The Hawaiian term "kipuka" refers to a variation or a change in form.  Forest kipukas are formed when a continuous forested habitat on the slope of an active volcano is covered by a fresh lava flow.  Small remnant islands of forest are left behind in a sea of new lava.

Over time, plants and animals remaining in these patches and from surrounding areas recolonize the new lava flow, generating a mosaic of successional habitats.  This is a continuous process spanning the life of the volcano.

I have been investigating the ecological and genetic impacts of habitat fragmentation in a  system of forest kipukas located on the northeastern slopes of Mauna Loa volcano on the Big Island of Hawaii.  This system offers a unique opportunity to study the effects of natural fragmentation on a native ecosystem over known periods of time.

The abiotic and biotic conditions inside forest kipukas differ tremendously from those on the surrounding lava flows. Native Hawaiian Tetragnatha spiders respond to this difference as well, with  a dramatic change in species composition in the two habitat types.

Populations of spiders that are limited to the interior forest habitat in different kipukas may be isolated from one another, despite the relatively short geographic distances between these patches.  This isolation can then lead to genetic divergence among populations.  Each isolated population may be on its own evolutionary trajectory. Alternatively, the dispersal capabilities of organisms between kipukas may be maintaining populations in fragments, as well as maintaining gene flow between these populations.



I  investigated population genetic differentiation in three species of spiders in isolated kipukas (Tetragnatha quasimodo, Tetragnatha brevignatha and Tetragnatha anuenue.) using a combination of allozyme and mtDNA markers.  Results suggest that T. anuenue and T. brevignatha show some population genetic differentiation among isolated populations found in different forest kipukas, but that T. quasimodo does not.   These results reflect these species ecological roles.  Both T. anuenue and T. brevignatha are restricted to forest kipukas.  In contrast T. quasimodo is a habitat generalist, and is found on surrounding lava flows as well as in the forest fragments.






This research was conducted in collaboration with George Roderick (Ph.D. advisor) and Rosemary Gillespie (Co-advisor).  Currently we are investigating the link between the formation of volcanoes on the Big Island of Hawaii and patterns of gene flow and genetic differentiation among populations within these species.  

T. brevignatha
photo by R. Gillespie