Joseph Rubio
Erica Atkins
BSC 2011L
12, April 2021
African Bush Elephant (Loxodonta africana) Abundance During Wet and Dry Season
Abstract
The abundance of a species is the amount of individuals present in a specific habitat or
environment. Species abundance can be affected by a variety of environmental variables. Since
the species Loxodonta africana are mostly found in Africa and whose feeding habits change with
the seasons, a study was conducted in order to find if the environmental variable, dry and wet
seasons, affect the abundance of L. africana in Mozambique. In order to observe the amount of
african elephants present in Mozambique, pictures of the elephants were captured via WildCams
in trails and were separated into two categories: dry season and wet season. The averages of african
elephants captured in each season proved that there were slightly more elephants present during
the dry season than the wet season. These results show that environmental variables can have an
affect on the abundance of a species in their habitat. Other studies conducted on other mammals
and fish in Africa have also provided evidence that environmental variables such as the change in
season can influence the abundance of a species.
Introduction
The study of the relationships between different organisms and their environment is ecology. One
of the topics of ecology is species abundance, which refers to the amount of individuals in a species
compared to another species in a set environment. Knowing the abundance of a species in a given
location can give us an understanding of how that community of organisms functions and interacts
with the environment, and can also give us insight on how these interactions can change
abundances of a species. Several authors have studied the many possibilities that can cause a
change in the abundance of a species (Lingzhao, T. and Peng Z. 2020; Shimadzu, H. et al. 2013).
These mensurative experiments gave similar results even though they were all tested on different
species, there is a possibility that an environmental variable could change the abundance of a
species.
The different seasons of an environment is a key variable that can lead to changes in species
abundance. The specific season of a defined environment could cause the abundance of a species
to increase or decline depending on the species being studied. Shimadzu (2013) proved how
seasons can affect the abundance of a species by studying fish for 30 years and found that different
species of fish separate themselves into different seasonal groups to lower the competition for
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food. This experiment showed how the difference in the seasons affected the abundance of a
species by different species appearing at specific seasons to feed.
The difference in seasons in Mozambique is a great variable to study the abundance of all
the different species living in that environment. One species that lives in this environment and
whose abundance is affected by the different seasons is the African Bush Elephant, Loxodonta
africana. African elephants are found in a plethora of habitats with different seasons such as the
savannah and rainforest. The African bush elephant is perfect for the study of environmental
variables affecting species abundance because their feeding depends on the season they are
currently in since they are particular about their diet. I believe the abundance of the African Bush
Elephant is greater in the dry season. Specifically, I asked if the season of the environment affects
the abundance of elephants.
Methods
In order to determine if the change in seasons affects the species abundance of african elephants,
a sample of L. africana must be observed over time. The L. africana are mostly located across
Africa and are found in different habitats around the continent. They are commonly found in the
savannah and mostly inhabit areas with a high abundance of water and vegetation. African bush
elephants mostly graze and the seasons usually affect how they eat. They are more picky eaters
during the wet season than the dry season.
A collection of Wildcam images of the L. africana were selected from the WildCam
Gorongosa Lab that has trail cameras set up across Mozambique. The Wildcam took pictures of
several different species in different locations across Mozambique. We specifically searched for
images of the african elephant. Once we found where the images of the elephants were captured,
we focused on the areas where most of the images of elephants were captured to ensure that the
environmental variable of the seasons would make a significant difference in the abundance of
elephants.
We explicitly focused on Wildcam images of african elephants taken during the night
because this is when they were most active. Since we knew that the seasons can have an effect on
where the L. africana decide to feed, we focused on the dry season and wet season as the
environmental variable and made these our treatment groups. We then compared the abundance of
african elephant abundance at night during the dry season and wet season. Due to the fact the same
image of the same elephant might have been captured more than once we used three cameras for
both seasons and evaluated the averages of appearances captured to acknowledge the same
elephant picture being captured more than once.
Results
Both treatment groups, being the wet and dry seasons, showed an abundance of L. africana in the
area during night. In the dry season treatment group, a total of 820 photos of african elephants
were taken (mean (M)=1.47, standard deviation (SD)=0.46) and 33 photos were captured of african
elephants during the wet season (M=1.22, SD=0.38). However, our averages showed that there
were slightly more african elephants in abundance during the dry season than the wet season
(T=0.72, df=4, P=0.51 Fig. 1). Since we failed to reject the null hypothesis, the season of
abundance does not seem to influence the abundance of the L. afriana.
Figure
2
Fig. 1. The amount of L. africana that were observed in Mozambique at night during both the wet
and dry seasons. 820 photos of african elephants were captured during the dry season and 33 photos were
captured during the wet season. The average number of african elephants accounts for the photos containing
the same elephant more than once. Graph 1: Depicts the average number of elephants observed during the
dry season. Graph 2: Depicts the average number of elephants observed during the wet season. There were
slightly more elephants observed in the dry season than the wet season (P>0.05 t-test).
Discussion
L. africana were more in abundance during the dry season than they were in the wet season.
These results support the hypothesis that the abundance of african bush elephants are higher during
the dry season. The prediction that the african elephants would prefer the dry season more than the
wet season was plausible following the research done by Kiffner (2014) in which mammal species,
including african elephants, found in East Africa were observed to see if seasons affect species
abundance of different species; in which the results showed that different species were more
abundant during the dry season possibly due to limited resources. This prediction on the african
elephants being more abundant during the dry season was also logical due to the fact that the L.
africana prefer to feed during the dry season because they are less picky about what food they
consume. The similarity of the results from the study conducted by Kiffner in 2014 and this study
conducted on african bush elephants provide sufficient evidence that elephants are higher in
abundance during the dry season.
The study conducted proved that a species abundance can be affected by an environmental
variable, such as a difference in seasons. Previous studies conducted on ecology show a variety of
environmental variables affecting the abundance of a species. Using fish as the dependent variable,
Shimadzu (2013), noticed that the variation in species abundance seemed to coincide with the
seasons. The study followed a large assemblage of fish for over 30 years which showed difference
in species abundance depending on the season they were in, mostly due to the fact that each
different species of fish were reducing competition for food against one another to keep the
population of each species intact (Shimadzu et al. 2013). The fact this study was conducted on an
entirely different species and an environmental variable was still the case for the change in species
abundance as it was in the study conducted on L. africana prove that environmental variables are
one of the main causes for species abundance in any habitat.
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Due to our results failing to reject the null hypothesis, we know that seasons don't affect
the abundance of elephants present. The next logical experiment to further the results of this study
would be to test another environmental variable that could affect the abundance of african bush
elephants. Comparing the elephants to the test done on fish by Shimadzu (2013) the other variable
that may need to be studied are the abundance of other species that may affect the abundance of
african elephants. Additionally, could competing herds of L. africana be the variable that affects
the abundance of elephants in a given area?
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