Ant Foraging and Climate Change

Ant Foraging and Climate Change July 2010 Ashley Jackson, John Collins, and Ngoc Thai One of the most prominent questions ants as an important part in future research we, as scientists and civilians, have is: in climate change. “What could happen to the world if the Fig. 1 The Lotka-Volterra competition equations are simple temperature rises overall during the next century?” What about the next decade? If we study the behavior of ant species model equations that show in a constant environment, throughout the country, we may discover an “complete competitors cannot coexist” (Hardin, Science, answer. Ants have been labeled by 1960). These equations were one of the first proposed models of competition between species. researchers as an indicator species because they are more susceptible to disturbance and However, there are many species that climatic change (Chapman and Bourke, EL, live in the same habitat and are able to 2001). An indicator species may act as an coexist. For example, ants have this ability. early warning to certain changes in the Within ant communities, ant species environment, whether natural or unnatural. compete for certain resources and niches. One key trait that makes ants a strong The idea of occupying niches (Grinnell, indicator species is their short life cycle. It is AUK, 1917) is one of the reasons competing much less time consuming to observe ant species are able to coexist in habitats. changes in a species that does not take years Another reason for this coexistence is trade- to start new generations. In addition to being offs between species. Many plants coexist named as an indicator species, ants have also through a competition/colonization trade-off been called a keystone species. A keystone (Hardin, Science, 1960). An example of species is a species that contributes to its trade-offs between ants is the fact that one environment in a way such that if it died, it species may be able to find food more would affect many different other species, quickly, but another species may be better at including plants. Ants are important for soil defending and displacing the other species turnover, litter processing and once they have found the food. Furthermore, decomposition (Holec and Frouz, one species may be able to forage at a higher Pedobiologia, 2005), and seed dispersal range of temperatures than another. This (Beattie, Cambridge Univ., 1985). For these particular trade-off is a major concern when reasons, it is imperative that we consider the issue of climate change arises. Climate

1 Ant Foraging and Climate Change July 2010 Ashley Jackson, John Collins, and Ngoc Thai 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 enough, it could lead to partial loss of biodiversity. Biodiversity is important to Fig. 3 A dominance-thermal tolerance trade-off curve maintain a natural balance in nature. In the (Lessard, Dunn, and Sanders, IS, 2009). figures below, each one represents a trade- off 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.

Fig. 2 This shows a dominance-discovery trade-off curve “No studies, to our knowledge, (Lebrun, JAE, 2007). have experimentally examined how projected temperature increases will affect ant 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

2 Ant Foraging and Climate Change July 2010 Ashley Jackson, John Collins, and Ngoc Thai mammoth and the saber-tooth tiger, as well as many other species. These losses have movement variation. A constant number of been accredited to the drastic climatic food pieces are dropped every morning. changes that occurred. At the same time, Food is also dropped throughout the day some species thrived during the Ice Age. It with a 0.1 chance every time step. The may prove beneficial to study which species probability that an ant will wait during a will be favored in the event that the time step depends on both temperature and temperature does increase. We may even be foraging success. If an ant has taken more able to provide theories and suggestions to than 10 consecutive moves without finding a help maintain as much biodiversity as piece of food, then the ant has a chance of possible. waiting depending on species and temperature. Ants will resume their normal There are many questions we could moving pattern when they find food. attempt to answer dealing with ants and Temperature and foraging rules affect both foraging success and foraging opportunities climate change. Our question, in particular: on a daily basis. The large-scale model How will climate change affect the contains more complicated rules and is run competition between hot-tolerant and cold- using MATLAB. Climate and food haul tolerant ants? We decided to use a multi- affect both colony success and reproduction scale, particularly a two-scale, model to on a monthly basis. Both of these models attempt to address this issue. Our model have their advantages. The small-scale consists of two parts, a small-scale and a model is mainly used for gathering statistics large-scale. The small-scale model contains and data points to construct various localized rules that are easily added and functions that are then used in the large- changed and is run using NetLogo. It is an scale model. The large-scale model will be agent-based model with two species of ants useful in gathering data for longer periods of competing for the same resources. It can test time, for instance hundreds of years, given different foraging rules such as ants waiting enough time. Within both models, we have under certain conditions. Rules include used only two different species for running speed, food specialization, and simplicity and time constraints; however, it

3 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 balance in favor of the hot tolerant ant species. Fig. 5 This shows the waiting probability of each ant 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.

4 Ant Foraging and Climate Change July 2010 Ashley Jackson, John Collins, and Ngoc Thai were able to produce a Haul Function, which is graphed below.

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

Fig. 12 This is the number of food pieces stored by species gathered from our small scale NetLogo model. A (hot-tolerant) at month i. All of the above are functions that were 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 the other. This is how we expect to propose

Fig. 15 The number of ants in species B at month i. theories as to what climate change may do to ant communities. Our future goals for this We did many runs to gather the data in the project include scaling the model up to 3000 graphs. The runs were done over the course ants, adding sensitivity analyses for of time that we spent once we had perfected parameters and initial conditions, and adding the large scale model. From the data stability analysis. gathered from the small scale model, we

5 Ant Foraging and Climate Change July 2010 Ashley Jackson, John Collins, and Ngoc Thai During the 8 week program at the conservation biology of social NIMBioS, we were able to determine a insects. Ecology Letters, 4: 650–662. problem, draw up a model, and propose  Holec, M. and Frouz, J. (2005), Ant possible outcomes for our problem. This (Hymenoptera: Formicidae) was done with the help of our advisors, Dr. communities in reclaimed and Sharon Bewick and Dr. Steven Wise. unreclaimed brown coal mining spoil Though, during the beginning, we met with dumps in the Czech Republic. our advisors 3-4 times a week, we quickly Pedobiologia, 49: 345-357. grew independent and began to work  Beattie, A. J. (1985), The amongst ourselves much more often. This evolutionary ecology of ant-plant program taught us many useful skills. mutualisms. Cambridge University Different educational backgrounds meant Press. that each moment, you could learn  Hardin, G. (1960), The Competitive something new that you did not come into Exclusion Principle the program knowing. We all learned from Science 131 (3409), 1292. each other. This made for a truly  Grinnell, J. (1917), The Niche- interdisciplinary and diverse learning Relationships of the California experience that will not soon be forgotten. Thrasher. The Auk, 34: 427-433.

Acknowledgements:  LEBRUN, E. G. and FEENER, D. H. (2007), When trade-offs interact: We would like to thank the National Institute balance of terror enforces dominance for Mathematical and Biological Synthesis, the discovery trade-off in a local ant University of Tennessee at Knoxville, and our assemblage. Journal of Animal advisors, Sharon Bewick and Steven Wise. Each Ecology, 76: 58–64. party played a critical role in the success of our  Lessard, J. –P., Dunn, R. R., and summer research program. Sanders, N. J., (2009), Temperature- References: mediated coexistence in temperate

 Chapman, R. E. and Bourke, A. F. G. forest ant communities. Insectes (2001), The influence of sociality on Sociaux, 56: 149-156.

6 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): 4765- 4769.