Being able to identify how predation and competition influence natural selection is essential in understanding the evolutionary ecology of a population of species. In predation, substandard individuals are inherently selected. By substandard these are the young, sick and physically unfit individuals. As a result, preys also evolve into a more resilient ones putting pressure also to the predators. This scenario reflects a coevolution of both predators and preys. In this study, we will examine the predatory-prey relationship and understand the dynamics involved in relation to environmental changes.
Four different kinds of prey and five different kinds of predator were considered in this study. They preys were represented by four different species of beans which is polymorphic for color (i.e. white, red, black and speckled) and equal numbers of population size. Predators were classified as follows: groups hunting with their index finger and thumb, forceps, fork, spoon and knife. It has been assumed that the area can only support a given number of predators. The success of the hunters ultimately determines the relative number of each predator. The success of both predators and preys was observed up to the fourth generation. Trends of survival rate and the number of predators in four generations (expressed in percentage) were analyzed using Microsoft Excel.
Results revealed that two species of predators were driven to extinction in the successive generations. These two species were outcompeted by three predators (i.e. forceps, hand and spoon) (Figure 1). While the population size increases for both forceps (from 5 to 11 individuals) and spoon (from 5 to 6 individuals) in the second generation, the population size of hands remain at constant and in equilibrium. In the third generation, both species of forceps (33%) and spoon (11%) were outcompeted by hand (45.1%) in terms of the percentage of prey eaten.
Figure 1. Predation Rate of Selected Predators in Four Generations. The graph indicates the performance of each predator (i.e. forceps, hand, spoon, fork and knife) in hunting prey expressed in percentage. Zero percent of prey eaten indicates that there is no incidence of predation because the predator became extinct.
The population of hand doubled (i.e. from 4 to 8 individuals) while the population of forceps (from 11 to 9 individuals) and spoon (from 6 to 3 individuals) dropped. Only 2 forceps and 1 spoon remained while the population of hand decreased by 2 individuals leaving only a total of 6 individuals in the fourth generation. Predation performance of spoon lags at a point where its population has increase in the second and third generation as opposed to the trend seen in the species of forceps. In the case of hand, predation performance still increased (56.3%) while its population number decreased (Figure 1).
Figure 2 Survival Rate of Prey in Four Generations. The graph shows the performance of each prey (i.e. white beans, red beans, black beans and speckled beans) in escaping predation over time. The performance of prey is indicated by the percentage of survivors per generation.
The prey that has the highest survival rate is the species of red beans. Result revealed that species of red beans have a 52.4% survival rate which is more than twice the percentage of the black and speckled beans. The species of white beans have only 2% survival rate (Figure 2).
There appears to be a competition of resources among predators. The species of knife and fork were driven to extinction because of limiting resources such as food, space. As for spoons and forceps being outcompeted by hands, it is possible that intraspecific competition may have occurred among the same species. Both species of forceps and spoon may have also reached their carrying capacity which drives intraspecific competition. The hand population has increased in numbers by being able to adapt quickly to changes within its environment in the third generation. Coevoultion have been demonstrated in the case of hand and prey. Predation performance of the hand has significantly increased in the succeeding generations as well as the survival rate of prey in the fourth generation.
The morphological features of both fork and knife species affect their success rate in competing with other predators for resources. The sharp pointed features of a knife and fork cannot penetrate the dry and hard seed coat of kidney beans. Further, both fork and knife do not have the gripping mechanism that the hands and forceps have when securing their prey. While the spoon does not have an efficient gripping mechanism as compared to that of the forceps and the hand, it features a deep depression that could be used to scoop its preys. However the grip of the index finger and the thumb has the most advantage of all predators because it is easily adapted to different kinds of environmental conditions. The hands that control the forceps eventually become tired. Further, the forceps cannot be used to pick up heavy things.
Environmental stability favors the high survival rate of red beans. The advantage of red beans over other preys is that they grow and mature quickly over time. This prey may also have a longer range of dispersal pattern as opposed to other species of prey.
The coexistence of five predators in a particular area could be possible through resource partitioning—differences of use of resources among coexisting species. When a predator feeds preferentially, that is being able to discriminate among species they prey on—minimizes the cumulative density effect. In turn, this allows coexistence among many species. This is because diet shifts in predators in response to changes in time and space in resource availability allow rare species of prey to be completely eliminated. Excessive predation is also being avoided when preys put pressure to the predators end as their population count decreases.
In summary, predation and competition are two main concepts that are key to understanding biodiversity and evolution of species. The interplay that exists between a predator and prey has been well demonstrated in this study. Species that were outcompeted and were driven to extinction is a result of limiting factors such as resource availability, competition for foraging area and the like. Morphological features of predator species can be also among the many factors that determine the success of the species to reproduce and proliferate in succeeding generations. Coevolution has also been well demonstrated in this study as shown in the increasing survival rate and predation rate of the prey and hand respectively. The differences in survival rates of preys demonstrate how preys respond to predatory pressures and evolve to become more resilient over time. Environmental stability promotes the resilience of red beans for instance against predation. Likewise, predators also develop their foraging skills over time. The predation performance of the species of hand has been found to significantly increase throughout succeeding generation. Coexistence may be possible through resource partitioning and diet shifts among predators thereby promoting species richness. Again, excessive predation is also being avoided when preys put pressure to the predators end as their population count decreases.