Download Salamander Competition Research Paper

Effects of Competition on Ambystoma Salamander Larvae
Erica Reed
April 28, 2006
BIO 299
High Point University
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ABSTRACT: Competition is one of the leading factors in the survival and
development of almost all species on earth. Every living thing is affected in some
way or another by competition, whether it is interspecific or intraspecific.
Ecologists have been studying the effects of competition for a number of years
trying to determine what effects the growth and development of a species.
Competition can change the appearance, behavior, and activity levels of Ambystoma
salamander larvae. Field observations serve as the most reliable source of
information when documenting the effects of competition on a species. Natural
areas are divided into quadrants to test different treatments. The aim of this paper
is to examine the effects of interspecific and intraspecific competition that affects
Ambystoma salamander larvae as discussed in a various amount of sources.
The larval stage of most organisms is the most crucial time for development and will
indicate the chance of survival for the organism in the future. Larval salamanders are no
different. This paper addresses the aspects of intraspecific and interspecific competition of
Ambystoma salamander larvae. The objective of this paper is to determine which has a greater
effect, if one does, in fact, have a greater effect. To understand the role of competition in the
growth and survival of salamander larvae, one must understand how Ambystoma larvae live in
the natural world.
Ambystoma salamanders are commonly found in temporary woodland ponds. Most of
the studies I reviewed were completed in the Piedmont of North Carolina or in woodland areas
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with climates and environmental conditions very similar to those found in the Piedmont of North
Carolina. The breeding time is from September to November, the ponds where eggs are
deposited fill between November and January, and the larval period lasts from 4 to 5 months
(Smith, 1990). Eggs are attached to fallen branches that may have fallen in to the pond. These
eggs have a jelly coat on them and can be clear or a milky white color.
The competitive ability is determined by a combination of necessary food requirements
and foraging ability. Ambystoma salamanders are gape-limited predators. This means that they
are only able to feed on organisms that they are able to fit in their mouth at one time. They are
also considered generalist foragers, which means they are able to utilize a various amount of
food items. The types of food items included in their diet are macroinvertebrates, isopods,
aquatic insects, and in some cases other amphibian larvae (Smith, 1990).
Ambystoma salamanders are also capable of phenotypic plasticity, a change in which an
organism activates different phenotypes in response to its environment. It is an evolved
characteristic that increases the individuals’ chance of survival.
Most of the experimental methods to observe the effects and causes of competition in
larval salamanders include a tremendous number of field observations and laboratory set ups. In
the field, most of the study area consists of temporary ponds that are divided in to quadrants to
test different treatments and effects of different variables. These areas tend to be blocked off by
semi permeable barriers that allow water and macroinvertebrates or other small food sources to
flow through.
The effects of intraspecific competition can be seen and measured in Ambystoma
salamander larvae. Intraspecific competition is competition between individuals of the same
species. Intraspecific competition effects not only the survival of larvae, but it has an effect on
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the larval size, aggression, foraging ability, and prey availability. When species coexist they
develop different ways to deal with their environment and life cycles to attempt to avoid
competition. Ambystoma salamanders do the same. They are different in the time they lay their
eggs and in hatch time. They are able to change their development time to avoid competition to
the best of their ability. The difference in growth time may be what eventually leads to
intraguild predation, which is predation within the species (Brodman, 2004).
When size is thought of in terms of competition, one may assume that bigger is better.
This is reflected in the instance of Ambystoma salamander larvae. Smith (1990) found that
variation in size may be reflective of competition in which larger individuals negatively affect
smaller individuals by their ability to better obtain food resources, even those that may be
limited. Energy requirements may be where the advantage to being small comes in. Smaller
individuals require less energy so they are able to use limited resources more efficiently than
larger individuals.
Larger individuals require more to meet their energy demands and that causes an increase
in interference competition. In interference competition, the individuals have contact with each
other. Larger sized salamanders are able to use their size to their advantage and are able to
obtain more food material than the smaller individuals if there is actual contact and interference
competition. Larger larvae show greater signs of aggression when competing for food and they
are able to use their size to their advantage in these situations (Smith, 1990). For the most part,
size differences affect competition through interference and not through feeding rates. It is the
size difference, if it is great enough, that may result in cannibalism and intraguild predation
within the Ambystoma salamander larvae (Pearman, 2002).
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Smaller individuals are superior in the aspect of exploitative competition. Exploitative
competition is where individuals compete with each other for resources and do not have any
physical contact. However, through many experiments, size is not seen to be dependent in
exploitative competition (Smith, 1990). It is due to the lack of resources and the smaller
individual’s ability to obtain the resources, that through exploitative competition, the smaller
individual may prosper.
Aggression is a common component of foraging and living within a species for which
intraspecific competition is addressed. Aggression is a form of direct interference experienced
within a species. One individual becomes aggressive towards another to increase its chance of
survival and increase its intake of nutrients. Johnson et al (2003) observed aggressive behavior
as two types, a lunge and a bite. A lunge is simply advancement by an individual towards
another individual and a bite is what it implies, with an open mouth grabs another individual.
