Ecological interactions: Predation

Predation is when an organism kills and eats another organism (prey) to gain energy necessary for reproduction. In the perspective of the prey, predation reduces fitness. Predation is therefore a type of antagonistic interaction, a biotic factor limiting species distribution [1][2]. However, predation is also important to promote biodiversity through adaptation[3].

Types of predation

1. Carnivory - a type of predation where one animal consumes another. Carnivory is obviously displayed by large animals. Examples of these are wolves hunting moose, eagles hunting monkeys, cats hunting mouse, etc. Another form of carnivory is group predation. This is usually observed in ants and spiders as well as social carnivores such as lions and hyenas[1]  where a group of individuals of  the same species are feeding on one large organism .

Plants can also become carnivorous predators. Although they are not mobile, they are still able to capture animals. Examples of this is the Venus fly trap and the pitcher plants. Both plants use chemicals (digestive enzymes) to absorb the nutrients from the insects they trap[1].

Bacteria and protozoa also engage in carnivorous predation. Population and size of microbial communities are maintained by such interaction. This promotes the diversity of microorganisms and therefore contributing to a stable community structure[1].

2. Herbivory - a type of predation where an organism consumes plants or algae to obtain energy. Most common example of herbivory is grazing of cattle. Seed consumption is an example of such predation. Seeds can be considered an organism, and when seeds are consumed, it is already killed before growing into a mature plant[1]. 

3. Parasitism - a type of predation in which organisms derive their energy from the host by slowly consuming it and in most cases killing it in the process[3]. 

There are two types of parasites; the endoparasites and the ectoparasites. Endoparasites live inside the body of the host. Examples of these are flukes, tapeworms, fungi, etc. Ectoparasites live outside the body of their host. Examples of these are ticks, mites, and lice[1].

By definition, parasites do not kill their hosts, but in some instances, they can cause diseases. In such situation, they are referred to as pathogens. Pathogens decrease fitness of their host by causing disease, eventually killing them. There are also instances where a host is used by a parasite as medium to lay their eggs. This can cause death to the host as hatched larvae will consume the host from the inside, slowly killing it. This type of parasite is referred to as a parasitoid[1].

Predation contributes to biodiversity and a stable ecosystem

Predation causes pressure on species to adapt to be able to survive. Organisms adapt by developing characters necessary to their roles as either prey or predator. This is referred to as Co-evolution. This results to diversity among species within the community[3]. 

Adaptation by preys:

Preys are constantly on the lookout to avoid predators. To effectively do this, organisms have developed characters to avoid detection, capture , and handling[3].

1. Avoiding detection. Cryptic coloration or camouflage helps preys to blend to the background. The ability to camouflage allows them to avoid being targeted by predators. Such characteristic is displayed by tiger beetles, stick insects, and leaf insects, to name a few.

2. Avoiding capture. Capture by the predator can be avoided if the prey is able to escape. This is displayed by animals with the ability to run fast like for example, the antelopes. However, some animals are too slow to avoid capture. Such animals use a different technique. Bisons, for example, cannot outrun their predator (i.e. wolves). To ensure survival of their species, they forage in groups. Although not all bisons are able to avoid capture when predators  attack, specific individuals will not be targeted specifically, especially the fit members of the group[3].

3. Avoiding handling. Since plants are not mobile, they have to develop characteristics for them to avoid predation. Plants have evolved defenses such as thorns and chemicals like nicotine and tannins and use them to fend off their predators, reducing damage done by herbivores[1][3].

Animals also evolved characters to avoid handling by predators. They display color patterns to imply that they are poisonous and unpalatable.

• Aposematic coloration (also known as warning color) is the coloration in prey organisms that warns the predators of their unprofitability, suggesting that they are poisonous [3][4]. Preys with aposematic coloration are usually conspicuous (with bright colors) and luminous. This ensures that predators are automatically reminded that such preys are to be avoided. The luminance of such colors also facilitates predator aversion learning[4]. Organisms with aposematic coloration are coral snakes (displaying red and yellow bands)[3] and Chinese mantids[4].

• Mullerian mimicry is a resemblance of color pattern between two unpalatable organisms such as bees and wasps[3][5]. Such mimicry aids in predator avoidance because the predator has learned to avoid organisms with similar color pattern[5].

• Batesian mimicry is when a harmless organism imitates the coloration of an unpalatable organism. The mimic gains protection because the predator mistakes it as the unpalatable organism[6]. 

Adaptation by predators

Survival of a predator is dependent on it's ability to successfully catch prey. Therefore, it also needs to evolve characters to improve efficiency in catching prey.

Examples of adaptive evolution by predators is the heightened sense of smell and sharp teeth of wolves, the sharp eyesight of eagles and it's strong talons to effectively grip preys[3]. Non-carnivorous animals also evolve characters to avoid unpalatable prey. Butterflies, for example,  have chemical sensors on their feet to allow them to taste the plant before consuming any part of it[1].

Predation plays an important role to maintain a stable ecosystem . Predation regulates population size by preventing the prey population becoming overly abundant[1]. Predators can affect diversity positively by preying on competitive dominant species or by reducing consumption of foundation species[7]. This creates a balanced ecosystem. Carnivory, herbivory, and parasitism  can change the balance of the food web. Removal of any of the three interactions can have a negative impact on the ecological community[1].

References

[1]Stevens A. 2010. Predation, herbivory, amd parasitism. Nature Education Knwledge. 3(10):36

[2]Reece, J. B., Urry, L. A., Cain, M. L. 1., Wasserman, S. A., Minorsky, P. V., & Jackson, R. (2011). Campbell biology (Ninth edition.) Pearson Benjamin Cummings
[3]https://www.youtube.com/watch?v=mFDiiSqGB7M
[4]Prudic KL, Skemp AK, and Ppaj DR. 2007. Aposematic coloration, luminance contrast, and the benefits of conspiciousness. Behavioral Ecology. Vol.18, Issue 1; 41-46.
[5]https://www.britannica.com/science/Mullerian-mimicry
[6]https://www.britannica.com/science/Batesian-mimicry
[7]Smee DL. 2010) Species with large impact on community structure. Nature Educatio Knowledge. Vol. 3(10);40.