SC5202 Cattle Stocking Regime and Body Size in Bynoe’s Gecko Assignment Sample

Contents

Abstract

Introduction

Methods

Results

Discussion and Conclusions

References

Abstract

Problem statement: Wambiana cattle station near Charters Towers, 150 km to the west of Townsville, is run as a large experiment using five different cattle stocking regimes. We have been given access to a subset of the survey data, and are focussing only on the morphology data from Bynoe’s gecko (Heteronotia bynoei).

Motivation: The owners, managers, and researchers are interested in the effect of these stocking treatments on the amount of profit they make (via beef cattle sales), but also whether each stocking regime is beneficial or detrimental to the wildlife and native habitat also within these paddocks.

Approach: Each year, JCU Wildlife Ecology & Management (BZ3740/BZ5740) students carry out vertebrate surveys within the paddocks of two of these treatments: ‘high stocking rate’ (HSR) and ‘moderate stocking rate’ (MSR).

1. Within each year, sampling effort is equal on the high and moderate treatment paddocks. There are also two different woodland habitats, Box Gum and Ironbark woodland.

2. There is more Box Gum habitat than Ironbark habitat, but each treatment paddock has equivalent areas of each habitat type.

Boxplots to measure difference between groups, Hypothesis testing to determine whether any of the differences were significant, what are the implications of the hypothesis test and what are the caveats from our findings. We assume the conditions for inference to be generally true as the sample size is greater than 30 and the sample proportions are uniform.

Results:

1. No significant difference in SVL for groups with moderate and high stocking rates.

2. Mean SVL for group with moderate stocking rate is 38mm.

Introduction of Cattle Stocking Regime and Body Size in Bynoe’s Gecko

The two questions we need to answer are:

1. Is the body length of Bynoe’s gecko (as measured by snout-vent length, SVL) different between ‘high’ vs. ‘moderate’ levels of cattle stocking?

2. Does the mean body length (SVL) of Bynoe’s gecko found in the ‘moderate’ grazing habitat differ from 42.625 mm, which is the mean body length in unstocked woodlands*?

*Zozaya et al. (2019) found that the average body length of Bynoe’s geckos in unstocked woodland in the same region was 42.625 mm. This average taken from ‘EA6’ genetic lineage SVL measurements in the Supplementary Material of Zozaya et al. (2019).

Methods of Cattle Stocking Regime and Body Size in Bynoe’s Gecko

Each year, JCU Wildlife Ecology & Management (BZ3740/BZ5740) students carry out vertebrate surveys within the paddocks of two of these treatments: ‘high stocking rate’ (HSR) and ‘moderate stocking rate’ (MSR).

At each of these sites, the JCU students use three different survey techniques to count and measure vertebrate animals:

1. Active Search (opportunistically searching during the day by looking carefully through the habitat),

2. Pit & Funnel Trapping (fixed traps dug or secured into the ground), and

3. Spotlighting (opportunistically searching at night with a head torch).

Animals are carefully handled and various morphology measurements are taken, as well as whether the animals are juvenile or adult female or male.

Results of Cattle Stocking Regime and Body Size in Bynoe’s Gecko

Snout-vent length has a minimum of 13.5mm and a maximum of 75mm,with a mean of 37mm.

We observe there is a slight difference between body lengths of those geckos with moderate and high stocking rate.We perform hypothesis tests to see if the difference is in any way, statistically significant.

A one-sided hypothesis test is performed using the inference function from the statsr package,which produces helpful outputs along with performing hypothesis tests, which is valuable for our analysis. with the mean snout-vent length being less for those with high stocking rate. Results show a p-value of 0.2615(>0.05). Thus there is no significant difference of body-length between groups with high and moderate stocking rates. Below are the sample distributions and density associated with the hypothesis tests

The other question, mean body length in areas with moderate stocking rates is 38mm,and not close to the 42.625mm listed in the original text. 

Discussion and Conclusions of Cattle Stocking Regime and Body Size in Bynoe’s Gecko

1. There is no statistically significant difference between those geckos in areas with high or moderate stocking rates.

2. Mean body length is 38mm in areas with moderate stocking rates and not the 42.625mm listed in the text

It is to be noted that we had access only to 73 samples from the full dataset, which was specifically curated for analysis. High variance might have skewed results one way or the other. With a small sample size, it is difficult to measure the real effect of stocking rates, as we do not know what kind of sampling was done from the dataset. Nevertheless, we have assumed the conditions to be true for the purpose of this analysis.

There is more potential for analysis on basis of habitats and sex of the geckos, which could be deciding factors. Do male geckos get larger than female geckos? Is the presence of more animals in the Box Gum habitat a skewing factor?

More detailed questions need to be asked to get the full picture.

References

“Wambiana Grazing Trial.” FutureBeef, 22 Mar. 2017, futurebeef.com.au/projects/wambiana-grazing-trial/.

Clyde, Merlisse, et al. “ [R Package Statsr Version 0.2.0].” The Comprehensive R Archive Network, Comprehensive R Archive Network (CRAN), cran.r-project.org/web/packages/statsr/index.html.

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