Lunging occurred most in experimental observations.
Experimentation has shown that when larvae of different sizes exist together in a given
area, smaller larvae are negatively affected and attacked more often due to aggressive
interactions with larger larvae. This interference can reduce growth rate of smaller individuals.
Aggressive behavior leads to injury of certain individuals and is often the first step to
cannibalism. Cannibalism is rarely seen in Ambystoma salamander larvae, but is not unheard of.
Larger larvae will indeed eat smaller larvae if food resources are low and the opportunity
presents itself.
Johnson et al (2003) observed that more aggression is observed during feeding than
before feeding. There is a direct interference competition for food resources by the larger larvae.
Food resources tend to act as a cue for aggressive behavior.
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Intraguild predation and cannibalism are two components of density-dependent
population regulation. Both of these components increase when density increases. Buskirk and
Smith (1991) found that Ambystoma salamander larvae populations at high densities experience
reduced individual performance. This is a result of competition for limited resources or
interference competition, such as cannibalism or physical competition for feeding sites. High
densities also reduce growth rates and lengthen exposure to predators that may be around.
Increased densities in the larval population increase mortality.
Along with intraspecific competition, interspecific competition plays an equal role in
affecting the survivorship of Ambystoma salamander larvae. Interspecific competition refers to
the competition, whether it is by direct interference or exploitative use of the same resources,
between different species. There are many different species of organisms that live in the same
habitat and affect the salamander larvae. Trout and other fish, wood frog (Rana sylvatica)
tadpoles, and even some aquatic insects have negative and some positive effects on salamander
larvae.
Tyler et al (1998) surveyed high-elevation lakes in northwestern United States to
determine the effect of trout on Ambystoma salamander larvae. Trout are not normally found in
these areas. They have been introduced into the habitat where Ambystoma salamanders have
lived. The main discoveries Tyler et al (1998) made were that trout, as well as other fish, can
reduce or even eliminate Ambystoma larvae. The presence of trout may also inhibit growth,
reduce survival, and decrease activity. Predation by fish is likely the reason for decrease in
abundance of Ambystoma salamander larvae found in high-elevation lakes. The interaction
between trout and salamander larvae were seen to cause a shift in larval behavior. The
salamander larvae shifted from day feeding to nocturnal activity. They tend to hide during the
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day and forage at night to avoid predation. The shift in foraging behavior causes a decrease in
the amount of food consumption and decreases foraging efficiency.
Holbrook and Petranka (2004) determined that the tadpoles of Rana sylvatica (wood
frogs) may have a greater effect on Ambystoma salamander larvae. Rana sylvatica tadpoles are
known to feed on the eggs of Ambystoma salamanders and even eat exposed embryos. The risk
of predation is high for salamander larvae in the presence of Rana sylvatica tadpoles.
Salamander larvae have not been seen feeding on tadpoles, possibly due to the gape limitations.
This shows that the predation and interaction seem to favor the wood frog tadpoles.
The outer coats of most salamander eggs are jelly that contain high amounts of water and
the algae that grows on them provides a lot of needed nutrients to the wood frog tadpoles.
Petranka et al (1998) observed that the clear egg masses seem to be more vulnerable to
predation, although the reason has not been determined. For the most part the wood frog
tadpoles feed on the jelly coat that surrounds the salamander embryos. The jelly coat is slowly
removed and embryos are exposed. That is the occasion in which wood frog tadpoles may feed
on the embryos.
According to Petranka et al (1998), the wood frog tadpoles do not intentionally seek out
the salamander egg masses as a food source. Times when food resources are low are when egg
predation is observed the most. This leads to the assumption that egg predation is mediated by
the total amount of food available. Low food resource availability causes an increase of egg
predation that leads to an increase in salamander larvae mortality.
The wood frog tadpoles have an effect on the growth, time of metamorphosis, and
survival of salamander larvae. The predation on eggs leads to these effects. Even with egg
predation, hatching time is not affected by the wood frog tadpoles. Development may however
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be affected. The tadpoles could negatively affect the larvae developmentally by tearing away the
jelly coat around the embryos leaving them vulnerable to environmental conditions. This is a
negative effect on the growth and development of the larvae. Tadpoles can also affect the larvae
by causing them to begin metamorphosis at a much sooner time to avoid predation and the
negative effects of the environment.
Metamorphosis time is affected in two different ways. In environments where wood frog
tadpoles have been removed, metamorphosis occurs earlier than in environments where wood
frog tadpoles are present. Some salamander larvae had delayed metamorphosis in the presence
of wood frog tadpoles. However, delaying metamorphosis is dangerous to salamander larvae
due to the possibility that temporary ponds in which they are living in will dry while they are still
larvae (Holbrook and Petranka, 2004).
Wood frog tadpoles also eat much of the same food resources as the larval salamanders.
Both eat macroinvertebrates and some aquatic insects. This causes an exploitative interaction for
food. This is another form of interspecific competition rather than direct interference. The
overall survival of salamander larvae is influenced by the presence or absence of wood frog
tadpoles. Survival rates were found to be higher in environments that lack wood frog tadpoles.
