EPOW - Ecology Picture of the Week

Ecosystem Engineer With a Shell

Galapagos Giant Tortoise (Geochelone elephantopus vandenburghi), Family Testudinidae
Isabela Island, Galapagos Islands, Ecuador

Explanation:  Here's a hearty survivor we've met before.  But this time we are viewing its amazing feats of ecosystem engineering.  

An ecosystem engineer is an organism that can create structures or that can change its environment in some significant way that can be used by, or that otherwise influences, other species.  

Here we have a Galapagos giant tortoise.  We indeed are in the Galapagos Islands of Ecuador, more specifically, Isabela Island ... and more specifically, Urbina Bay on Isabela Island.  

Here, the tortoises descend from the slopes of Alcedo Volcano during the rainy season in response to vegetation dynamics (Blake et al. 2013).  Then, through browsing and trampling, the tortoises maintain large openings, such as the one shown here, dominated by the native hairy ground cherry (Physalis pubescens).  

These ecosystem engineering feats significantly alter the habitat for other species, in particular for some songbirds and finches that use the openings for feeding or nesting.

It is an amazing relationship between reptile, vegetation, and volcano.  

Information:
     Blake, S., C. B. Yackulic, F. Cabrera, W. Tapia, J. P. Gibbs, F. Kümmeth, and M. Wikelski. 2013. Vegetation dynamics drive segregation by body size in Galapagos tortoises migrating across altitudinal gradients. Journal of Animal Ecology 82(2):310-321.