Concurrent climate induced range contraction in herbivore and primary producer

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Mary R. Cortese, Department of Biology, Temple Univeristy, Philadelphia, PA and Amy L. Freestone, Department of Biology, Temple University, Philadelphia, PA

Background/Question/Methods
As global oceans get warmer, species are moving poleward to reduce thermal stress. As species ranges change, so do their interaction networks leading to trophic mismatches and creating the potential for concurrent movement of dependent species. In ocean systems these range movement are occurring at faster rates than in terrestrial systems, highlighting the importance of quickly establishing accurate predictions of range shifts, especially for organisms with high ecological and economic importance. This study aims to understand how species interactions alter range movements to better predict community dynamics under global change. We address these complex dynamics in the Eastern Pacific kelp forest ecosystem by modeling herbivory interactions in a Species Distribution Modeling framework. Giant kelp (Macrocystis pyrifera) forms the foundation of the forest, with purple sea urchins (Strongylocentrotus purpuratus) as the dominant herbivore with strong preference for M. pyrifera. Using Maxent, we first modeled the distribution of giant kelp under current day and climate change scenarios. We then modeled the purple urchin’s current day and climate change distribution using only environmental variables and then a second time with kelp presence included as a predictor variable.
Results/Conclusions
Preliminary model results demonstrated concurrent range contraction in the southern edge of both species ranges. This pattern was not apparent in models of the purple urchin without giant kelp, indicating the importance of integrating species interactions into modeling frameworks, particularly when planning for global change. Jackknife analysis showed a high variable importance for kelp and temperature as predictor variables in purple urchin models (number 1 and number 2 in percent contribution respectively), further demonstrating the importance of primary producer availability for herbivore species distribution. While less studied than northern range expansions, concurrent range contractions at the southern range edge in this system may have important ecological consequences for the broader network of associated species and their economic viability.