Epiphyte relationships between organisms are maintained (Feld et al.

Epiphyte Diversity
in Response to Human Presence

 

 

 

 

Abstract

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

 

            How
humans change diversity is an interesting question in the field of ecology.

This study aims to gain insight into how human disturbances can affect the
diversity of organisms, specifically epiphytes, by seeing if human urbanization
causes a change in epiphyte diversity compared to a natural and more
undisturbed environment. We hypothesized that epiphyte diversity would be
different in the urban and natural environments because of the effects of human
disturbance. To test this we chose two sites, Main Mall on the UBC campus as
our urban site and Pacific Spirit Regional Park as our natural site. We then
used transects and quadrats to find the diversity values of epiphytes on trees
in each of these two sites. We also used dissimilarity values to further look
for differences between the two sites in epiphyte composition. We found that
there were greater differences in epiphyte composition between the urban and
natural site than within these sites and that the epiphyte diversity values
were significantly higher in the urban site. These results were unexpected, but
they point to the idea that multiple factors are at play when considering
epiphyte diversity and composition in urban environments.

 

 

 

 

Introduction

 

            Biodiversity
is an important aspect of the environment as more diverse habitats are able to
function better as important mechanisms are maintained (Feld et al. 2010). Having more species
ensures that important ecosystem services are being met and that relationships
between organisms are maintained (Feld et
al. 2010). Humans, though, are threatening this biodiversity as urban
spread is increasing throughout the world and this makes the potential habitats
for other organisms smaller and smaller and it can cause biodiversity to
decrease (Hudson et al. 2014; Uttara et al. 2012). Some studies have also
indicated that as land becomes more disturbed by human actions, the benefits that
we see from ecosystems shrink (Peng et
al. 2017).

            Epiphytes
are a group of organisms that live on trees and their presence and diversity
are important aspects of many ecosystems as they can affect different
developments and operations that take place in the ecosystems that they inhabit
(de la Rosa-Manzano et al. 2017; Einzmann
et al. 2016; Stanton et al. 2014). Some of the ecosystem
functions that epiphytes play a part in include the movement of both nutrients
and water (de la Rosa-Manzano et al.

2017; Stanton et al. 2014). Epiphytes
are also often used to gauge pollution levels as they are sensitive to changes
in the environment and they can take up pollutants (Becker et al. 2017). Human disturbance, which could include everything
from logging to pollution have a potential to have a large impact on the make
up of epiphyte species in more urbanized environments and if the diversity of
epiphytes is decreased, this could cause large problems for ecosystems around
the world (de la Rosa-Manzano et al.

2017; Becker et al. 2017; Stanton et al. 2014; Uttara et al. 2012; Werner and Robbert 2009; Werner 2011).

            Over
the past few years there have been several studies on epiphyte diversity in
urban environments and in environments that have been subject to human
disturbance (Becker et al. 2017; Werner
and Robbert 2009; Werner 2011). One study looked at how the composition of
epiphytes changes depending on how fractured the habitat is in order to see the
effects that humans can have on epiphyte species richness through taking away
habitat. They found that the trees on the boundary of the forest had a reduced
epiphyte species richness compared to the trees found within the forest (Werner
and Robbert 2009). They used this finding to demonstrate the effects that
humans breaking up habitats can have on epiphytes and their richness; human
effects have the potential to reduce epiphyte species richness (Werner and
Robbert 2009).

An additional
study that was conducted by Werner (2011) looked at the effect that cutting
down trees has on epiphyte diversity. Werner (2011) specifically looked at
epiphyte diversity on trees that had been left behind after clear-cutting and
that were confined from other trees. What this study discovered was that on
trees that were confined and left over from clear-cutting the epiphytes growing
on these trees showed diminished survival rates and diminished growth rates
when compared to trees from relatively intact forest and this suggests that
human disturbance had an unfavourable outcome on epiphyte composition (Werner
2011).

             Another
study looked at how the number of total epiphyte species and the amount of each
epiphyte species changed as the effects of urbanization got higher (Becker et al. 2017). They found the as
urbanization levels got higher, the total number of epiphyte species and the
total amount of each epiphyte species got lower (Becker et al. 2017). This suggested the urbanization had an adverse effect
on epiphyte composition (Becker et al.

