Download Amphibian Visual Encounter Survey Luke Haupt WFS 310 10/7/08

Amphibian Visual Encounter Survey
Luke Haupt
WFS 310
10/7/08
Introduction –
In this exercise a visual encounter survey (VES) was performed to determine the number
of species and their density along Mount Nittany. A VES is a scan search used to determine
species diversity and population density which works well for terrestrial amphibians, so it works
well for this study. The VES works on four assumptions: 1) Every individual has an equal
chance of being counted during the survey, 2) Each species is equally likely to be observed
during each sampling session, 3) Each individual is only counted once, and 4) results from two
or more observers surveying the same area simultaneously are identical. This type of survey is
very easy and simple, and for the purposes of this study, it is accurate and the assumptions are
realistic.
The reason for this particular survey is to learn the visual encounter survey technique,
and to provide the Mount Nittany Preserve board with a list of the species found.
Methods and Materials –
For this study a compass was needed to extract our bearings as transects were set up, as
well as a loggers tape so that the 20 meter transects could be measured out. A watch was used to
track the amount of time spent at each transect, and Ziploc bags were used to keep the
salamanders in once they were caught so that they did not dry out or overheat from being
handled. (Grant 2008)
Once the destination of Mount Nittany was reached, a starting spot along the trail was
designated. Once the location of the first transect was reached, the tape was used to measure 20
meters off the trail, and the transect was perpendicular to the trail. The transect included the 20
meters of tape as well as one meter on either side of the tape, so that the transect was 40 square
meters. The times were recorded so that the number of individuals and/or species per person
hours could be determined. (Grant 2008)
Once the transects were laid out, all group members turned over all logs and rocks within
the transect in order to find any amphibians or reptiles. Any that were caught were put into a
Ziploc bag and identified, then released back where they were found, next to the rock or log they
were found under so that no harm would be done to the animal. (Grant 2008)
After each transect, the group would go twenty paces past the last group along the trail
and repeat this process again. Seven transects were done for a total of 280 square meters
surveyed. (Grant 2008)
Results –
Table 1: The table below shows each
individual that was captured on each transect.
Transect
Number
Compass
Bearing
1 128 degrees
2 86 degrees
3 142 degrees
4 136 degrees
5 118 degrees
5 118 degrees
6 140 degrees
7 128 degrees
Time
Time
Start
End
Species Caught
11:56 12:06 none
12:09 12:15 none
Plethodon
12:17 12:22 cinereus
Plethodon
12:28 12:33 cinereus
Plethodon
12:36 12:41 cinereus
Plethodon
12:36 12:41 glutinosus
Bofu
12:44 12:48 americanus
Bofu
12:57
1:01 americanus
Time of
Capture
n/a
n/a
Found
Under:
n/a
n/a
12:18 rock
12:30 rock
12:38 rock
Notes
lead back
phase
lead back
phase
lead back
phase
12:38 rock
12:47 log
1:00 rock
large
female
male
Species richness is equal to the total number of species found in the plot, so for this study,
the species richness is three. After the species richness is known, the proportion of individuals
per species is found. The total number of individuals is six. P. cinereus had three individuals, so
their proportion was 3/6 or .500, the proportion of B. americanus was 2/6, or .333, and P.
glutinosis was 1/6, or .167. These numbers are important because they represent pi in the
Shannon’s Index of Diversity equation.
The Shannon’s Index of Diversity equation is below:
H’ = - ∑ pi ln pi
H’ is the Shannon’s Index of Diversity
pi is the proportion of each species that was determined above
ln is simply the natural log
After performing the equation the Shannon Index of Diversity comes to 1.012. This
number will be needed to calculate species evenness through the following equation:
EH = H’ / H’max
EH is the evenness
H’ is the Shannon Index of Diversity
H’max is the natural log of the species richness, which is three in this case
After performing this equation, the species evenness is found to be 0.9208.
The time spent searching is measured in person hours. This is found by taking the total
time spent searching and multiplying it by the number of people in the group. In this study four
people searched for a total of 39 minutes, 4 times 39 is 156 minutes, or 2.6 person hours.
Discussion –
The species evenness came out to be 0.9208. This number is good because when that
number gets closer to one, it indicates that there are equal numbers of species present, whereas if
the number gets closer to zero, that means that there is a lot of one species, but almost none of
others.
The VES study is an efficient study for what was needed to be done. A drift fence could
have been set up, but that would have taken more time, plus the captured organisms may have
gotten eaten by another animal that may have also been trapped. Toe-clipping could also have
been done, and then the next day another survey could have been done to see what ones were
recaptured. However, this technique is much more invasive than the VES, and many of the
salamanders were fairly tiny, so trying to clip a toe would be incredibly pain-staking.
