Fire Ant Population Model

Parameter Estimating and Model Development

The fire ant model would be developed following the object-oriented paradigm used in our Africanized and European honey bee model (Makela et al. 1993a, b, Rowell et al. 1993), but would be structured to capture a greater degree of inter- and intra-colony dynamics.  An appropriately structured objected-oriented model can simulate the within-colony and between-colony dynamics in a heterogeneous environment,  simulate the movement and behavior of individual workers, reproductives, and colonies, and can predict the spatial patterns of colonies and host resources.

Because of its ability to capture the mechanistic basis for complex biological processes, individual-based models provides for greater realism than is available using distributed-development population models, which simulated mean rates with an empirically applied variability, or using ìbox-carî type models, which are excessively deterministic and do not allow for variability in growth or development rates of individuals having the same age.

The proposed model would simulate colony population dynamics as affected by worker force, labor needs, and food stores, as well as external conditions such as weather and food availability. Several colonies would be simulated, with the number of colonies for a physical area determined by resource availability and competition. Colony dynamics would be calculated for each colony, based on existing conditions within that colony, and based on environmental and food resource conditions.

The model would integrate general developmental biology (Tschinkel 1993), genetic structure including the basis for single vs. multiple queens (Keller & Ross 1995, Ross 1993, 1997, Ross & Keller 1995, Ross et al. 1996), colony forming behavior (Adams & Tschinkel 1995, Balas & Adams 1996, Bernasconi & Keller 1996, Tschinkel 1996), reproduction as a function of food availability (Goodisman & Ross 1996), queen regulation and reproduction behavior (Bhatkar 1990, Pesquero et al. 1993, Van der Meer et al. 1992, Vargo 1993, Vargo & Porter 1993, Vinson & Ellison 1996), foraging behavior and colony energetics (Bhatkar 1987b, 1988a, Hoope & Rust 1997, Macom & Porter 1995, 1996, Porter & Tschinkel 1987, Tschinkel 1988, Van der Meer et al. 1992), colony competition and nestmate recognition (Adams & Tschinkel 1995a, c, Balas & Adams 1996a, Bhatkar 1988b, Porter et al. 1991), resource sharing between colonies (Bhatkar et al. 1992, and as suggested by results from Drees et al. 1992), colony relocation behavior (Collins & Callcott 1995), biotic and abiotic mortality (Briano et al. 1995, Buschinger 1995, Fowler et al. 1995, Kleespies et al. 1997, Pesquero et al. 1995, Stimac et al. 1993), temperature activity thresholds (Killion & Grant 1995, Porter & Tschinkel 1993), winter hardiness (Diffie et al. 1997), and chemical, mechanical, and biological control efficacy (Catangui et al. 1996, Collins & Callcott 1995, Drees et al. 1992).

Incorporation of metabolic rates into the fire ant model is of particular importance in marginal climates, where either due to extreme temperatures or limited resource availability, colony reproduction and survival is tied to metabolic rates. The incorporation of metabolic rates would enable the proposed model to more accurately predict colony dynamics at the moving edge of invading populations, areas which often receive the most public attention.

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