Tim Payer, Cohort Based Intraspecific Competition for Refuge Space and It’s Effect on Predator-Prey Persistence: A Simulation Model.

Abstract: A population simulation model was built to study the effect of cohort based intraspecific competition for refuge space upon the persistence of a predator-prey system. The distribution of refuge space allotted to four cohorts of prey was varied in three scenarios to simulate competition that favored a particular cohort size. The three scenarios are of increasing, equivalent, and decreasing allocations of refuge space to cohorts with increasing size. The generation of offspring for both predator and prey is biomass based. The decreasing allocation scenario was found to be the most stable, as it maintained system persistence with a refuge space 3% smaller than that required for the other scenarios. The greater stability of the decreasing allocation scenario is due to its greater share of immature prey protected within refuge space. Immature prey directs a larger share of its energy towards growth rather than reproduction. The competition for refuge space expels a larger quantity of faster growing but less prolific immature prey to open space for predation. This supports a larger predator population to regulate a less prolific prey, discouraging explosive prey growth and enhancing the stability of the system.

Garrett C. Gregor, Modeling the Juvenile Bottleneck on Largemouth Bass (Micropterus salmoides) Caused by Threadfin Shad (Dorosoma petenense).

Abstract: A mathematical model was developed to study the juvenile bottleneck between largemouth bass (Micropterus salmoides) and threadfin shad (Dorosoma petenense). Results for two investigations are examined through employing computer simulations of the mathematical model. In the first investigation, population equilibria were analyzed for varying strengths of three biological parameters; bass growth, shad competition, and bass predation. The population of large adult bass were most vulnerable to shad competition. For large adult bass to be successful, bass growth had to be strong if shad competition was strong. The level of bass predation had little effect against shad competition. The second investigation employed a hypothetical management strategy where a percentage of shad was removed every year. Shad removal had a positive effect on the density of large adult bass when shad competition and bass growth were strong and a negative effect on the density of large adult bass when shad competition was weak.

Neil B. McConlogue, Optimizing Habitat Preference Using Natural Selection: A Spatially Explicit Simulator.

Abstract: A model is presented that simulates selection for habitat preference on a heterogeneous landscape. Automata are generated that carry a binary code representing their preference for the higher quality of two possible habitats. Higher preference means greater probability of finding a high quality site, but also a higher risk of not finding a breeding site at all. The automata mate and pass this "genetic" information to their offspring. Successful automata produce more offspring, and pass more preference and/or non-preference alleles to the next generation. The population’s mean proportion of preference alleles rises or falls in response to the degree that habitat preference is favored. Simulations compared selection for habitat preference, while varying landscape fragmentation, search rat, and differential birth rate between source and sink habitats.

Factors that increased selection for habitat preference were higher reproductive differential between the two habitats, and higher habitat fragmentation. Increasing the search rate did not, as might be expected, lead to higher habitat preference. These results disagree with a similar study done by Ward (1987). Unlike Ward’s model, the model presented here allows dynamic occupancy rates. High search rates had a secondary effect of increasing the occupancy of breeding sites. High occupancy rates, in turn, had the effect of raising rather than lowering the risk to searchers.