Experimental Habitat Fragmentation Reveals a Shift in the Isotopic Niche of the Forest Wood Scorpion, Cercophonius squama

Perryman, Nolan

Undergraduate Honors Thesis

Experimental Habitat Fragmentation Reveals a Shift in the Isotopic Niche of the Forest Wood Scorpion, Cercophonius squama Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/pn89d763v

Abstract

Habitat loss and fragmentation are widely referred to as leading causes of altered community interactions and loss in biodiversity. The present research examined fragmentation-induced changes to the dietary niche and distribution of a generalist species, which is able to shift between prey items and can be resistant to fragmentation. We tracked the distribution of the forest wood scorpion, Cercophonius squama, over the course of seven years across an experimentally fragmented landscape to determine its response in abundance to habitat fragmentation. Next, we considered how cascading effects, resulting from the loss of species can result in the trophic downgrading of ecosystems. The ¹⁵N /¹⁴N and ¹³C /¹²C isotope ratios present in the tissue of C. squama represent protein components of their prey items and were used as a reflection of potential changes in the trophic structure of an experimentally fragmented food web. Given the habitat fragmentation treatment, we predicted that the isotopic niche of an abundant generalist predator would reflect trophic downgrading, which results from the loss of higher-trophic species in an ecosystem. Accordingly, we predicted that C. squama would feed, on average, at a lower trophic level in fragments and their surrounding matrix, than adjacent, undisturbed and continuous forest. Our results were, however, in contrast to our prediction; namely, d¹⁵N values were on average highest in the fragments. We show that current theoretical models that predict trophic downgrading of ecosystems might not adequately translate to the invertebrate food web. Further, our research examined the isotopic niche of C. squama and determined that abiotic and biotic factors resulted in changes to the niche of the scorpion in fragments and the matrix compared to controls. Our findings increase our understanding of how habitat fragmentation and the introduction of a non-native Monterey pine matrix shapes the niche of a generalist predator and alters the invertebrate food web.

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