NKNMMA004
Abstract
Introduction
Spiders are obligate predators that thrive in a wide range of terrestrial environments
(Nentwig,1983).Wilgers(2016) suggests they prey on a wide range of living organisms
including insects ,other spiders and small vertebrates. Spiders are among the prepotent
predators on earth (Wise 1993; Bond et al. 2014; Cushing 2017).They are of the order
Arachnida (Pressman and Dufresne,2013). There are about 113 families in this order.
In this study , two families were identified ,Pisauridae (nursery web or fishing spiders) and
Araneidae (Orb-weaver spiders).Hammond (no date) stated that Orb-weavers live anywhere
there are prey and structures that can buttress their webs. They are much more common in
humid habitats than in dry ones(Hammond,no date).These areas can include areas around
night-lights, tree branches, tall grass, weeds, fences, walls and bushes.They use spinnerets
to form silk with which they use to form webs to catch prey (Pressman and
Dufresne,2013).
Similar to Orb-weaver spiders, nursery web spiders inhabit areas where there is tall grass
and shrubs.Pisauridae webs are not built to capture prey .This family of spiders have have a
great sense of movement for that reason, they rely on that ability to capture their prey .
Instead of comparing and contrasting insects and spiders quantities,we will be referring to
spiderwebs and not actual spiders due to the fact that they actually represent the spiders we
couldn’t possibly see occupying that particular web. Spiders hide away from predators while
keeping their eye on their web in case any prey falls into their trap.
According to Nentwig (1983) ,analyses of their prey spectrum of spiders have been rare in
reports.
Problem
Is there any correlation between the number of spiderwebs and insects at Grootbos Nature
Reserve.
Does vegetation height affect the number of spiderwebs or insects ?
Hypothesis
We came up with two hypotheses . The first one was that areas with a great abundance of
spiderwebs will have a plethora of insects due to spiders preferring a location that has
sufficient prey for their consumption .Second to the first hypothesis is that, in areas where
there are plenty spiderwebs present , the insect quantity should be low as a result of many
spiders being present ,leading to a fewer insects present after they have been devoured by
these predators.
This study was conducted to investigate if there is a predator-prey relationship between
spiders and insects.The definition of a predator prey relationship is the interactions between
a species (predator) that eats another species(prey) (Pressman and Dufresne,2013).
Methods and Materials
A red and white tape was used to demarcate the location for data collection.We planted two
sticks and used the tape of this 18m to indicate to people walking by to not cross to the other
side of the tape so they don't interrupt the traps we are to set. We divided the demarcated
area into two transect lines and named them transect line 1 and transect line 2.We used a
measuring tape to measure a distance of 15m in transect line1 and 17m in transect line 2
.We dug 5 holes with a wooden stick which were 3m apart.Next to each whole we planted a
stick and tied a piece of tape to easily spot the hole.
The same procedure was followed in transect line 2 with an extra hole making them 6 holes
in total for transect line 2. We used clean plastic cylindrical containers with a diameter of (to
be confirmed) to set pitfall traps.Inside each container was 5 pumps of ethanol which was
stored in a wash bottle. We cut approximately 3 cm of masking tape with our hands and
stuck it on each pitfall container. We then used a permanent marker to label transect line 1
containers 1A-1E and labelled transect line 2 containers 2A-2E and 2AA with whom we
started planting from the tape and the rest following to the last hole of the transect line.At
17:45 in the afternoon, we started to alphabetically plant the open containers into the holes
we dug , starting from where our demarcating tape was placed to the end of the row .When
planting the pitfalls traps we made sure to avoid soil accidentally falling into our traps .
The next day at 09:00 we started measuring quadrats with 2m dimensions using a
measuring tape, where one side was along the line of the planted pitfall trap and with the
pitfall trap being right in the middle of that one side.Within each quadrat we counted the
number of spider webs visible and spiders if spotted any.We used a 30cm ruler to measure
the height of the vegetation within that quadrat where selection was random.About 3
measurements were recorded with a pen into a book and the average height was
determined using a casio calculator and was recorded too.In each quadrat different types of
plants were identified ,if unknown ,it was plagued out then put into a ziploc bag to be
identified later with assistance.This procedure was repeated for all the 11 quadrats.
Later on at 11:00 , we started to remove the pitfall traps and sealed the containers for insect
identification in the working area.Plants experts helped us identify the plants and data was
recorded in a spreadsheet created using excel.We started to identify the insects we were
able to collect.For each pitfall trap container ,we emptied the contents into a petri dish and
and identified the insects that we were big enough to be seen and used a spatula suck the
insects out of the petri dish into the glass vials or used tweezers to pick the insects and
transfer them into the same glass vial while making sure the unified insects remain in the
petri dish.We pumped ethanol with into the glass vials ,until it was mid way the glass
vial.Using a masking tape and permanent marker we labelled the glass vial in
correspondence with the pitfall trap container labelling .In case the labelling came off we cut
a small piece of paper labelled it too and threw it inside the glass vial. For the insects that
were too small to be seen with human eye ,we placed the petri dish under a compound
microscope.Moving the petri dish around to make sure none of them were left out.Having
done that procedure we used the same method to transfer the insects into the glass
vials.This procedure was repeated for all the pitfall traps containers.Not all insects were
identified on that day .All the glass vials had to be carefully cushioned with paper towel in a
yoghurt container so to be identified at the biology labs on UCT upper campus.To identify the
remaining insects we used the same procedure with the help of insects experts whom were
not available at our disposal during the field trip and some pictures were taken and uploaded
into Naturalist to get feedback other experts from different walks of life.
The data was uploaded into Excel which was also used to create regression analyses of the
data and for generating t test output.
Results and data analyses
Correlation .
Fig.2 A depiction of the correlation between spider webs and the number of insects.
Fig.2 A depiction of the correlation between vegetation height and the number of insects.
Fig.3 A depiction of the correlation between vegetation and spider webs count.
T Test analyses.
Discussion
Conclusion
Reference