Document Type

Honors Thesis

Publication Date

Spring 5-2017

Abstract

Northern water snakes (Nerodia sipedon sipedon) have a disjunct geographic range in the northeastern part of their distribution, specifically in Maine with one occupied region about 125 kilometers from any other known population. This gap could be due to a number of factors with some currently affecting the species including dispersal and habitat characteristics, while some factors may have historically affected their distribution, such as retreating glaciers and climate change. We assessed the effects of lake characteristics and bioclimatic variables on the range of N. s. sipedon within Maine using a logistic regression built from a generalized liner model. Lake characteristics (e.g. pH, surface temperature, and area) did not affect snake presence within their range, but bioclimatic variables did show statistical significance. In particular, lakes where the snakes were present were warmer than lakes where they were absent. When the bioclimate of the eastern range of N. s. sipedon was compared to the range gap the best model based on AIC scores showed that mean temperature of the warmest quarter, annual precipitation, and annual mean temperature were different between the areas. Bioclimatic variables also explained the restriction on N. s. sipedon expanding their range northwards. We conclude that bioclimatic variables have a large effect on the current distribution of N. s. sipedon within Maine and can help explain why the range gap persists.

Download

Share