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Effects of Climatic Variation on Small Mammal Population

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Researchers have long focused on how the biotic factors, rather than abiotic factors, impact small mammal population dynamics. This study focuses on how the abiotic factors (e.g., climatic variation) impact small mammal population densities in southeastern Ontario. I analyzed a long-term (1964-2013) live-trapping dataset from the Falls macrohabitat in Algonquin Provincial Park. From the dataset, I determined the small mammal population densities per year (total captures/trap night) and asked whether these densities are correlated with earlier ice-out dates. The long-term trend did show an increase in small mammal population densities with earlier ice-out dates, however, the relationship was not significant (p > 0.1). Changes in small mammal densities due to climate change could affect their interactions with terrestrial ecosystems and result in a reduction in biodiversity.

Introduction

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How biotic and abiotic factors influence population size continues to be a topic of debate for many ecologists. Many studies focus on the importance of biotic factors as a cause for population fluctuations, however, few studies focus on the importance of abiotic factors (Dhawan et al. 2018). Abiotic factors (e.g., temperature) fluctuate year-to-year but with climate change, there can be longer term changes (e.g., decadal oscillations). Understanding how these long-term changes in climate will affect different species/taxa is crucial for biodiversity and conservation management.

Temperature is a key abiotic factor influencing ecological processes and plays a pivotal role in the Metabolic Theory of Ecology (MTE) (Reuman et al. 2014). MTE predicts a general increase in metabolism with increasing temperature and decreasing body size. Increasing temperatures due to global warming have the potential to increase the metabolic rate in organisms, such as small mammals.

Small mammals play vital ecological roles in terrestrial systems (large biomass, consume plants and invertebrates, prey of several predators, and vectors and hosts of disease), making them useful bioindicators of climatic variation over time. Additionally, small mammals are ideal model species for examining the effects of climatic variation as they have short lifespans and fast life-history strategies that allow them to adapt to changing environments.

The purpose of this study was to examine the impact of climatic variation on small mammal population densities in Algonquin Provincial Park. I hypothesized that earlier ice-out dates caused by global warming results in increased metabolism in small mammals, due to the Metabolic Theory of Ecology. Therefore, if earlier ice-out dates lead to increased metabolism in small mammals, then earlier ice-out dates will result in an increase in small mammal population densities.

Methods

This study used pre-collected data between 1964 and 2013 from Algonquin Provincial Park. Algonquin Provincial Park is in southeastern Ontario and is composed of forests, rivers, and lakes. Data between 1964 and 2008 were used from Brooks 2008 report to the OMNR. Data were collected from 2009-2013 by Dr. Andrew McAdam of the University of Guelph. The data collected focused on 9 small mammal species including: deer mouse (Peromyscus maniculatus or Peromyscus leucopus), red-backed vole (Myodes gapperi), chipmunk (Tamias striatus), woodland jumping mouse (Napaeozapus insignis), meadow jumping mouse (Zapus hudsonius), short-tailed shrew (Blarina brevicauda), soricid shrews (Sorex spp.), northern flying squirrel (Glaucomys sabrinus), and North American red squirrel (Tamiasciurus hudsonicus). The data consisted of two macrohabitats within Algonquin Provincial Park: Falls and Conifer.

This study focused on data from the Falls. The Falls data was reduced to Year, Ice-out date, Trap nights, and Total small mammal captures. Total small mammal captures were divided by trap nights to yield small mammal density (total captures/trap night). A simple linear regression was performed on year and ice-out date to see if there is a relationship between year and earlier ice-out dates. Ice-out date was log transformed to linearize the relationship. A simple linear regression was performed on ice-out date and small mammal density to see if there is a relationship between earlier ice-out dates and small mammal density.

The findings of my study show that there is a long-term trend of earlier ice-out dates over time. However, there does not appear to be a significant relationship between earlier ice-out dates and small mammal population densities. These results do not support my hypothesis that earlier ice-out dates caused by global warming will result in increased metabolism in small mammals, due to the Metabolic Theory of Ecology.

Since I looked at total small mammal captures per year, it’s possible that population densities of some species increased while others decreased. This could have resulted in no overall change in small mammal density. Myersexamined the impact of climate change on small mammal communities of the Northern Great Lake Region. They found that southern species (white-footed mice, eastern chipmunks, southern flying squirrels, common opossums) showed increased abundance and northern species (woodland deer mice, southern red-backed voles, woodland jumping mice, least chipmunks, northern flying squirrels) showed decreased abundance. Therefore, analyzing the species individually and looking at total species captures per year could provide more insight into the effects of climate change on a species level.

 Previous studies have shown that long-term warming trends can reduce cyclic fluctuations in small mammal populations (Dhawan et al. 2018). The study conducted by Ecke et al. (2017) suggests that a reduction of population cycles in small mammals can result in a change in structure of small mammal communities, a decrease in diversity and an increase in the transmission of zoonotic diseases.

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