Basically, higher densities of wood frog tadpoles decreased the chance of survival, growth, and
development of many Ambystoma larval salamanders.
Along with trout and wood frog tadpoles, aquatic insects play a key role in competition
with larval salamanders. Although some salamanders eat aquatic insects, two aquatic insects
have an effect on survival and evolution of salamander larvae. The two aquatic insects are the
larval stages of the diving beetle and dragonfly. Both are commonly found in areas where
salamander larvae live and play a crucial role in competition.
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Dragonfly larvae are sit and wait predators. They stay in one place and ambush their
prey. Diving beetles are more actively chase their prey. Storfer and White (2004) found that
both, the dragonfly larvae and diving beetle larvae, have different effects on the evolution of
traits that are seen in many larval salamanders when in an area with a predator than in a control,
with out predators.
Storfer and White (2004) observed that in environments with the dragonfly larvae,
salamanders have shorter snout vents. They are also have shorter and deeper tails which allow
for a more rapid burst of speed and faster swimming to escape predators, such as the dragonfly
that sits and waits to attack. The salamander larvae also weigh less in environments with the
dragonfly larvae. This weight difference is due to the salamander larvae attempting to avoid
predation by hiding in areas with little food availability.
Storfer and White (2004) also observed that in environments with diving beetle larvae,
shorter snout vents are seen. In this case, the salamander larvae had longer tails that were also
deep, which allows for extended swim time and made the swimming more efficient to escape the
active predator. The salamander larvae in areas with the diving beetles weighed more than the
salamander larvae in the dragonfly environment, but less than the salamanders in the control
environment that was predator free.
The longer tail lengths, that were observed in the presence of the diving beetle larvae,
reduce turbulence which can decrease an individual’s risk of being a detected by a predator. The
longer tail also provides a greater surface area for a predator to bite in an attack or during direct
interference competition. This limits the amount of bites and attacks that are lethal. It gives the
salamander larvae an opportunity to get away and the tail is able to regenerate itself (Yurewicz,
2004).
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Many things affect the survivorship of Ambystoma salamander larvae. The most
common is competition. It is hard to determine which form of competition has the greatest
impact, but both interspecific and intraspecific competitions are critical. The effects of
interspecific competition seem to be more important and affect the salamander larvae to a greater
extent. This leads to the assumption that interspecific competition has the greatest impact.
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References
Brodman, R. 2004. Intraguild predation on congeners affects size, aggression, and
survival among Ambystoma salamander larvae. Journal of Herpetology, 38: 21-26.
Holbrook, C.T. and J.W. Petranka. 2004. Ecological interactions between Rana
sylvatica and Ambystoma maculatum : Evidence of interspecific competition and
facultative intraguild predation. Copeia, 4: 932-939.
Johnson, E.B., P. Bierzychudek, and H. Whiteman. 2003. Potential of prey size
and type to affect foraging asymmetries in tiger salamander (Ambystoma tigrinum
nebulosum) larvae. Canadian Journal of Zoology, 81: 1726-1735.
Pearman, P.B. 2002. Interactions between Ambystoma salamander larvae:
Evidence for competitive asymmetry. Herpetologica, 58: 156-165.
Petranka, J.W., A.W. Rushlow, and M.E. Hopey. 1998. Predation by tadpoles of Rana
sylvatica on embryos of Ambystoma maculatum: Implications of ecological role
reversals by Rana (predator) and Ambystoma (prey). Herpetologica, 54: 1-13.
Smith, C.K. 1990. Effects of variation body size on intraspecific competition
among larval salamanders. Ecology, 71: 1777-1788.
Storfer, A. and C. White. 2004. Phenotypically plastic responses of larval tiger
salamanders, Ambystoma tigrinum, to different predators. Journal of Herpetology, 38:
612-615.
Tyler, T., W. Liss, L. Ganio, G. Larson, R. Hoffman, E. Deimling, and G. Lomnicky.
1998. Interaction between introduced trout and larval salamanders (Ambystoma
macrodactylum) in high-elevation lakes. Conservation Biology,
12: 94-105.
Van Buskirk, J. and D.C. Smith. 1991. Density-dependent population regulation in a
salamander. Ecology, 72: 1747-1756.
Yurewicz, K. 2004. A growth/mortality trade-off in larval salamanders and the
coexistence of intraguild predators and prey. Oecologia, 138: 102-111.
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Effects of intraspecific and interspecific competition on
larval Ambystoma salamanders
I.
Introduction
A. What role does intraspecific and interspecific competition play on
the survival and growth of larval Ambystoma salamanders?
II.
Intraspecific Competition
A. Size
B. Aggression
C. Foraging abilities
D. Overall survival impact
III.
Interspecific Competition
A. Trout
B. Effect of Wood Frog (Rana sylvatica) tadpoles
1. Growth
2. Time of metamorphosis
3. Survival
C. Aquatic Insects
1. Dragonfly naiads
2. Diving Beetle larvae
IV. Conclusion
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