2017).

            This
study aims to look at epiphyte diversity and how human disturbance can change
the diversity and composition of epiphyte communities. We looked at two
different sites, one urban and one natural, to see the impact that human
disturbance can have on epiphytes. This question has been looked at by other
researchers in several locations throughout the world, but it is important to
continue to study and look at how human disturbances can change epiphyte
composition at different locations throughout the world as other factors that
are maybe present in only certain locations may also help determine epiphyte
composition (Becker et al. 2017;
Werner and Robbert 2009; Werner 2011). In addition, continued monitoring of
epiphyte diversity is important as they contribute to the functions of
ecosystems as mentioned above (de la Rosa-Manzano et al. 2017; Stanton et al.

2014). Our main question was whether or not human disturbances would change the
diversity of epiphytes seen on trees. We hypothesized that the diversity of
epiphytes would be different between the urban and natural environments because
of the effects of human disturbances to the environment. Our prediction was
that the diversity of epiphytes would be higher in the natural environment,
which is subject to less human disturbance.  

 

 

 

 

Methods

 

Data
Collection

The goal of the
study was to compare differences in epiphyte diversity in urban and natural
environments and therefore the two study sites used represented each of these
categories. The urban site was located along the east side of Main Mall on the
UBC campus where rows of deciduous trees are present. The natural site was
located in Pacific Spirit Regional Park along the Sword Fern Trail and all
trees sampled were deciduous trees. The epiphytes observed were all identified
using an ID guide for local species of epiphytes. All epiphytes observed were
either lichens or mosses. The first step in measuring epiphyte diversity in
these two locations was to set up 50m transects along the ground. We then went
to one random point in each 10 m increment along the transect and found the
closest tree to that point which had a DBH of at least 20 cm. That means that
five trees were sampled for one 50 m transect. At those trees we set up
quadrats at 1.3 m from the ground using a tape measure and we sampled on the
north side of the tree for all samples. We determined the north side of the
tree using a compass app on our phones. The quadrats were divided into nine
equally sized squares. At each tree we identified which epiphytes were present
and what their relative abundances were by recording how many squares they were
present in from 1-9.

This process was
carried out twice as we collected pilot data to perform a power analysis. To
collect the pilot data we set out one 50 m transect at each site and therefore
collected a total of ten samples with a sample size of five for each site. The
described methods above were used to collect the pilot data data. The pilot
data was collected on October 23rd, 2017. Using G-Power and our
pilot data we calculated the sample size needed to achieve a power of 80% for
our study. G-Power calculated that in order to achieve a power of 80% we needed
a total sample size of 20 and a sample size of ten at each site. Therefore, for
our full data collection we used the same collection methods as described above
and as the ones used for our pilot data collection, but we laid down two 50 m
transects instead of one in order to increase the total sample size to 20. In
the natural environment the two transects were laid parallel to each other in
order to ensure that no trails were hit with the two transects. In the urban environment
we laid the two transects in series because if we laid them parallel we would
have had to sample on the other side of Main Mall and this could have greatly
changed the results because shade from buildings was different on either side.

The full data was collected on November 6th, 2017.     

 

Statistical
Analysis

            We
used R to do all of our statistical analysis. To compare diversity between the
forest and urban sites we used the Shannon-Wiener Index for both sites. We used
this index because it puts more stock into rare species and we wanted to
emphasize species richness in our analysis (Krebs 2015). To see if there was a
significant difference between the diversity of the two sites we used an ANOVA
test. A Rank-Abundance plot was created to give a visual demonstration of the
evenness of our abundance data. The next step involved creating a dissimilarity
matrix and to accomplish this we used the Horn Index. We used this index
because it can deal with relative abundances, which is what our data was, and
because it works well with smaller sample sizes (Krebs 2015). The last
statistical test performed was an ADONIS test to see if the difference between
the two sites was greater than the difference within the two sites. From the
dissimilarity values two other graphs were created, a cluster plot and an
ordination plot, as they helped to visualize the relationships between the
different sites. They were both used because the cluster plot helps to show
specific relationships between sites while the ordination plot gives a better
idea of how species composition looks between different sites as the species
are included on the plot.

