Ant Foraging and Climate Change
July 2010
Ashley Jackson, John Collins, and Ngoc Thai
One of the most prominent questions
reasons, it is imperative that we consider
we, as scientists and civilians, have is:
ants as an important part in future research
“What could happen to the world if the
in climate change.
temperature rises overall during the next
century?” What about the next decade? If
we study the behavior of ant species
throughout the country, we may discover an
answer. Ants have been labeled by
researchers as an indicator species because
Fig. 1 The Lotka-Volterra competition equations are simple
model equations that show in a constant environment,
“complete competitors cannot coexist” (Hardin, Science,
1960). These equations were one of the first proposed
models of competition between species.
they are more susceptible to disturbance and
climatic change (Chapman and Bourke, EL,
2001). An indicator species may act as an
early warning to certain changes in the
environment, whether natural or unnatural.
One key trait that makes ants a strong
indicator species is their short life cycle. It is
much less time consuming to observe
changes in a species that does not take years
to start new generations. In addition to being
named as an indicator species, ants have also
been called a keystone species. A keystone
species is a species that contributes to its
environment in a way such that if it died, it
would affect many different other species,
including plants. Ants are important for soil
turnover, litter processing and
decomposition (Holec and Frouz,
Pedobiologia, 2005), and seed dispersal
(Beattie, Cambridge Univ., 1985). For these
However, there are many species that
live in the same habitat and are able to
coexist. For example, ants have this ability.
Within ant communities, ant species
compete for certain resources and niches.
The idea of occupying niches (Grinnell,
AUK, 1917) is one of the reasons competing
ant species are able to coexist in habitats.
Another reason for this coexistence is tradeoffs between species. Many plants coexist
through a competition/colonization trade-off
(Hardin, Science, 1960). An example of
trade-offs between ants is the fact that one
species may be able to find food more
quickly, but another species may be better at
defending and displacing the other species
once they have found the food. Furthermore,
one species may be able to forage at a higher
range of temperatures than another. This
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Ant Foraging and Climate Change
July 2010
Ashley Jackson, John Collins, and Ngoc Thai
particular trade-off is a major concern when
the issue of climate change arises. Climate
change may favor one species over another.
If this happens, certain niches may be left
unoccupied. If the newly unoccupied niche
is one that impacts humans or closely
enough, we may be affected in ways that
could change our everyday comfort in life. If
the extinction of certain species is drastic
Fig. 3 A dominance-thermal tolerance trade-off curve
enough, it could lead to partial loss of
(Lessard, Dunn, and Sanders, IS, 2009).
biodiversity. Biodiversity is important to
maintain a natural balance in nature. In the
figures below, each one represents a tradeoff curve. There is also a graph that shows
loss of biodiversity by means of a species
dying out.
Fig. 4 This graph is merely a cartoon of what could happen
over time. It is in no way an actual representation of any
proven data.
“No studies, to our knowledge, have
experimentally examined how projected
temperature increases will affect ant
Fig. 2 This shows a dominance-discovery trade-off curve
(Lebrun, JAE, 2007).
communities and the functions they
provide,” (Sanders et al., in press).
However, at the end of the Ice Age, we were
left with the extinctions of the woolly
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Ant Foraging and Climate Change
July 2010
Ashley Jackson, John Collins, and Ngoc Thai
mammoth and the saber-tooth tiger, as well
movement variation. A constant number of
as many other species. These losses have
food pieces are dropped every morning.
been accredited to the drastic climatic
Food is also dropped throughout the day
changes that occurred. At the same time,
with a 0.1 chance every time step. The
some species thrived during the Ice Age. It
probability that an ant will wait during a
may prove beneficial to study which species
time step depends on both temperature and
will be favored in the event that the
foraging success. If an ant has taken more
temperature does increase. We may even be
than 10 consecutive moves without finding a
able to provide theories and suggestions to
piece of food, then the ant has a chance of
help maintain as much biodiversity as
waiting depending on species and
possible.
temperature. Ants will resume their normal
There are many questions we could
attempt to answer dealing with ants and
climate change. Our question, in particular:
How will climate change affect the
competition between hot-tolerant and coldtolerant ants? We decided to use a multiscale, particularly a two-scale, model to
attempt to address this issue. Our model
consists of two parts, a small-scale and a
large-scale. The small-scale model contains
localized rules that are easily added and
changed and is run using NetLogo. It is an
agent-based model with two species of ants
competing for the same resources. It can test
different foraging rules such as ants waiting
under certain conditions. Rules include
running speed, food specialization, and
moving pattern when they find food.
Temperature and foraging rules affect both
foraging success and foraging opportunities
on a daily basis. The large-scale model
contains more complicated rules and is run
using MATLAB. Climate and food haul
affect both colony success and reproduction
on a monthly basis. Both of these models
have their advantages. The small-scale
model is mainly used for gathering statistics
and data points to construct various
functions that are then used in the largescale model. The large-scale model will be
useful in gathering data for longer periods of
time, for instance hundreds of years, given
enough time. Within both models, we have
used only two different species for
simplicity and time constraints; however, it
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Ant Foraging and Climate Change
July 2010
Ashley Jackson, John Collins, and Ngoc Thai
is tractable to add more species to create a
more realistic model.
Fig. 7 A gradual change in yearly temperature tips the
Fig. 5 This shows the waiting probability of each ant
balance in favor of the hot tolerant ant species.
species dependent upon temperature ranges.
We managed to gather and plot the
population data for constant yearly
temperature, gradually changing yearly
temperature, and rapidly changing yearly
temperature. The following figures represent
those plots, respectively.
Fig.
8
Rapidly
changing
yearly
temperature
first
significantly favors the cold tolerant ants. After the
temperature reaches about 30 degrees, there isn’t a very
significant difference in each species.
The data gathered was the result of the
following functional forms that appeared in
our MATLAB model.
Fig. 6 With no change in yearly average temperature, both
species stay proportional.
Fig. 9 This is the function that represents the death that
occurs in the model.
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Ant Foraging and Climate Change
July 2010
Ashley Jackson, John Collins, and Ngoc Thai
Fig. 10 This function represents how much energy it costs
to move, metabolism (Lighton and Bartholomew, PNAS,
1988).
Fig. 11 This function represents the reproduction and when
it occurs.
Fig. 5 The haul function was a direct result of the data
gathered from our small scale NetLogo model.
Fig. 12 This is the number of food pieces stored by species
All of the above are functions that were
A (hot-tolerant) at month i.
determined by analyzing the statistics we
collected while doing runs using the small-
Fig. 13 The number of food pieces stored by species B
scale model. These functions were then
(cold-tolerant) at month i.
placed into the large-scale model to graph
surface plots. Using the different foraging
Fig. 14 The number of ants in species A at month i.
rules,
we
were
able
to
manipulate
circumstances that favored one species over
Fig. 15 The number of ants in species B at month i.
We did many runs to gather the data in the
graphs. The runs were done over the course
of time that we spent once we had perfected
the large scale model. From the data
gathered from the small scale model, we
were able to produce a Haul Function, which
is graphed below.
the other. This is how we expect to propose
theories as to what climate change may do to
ant communities. Our future goals for this
project include scaling the model up to 3000
ants,
adding
sensitivity
analyses
for
parameters and initial conditions, and adding
stability analysis.
During the 8 week program at
NIMBioS, we were able to determine a
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Ant Foraging and Climate Change
July 2010
Ashley Jackson, John Collins, and Ngoc Thai
problem, draw up a model, and propose
the conservation biology of social
possible outcomes for our problem. This
insects. Ecology Letters, 4: 650–662.
was done with the help of our advisors, Dr.

