Geology topics

Freddy Cabrera

Publications and source records attributed to Freddy Cabrera.

3 recordsLinked to original sources

USGS2021

Movement ecology

(Yackulic) At first glance, the decision to study movement in Galapagos tortoises seems curious. Given the slow speed of tortoises and tendency to forage and rest as they move, it seems implausible that tortoises would string their slow bursts of activity together to accomplish large-scale movements. Nonetheless, as early as 1815 (Porter 1815), visitors to Galapagos have noted the propensity for tortoises to walk long distances along well used trails, leading to seasonal changes in the distribution of tortoises on the various islands of the Archipelago. In recent years, advances in the technology used to track animals have led to a better understanding of movement and the diversity of movement strategies among many animal taxa. This chapter focuses on the application of these technologies to study of movement in Galapagos tortoises. Recent work has shown not only the diversity of movement strategies employed by Galapagos tortoises, but also illustrated how movement can both cause and be a consequence of interaction between reproductive and foraging ecologies of tortoises and the presence of strong environmental gradients. Understanding how critical unimpeded movement is to the persistence of Galapagos tortoises also informs efforts to maintain connectivity to, and suitable habitat within, tortoise range outside of protected areas.

Book chapter↗

USGS2019

Migration triggers in a large herbivore: Galapagos giant tortoises navigating resources gradients on volcanoes

To understand how migratory behavior evolved and to predict the future of migratory species in the face of global environmental change it is important to quantify intra- and inter-individual variation in migratory behavior. Intra-individual variation includes behavioral response to changing environmental conditions and hence behavioral plasticity in the context of novel conditions. Inter-individual variation determines the degree of variation on which selection can act and the rate of evolutionary response to changes in average and extreme environmental conditions. Here we focus on variation in the partial migratory behavior of Galapagos giant tortoises ( Chelonoidis spp.), which exhibit high fidelity to migratory routes over many years. We evaluate the extent and mechanisms by which tortoises adjust migration timing in response to varying annual environmental conditions, integrating movement data within a bioenergetic model of tortoise migration to quantify the fitness consequences of migration timing. We find strong inter-individual variation in the timing of migration, which was not affected by environmental conditions prevailing at the time of migration but rather by marginal expectations estimated from multi-annual averaged conditions, leading to an average annual loss in efficiency of ~15% relative to optimal timing based on year-specific conditions. These results point towards a limited ability of tortoises to adjust the timing of their migrations based on prevailing (and, by extension, future) conditions, suggesting that the adaptability of tortoise migratory behavior to changing conditions is predicated more on past “normal” conditions than responsive to current, changing conditions. Our work offers insights into the level of environmental-tuning in migratory behavior and a general framework for future research across taxa.

Galapagos Islands↗

USGS2016

Allometric and temporal scaling of movement characteristics in Galapagos tortoises

Understanding how individual movement scales with body size is of fundamental importance in predicting ecological relationships for diverse species. One-dimensional movement metrics scale consistently with body size yet vary over different temporal scales. Knowing how temporal scale influences the relationship between animal body size and movement would better inform hypotheses about the efficiency of foraging behaviour, the ontogeny of energy budgets, and numerous life-history trade-offs. We investigated how the temporal scaling of allometric patterns in movement varies over the course of a year, specifically during periods of motivated (directional and fast movement) and unmotivated (stationary and tortuous movement) behaviour. We focused on a recently diverged group of species that displays wide variation in movement behaviour – giant Galapagos tortoises ( Chelonoidis spp.) – to test how movement metrics estimated on a monthly basis scaled with body size. We used state-space modelling to estimate seven different movement metrics of Galapagos tortoises. We used log-log regression of the power law to evaluate allometric scaling for these movement metrics and contrasted relationships by species and sex. Allometric scaling of movement was more apparent during motivated periods of movement. During this period, allometry was revealed at multiple temporal intervals (hourly, daily and monthly), with values observed at daily and monthly intervals corresponding most closely to the expected one-fourth scaling coefficient, albeit with wide credible intervals. We further detected differences in the magnitude of scaling among taxa uncoupled from observed differences in the temporal structuring of their movement rates. Our results indicate that the definition of temporal scales is fundamental to the detection of allometry of movement and should be given more attention in movement studies. Our approach not only provides new conceptual insights into temporal attributes in one-dimensional scaling of movement, but also generates valuable insights into the movement ecology of iconic yet poorly understood Galapagos giant tortoises.

Journal of Animal Ecology↗