 

 

Results

 

            When
comparing the Shannon-Wiener diversity values from the two sites using an ANOVA
test there was a significant difference between the two sites (one-way ANOVA, F=8.1925,
p=0.01036). The urban environment had a higher diversity value of 1.28
(SD of 0.24) and the natural environment had a lower diversity value of 0.92
(SD of 0.31).

            A
Rank-Abundance plot using a lognormal plot was created as seen in Figure 1. The lognormal plot was used
as it had the lowest AIC value by at least two compared to the other plot
options. In this plot the species of epiphyte with the highest abundance value
was the fluffy dust lichen and the species of epiphyte with the lowest
abundance was the shield lichen. It is also important to note that the
abundance numbers are actually the number of squares within quadrats that the
epiphytes were observed to be in as we did not count individuals.

Figure 1.

Rank-Abundance plot using the lognormal plot. This demonstrates the evenness of
the relative abundances of the epiphyte species. Fluffy dust lichen has the
highest abundance and the shield lichen has the lowest abundance.

 

            Using
the ADONIS and dissimilarity matrix to see if the difference between the two
sites was greater than the difference within the two sites, we found that the
difference between the two sites was larger than the difference within the two
sites as a significant p-value was obtained (ADONIS, F=12.77, p=0.0001).

Next, a cluster
plot was then created using the dissimilarity matrix as seen in Figure 2. In this plot sites 1-10 are
from the forest site and sites 11-20, which all make up one cluster together,
are from the urban environment. Because sites 11-20 make up one cluster that is
separate from the other 10 sites it seems that sites 11-20 are more similar to
each other than to any of the other sites.

 

Figure 2. This is
a cluster plot that was obtained using the Horn dissimilarity index to create a
dissimilarity matrix. Points 1-10 on the graph are sites from the natural
environment (Pacific Spirit Regional Park) and points 11-20 on the graph are
sites from the urban environment (Main Mall on the UBC campus).

 

Lastly, an
ordination plot was also created because, unlike the cluster plot, which shows
the clear lines and relationships between sites, it allows for a clear
visualization of what makes the sites different by including the species as well
as seen in Figure 3. Polygons were
added that help distinguish which location, either urban or forest, that the
sites are from. By looking at the plot you can see that the two polygons do not
overlap with each other.

 

 

Figure 3. This is
an ordination plot that was obtained using the Horn dissimilarity index to
create a dissimilarity matrix. Points 1-10 on the plot are sites from the
natural environment (Pacific Spirit Regional Park) and they are in the “Forest”
polygon on the left. Points 11-20 on the graph are sites from the urban
environment (Main Mall on the UBC campus) and they are in the “Urban” polygon
on the right.

 

 

Discussion

 

            The
question we were looking to answer was whether or not epiphyte diversity is
different between urban and natural environments due to human disturbance. We
hypothesized that there would be a difference of epiphyte diversity in these
two environments and we predicted that diversity would be higher in the natural
environment, which had experienced less human disturbance. From our results we
found that there was a significant difference in epiphyte diversity between the
urban and natural environments, but the direction of this difference was not
what we expected; the diversity of epiphytes was actually found to be higher in
the urban environment, which was the opposite of what we predicted. Comparing
the dissimilarity values of all of our samples also supported the result that
diversity was different between the two sites. From comparing these values we
saw that the difference between the sites was greater than the difference
within them and therefore there seems to be a distinct difference between these
two sites in regards to epiphyte composition. The cluster plot also shows how
the urban sites were all very similar in terms of their epiphyte composition,
which is likely why the ADONIS result was significant. The ordination plot also
confirms this with the polygons from the two locations showing no overlap; the
two locations are significantly different. This significant result was against
much of the research done on epiphyte diversity in urban environments and it
was against our prediction, but there are multiple reasons and multiple factors
that were present in this study that could have led to this interesting result (Becker
et al. 2017; Werner and Robbert 2009;
Werner 2011).

            Human
habitation of areas have been seen to have an impact on diversity and the
operations of ecosystems, but there are likely other important environmental
factors involved and one important one to epiphytes could be rainfall (Einzmann
et al. 2016; Hudson et al. 2014; Peng et al. 2017). One study found that rainfall plays a major role in
the epiphyte diversity seen in different human occupied areas in rural Panama
(Einzmann et al. 2016). This study is
interesting because it doesn’t only look at human effects, but also
environmental effects like rainfall, which play an important part in the
success of epiphytes (Einzmann et al.

