abundance estimates across Calakmul yielded in ~12,000 C. moreletii present, demonstrating that the region is an important global stronghold for this species. Population structure assessment of C. moreletii showed that CBR still harbours genetically pure individuals, whereas genetic pollution through increased hybridization with the American crocodile (Crocodylus acutus) is common across other parts of its range. This assessment also revealed that the six main geographical regions within Calakmul where samples originated from to a large extent represent own genetic clusters, and spatial population structure is highly linked to extended family networks within each region.

Taken together, the findings of this PhD will play an essential role in management actions towards the conservation of C. moreletii populations in aguadas, establishing C. moreletii as an umbrella species for the biodiversity that occurs in them.

Citation

Barão-Nóbrega, J. Habitat and population structure of the Morelet’s crocodile (Crocodylus moreletii) in Calakmul Biosphere Reserve, Campeche, Mexico. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Apr 21, 2021
• Publicly Available Date: Apr 21, 2021
• Additional Information: Funders : Operation Wallacea & University of Salford (ICase PhD studentship);IUCN/SSC Crocodile Specialist Group;NERC’s Biomolecular Analysis Facility
• Award Date: Jan 1, 2021