Salamanders also don’t make any noise, so acoustic sampling is also out of the question.
Through this study three species of amphibians were found: Plethodon cinereus (redbacked salamander), Plethodon glutinosus (slimy salamander), and Bofu americanus (American
toad).
The red-backed salamander is one of the most abundant vertebrates in North America’s
moist temperate forests with their population density sometimes exceeding 1-2 individuals per
square meter. They are restricted to cool, moist habitats under logs and other woody debris, as
well as under rocks and in burrows, so these salamanders will be found in mature forests. Clear-
cut forests many times show localized extirpations of these organisms, although they usually
recover eventually. (Riedel, Russel, et. al. 2007)
The slimy salamander is another terrestrial salamander that was found in our transects.
This salamander secretes a lot of glue-like slime when handled.
A study was done on competition between the slimy and red-backed salamanders to see if
the size of the species affected the competition between them. In their study they put juvenile
red-backs with juvenile slimy salamanders plus a large adult slimy salamander. The result was
that the growth of red-backs was restricted, but no more than it was when the only competition
was amongst themselves. In their second experiment, they paired adult red-backs with slimy
salamanders of smaller, similar, and larger sizes. The results were the same as the first
experiment, growth was restricted but it had nothing to do with the size of the species. (Price,
Shields, 2002)
The American Toad was another species that was observed on Mount Nittany. The
American toad belongs to the genus Bufonidae. An interesting study found that this genus
originated in South America. The people who performed this study looked at 2521 base pairs of
DNA including mitochondrial DNA to determine the origin of true toads. (Pramuk, et. al.)
Visual encounter surveys are not just used for terrestrial amphibians, even though they
work best for them. They have been used along with acoustic encounter surveys to see if there is
a correlation between the results of the two. The study found that their results varied with the
time of day and year, and with the region. The encounter rate visually was a little over 2 whales
per hour, while whales encountered singing or calling was less than one per hour. A positive
correlation was found between whales calling and whales seen, but no correlation was found
between whales singing and whales seen. (Olsen, et. al., 2007)
The study with the whales brings up a good idea for another experiment, another study
could be performed to see if there is a correlation between frog heard and frogs seen to compare
the results.
References –
“Habitat relationships of eastern red-backed salamanders (Plethodon cinereus) in Appalachian
agroforestry and grazing systems,” Breanna L. Riedel, Kevin R. Russell, W. Mark Ford,
Katherine P. O’Neill and Harry W. Godwin, AGRICULTURE ECOSYSTEMS &
ENVIRONMENT Volume: 124 Issue: 3-4 Pages: 229-236 Published: APR 2008, College
of Natural Resources, University of Wisconsin-Stevens Point, Stevens Point, WI 54481, USA
USDA Forest Service, Northern Research Station, Parsons, WV 26287, USA USDA Agricultural
Research Service, Appalachian Farming Systems Research Center, Beaver, WV 25813, USA
Received 16 February 2007; revised 3 October 2007; accepted 4 October 2007. Available
online 19 November 2007.
“SIZE-DEPENDENT INTERACTIONS BETWEEN TWO TERRESTRIAL AMPHIBIANS,
PLETHODON CINEREUS AND PLETHODON GLUTINOSUS,” Jennifer E. Price and Jennifer
A. Secki Shields, Volume 58, Issue 2 (June 2002), Mountain Lake Biological Station and
Department of Biology, University of Virginia, Gilmer Hall, Charlottesville, VA 22903, USA
“Around the world in 10 million years: biogeography of the nearly cosmopolitan true toads
(Anura: Bufonidae),” Jennifer B. Pramuk, Tasia Robertson, Jack W. Sites Jr and Brice P.
Noonan, Global Ecology and Biogeography Volume 17 Issue 1, Pages 72 – 83 Published Online:
16 Aug 2007 Journal compilation © 2008 Blackwell Publishing, Department of Herpetology,
Bronx Zoo/ Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, USA,
Brigham Young University, Department of Integrative Biology, Provo, UT 84602, USA, Duke
University, Department of Biology, Durham, NC 27708, USA
“Blue whale visual and acoustic encounter rates in the southern California bight,” Oleson EM
(Oleson, Erin M.), Calambokidis J (Calambokidis, John), Barlow J (Barlow, Jay), Hildebrand JA
(Hildebrand, John A.), MARINE MAMMAL SCIENCE Volume: 23 Issue: 3 Pages: 574597 Published: JUL 2007
Grant, Jacqualine, “WFS 310 – Wildlife & Fisheries Measurements – Lab Four, 2008,
Amphibian Visual Encounter Survey,” Fall 2008, College of Agricultural Sciences, Penn State
University, University Park, Pennsylvania, 16802, USA