2016). This could have helped explain our results as the rainfall levels seen
in Vancouver could help to make up for the negative effects of urbanization and
human disturbance and even out the playing field in terms of epiphyte
diversity. This same study also found that although areas of human occupancy
did show decreased species richness, the actual diversity of species per tree
was quite alike the diversity of species per tree seen in forests that have not
seen human occupancy (Einzmann et al.

2016). This shows that the relationship between human disturbance and epiphyte
diversity may not be as clear as you would expect (Einzmann et al. 2016).

Another article
discussed how different attributes of trees could be related to epiphyte
diversity (Izuddin and Webb 2015). This article states that epiphyte diversity
on trees is correlated with their size, or DBH, because of the greater surface
area of trees with a larger DBH, which creates a bigger area for epiphytes
species to encounter and become settled on the tree (Izuddin and Webb 2015).

Through observation in the field it seemed that the trees sampled along Main
Mall were larger than the trees sampled in Pacific Spirit National Park. The
larger size of the trees along Main Mall could potentially help explain why the
diversity was higher in the urban environment; their larger size allowed for
more space for the settling of epiphyte species (Izuddin and Webb 2015).

An interesting
abiotic factor may also play a part in the results we got for our experiment. A
study looking at the organization of epiphyte species along a tree found that
the partitioning of epiphytes on trees in the Pacific Northwest is associated
with the light gradient seen by the trees (McCune et al. 1997). The study found that certain epiphyte species were
often found at certain heights on a tree and they also found that this
organization of epiphytes seemed to be associated with different sectors of
light (McCune et al. 1997). They
explained that mosses tended to be found lower down on the trees and that
epiphytes tended to be found higher up on the trees (McCune et al. 1997). When comparing the urban
and natural environment in our study and in most scenarios, the natural
environment tends to have more canopy cover as more trees are present and
because of this there is a potential for more light to be present in the urban
environment. This could cause the light incline that is clear in a natural
forested environment to not be present in an urban environment; light is more
evenly distributed along a tree in the urban environment. Due to this light
incline being relatively absent in the urban environment it could potentially
cause the organization of epiphytes along a tree to not be as clear as it would
be in the forest as light is more available at all locations along the tree.

This could potentially allow epiphyte species to spread out more along a tree
and this could have been the case in our study. There may not have necessarily
been a higher species diversity in the urban environment that we tested, but
the epiphytes may have been more widespread on those trees due to more light
availability and because we only tested at one height we may not have had a
chance to detect as many species in the natural environment as they were
potentially organized due to light availability (McCune et al. 1997).        

            One
limitation of our study would be the fact that we only sampled at one height
for each tree. As mentioned above, in the forests of the Pacific Northwest
epiphytes show an organization along trees that may be correlated to light
availability and when you measure at only one height some species could be left
out, especially in the natural environment (McCune et al. 1997). Another limitation could have to do with how we
determined our urban and natural environments. We classified Pacific Spirit
Regional Park as a natural environment, but there is human traffic in that area
in the form of trails and there is a chance that this could possibly have an
effect on our results. Another factor that could have limited our study is that
for our power analysis we only looked to achieve 80% power. If we had increased
that number to gain more power it would have changed our sample size for the
full data collection and it could have possibly had ramifications for our
results.

            While
our results were not as expected, they help shed some light on what can change
the diversity of epiphytes and this important due to how they effect ecosystems
(de la Rosa-Manzano et al. 2017;
Stanton et al. 2014). Our results
could potentially demonstrate that there are many factors at play when
determining epiphyte diversity and that the idea that human disturbance has a
wholly negative effect may not necessarily be true in all situations (Einzmann et al. 2016; Izuddin and Webb 2015;
McCune et al. 1997). Our results may
also be the product of some limitations such as the lack of sampling at
different heights. Future studies on how human influences on light gradients
could affect epiphyte diversity and epiphyte organization along tress would
help shed further light on the multifaceted role humans play in determining the
overall diversity of epiphytes.