Holec, M. and Frouz, J. (2005), Ant
Sharon Bewick and Dr. Steven Wise.
(Hymenoptera: Formicidae)
Though, during the beginning, we met with
communities in reclaimed and
our advisors 3-4 times a week, we quickly
unreclaimed brown coal mining spoil
grew independent and began to work
dumps in the Czech Republic.
amongst ourselves much more often. This
Pedobiologia, 49: 345-357.
program taught us many useful skills.

Beattie, A. J. (1985), The
Different educational backgrounds meant
evolutionary ecology of ant-plant
that
mutualisms. Cambridge University
each
moment,
you
could
learn
something new that you did not come into
the program knowing. We all learned from
each
other.
This
interdisciplinary
made
and
for
diverse
a
Press.

truly
Exclusion Principle
learning
experience that will not soon be forgotten.
Hardin, G. (1960), The Competitive
Science 131 (3409), 1292.

Grinnell, J. (1917), The NicheRelationships of the California
Acknowledgements:
Thrasher. The Auk, 34: 427-433.
We would like to thank the National Institute

for Mathematical and Biological Synthesis, the
LEBRUN, E. G. and FEENER, D. H.
(2007), When trade-offs interact:
University of Tennessee at Knoxville, and our
balance of terror enforces dominance
advisors, Sharon Bewick and Steven Wise. Each
discovery trade-off in a local ant
party played a critical role in the success of our
assemblage. Journal of Animal
summer research program.
Ecology, 76: 58–64.
References:

Chapman, R. E. and Bourke, A. F. G.
(2001), The influence of sociality on

Lessard, J. –P., Dunn, R. R., and
Sanders, N. J., (2009), Temperaturemediated coexistence in temperate
forest ant communities. Insectes
Sociaux, 56: 149-156.
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Ant Foraging and Climate Change
July 2010
Ashley Jackson, John Collins, and Ngoc Thai

Lighton, J. R. B. and Bartholomew,
G. A., (1988), Standard energy
metabolism of a desert harvester ant,
Pogonomyrmex rugosus: Effects of
temperature, body mass, group size,
and humidity. PNAS 85 (13): 47654769.
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