The Ecology of Undesirable Organisms

By Jasmine Gunton

An integral part of human nature is to place every object in the universe into a hierarchical ranking system. We can see these hierarchies in social constructs such as class distinctions, businesses, and political systems. Additionally, hierarchies have an established role in science, with many biologists over human history attempting to place the Earth’s many living organisms into a structured grouping. The most common of these ranking systems today is the Linnaean taxonomy. In this system, different species are grouped into a kingdom, phylum, clan, and so on [1]. However, other systems are still insidiously ingrained into the human understanding of biological theory, with one of the prime examples being the ‘tree of life’. The tree of life places humans at the top of the proverbial tree, supposedly being the most intelligent and sophisticated animal. ‘Inferior’ species such as apes and reptiles are placed at lower branches. Finally, the prokaryotes are placed at the base of the trunk, being deemed as the most simple and unintelligent creatures [2].

The discipline of ecology challenges this old view, instead opting to view organisms in the context of the highly complex ecosystems in which they occupy. Ecology recognises that each species within an ecosystem contributes greatly to the functioning of that ecosystem through indirect and direct interactions with other organisms and their environment.

Nevertheless, some organisms are still viewed by the public as ecologically useless and undeserving of conservation efforts. I would like to explore why such creatures are, in fact, biologically important, and why their identity in popular culture should be reconsidered.

Rattus

Rats are one of the first creatures to come to mind as being universally disliked. This reputation has been sculpted by the rodents’ tendency to spread deadly pathogens and parasites to humans [3]. But you already know why rats are considered repugnant. Instead, let us look at why this rodent is beneficial to its native environments. Along with various pathogens, rats are also transporters of mass quantities of plant seeds. For example, in southwest China, Edward’s long-tailed rat (Leopoldamys edwardsi) is the main dispersal vector of the seeds of the tea oil camellia (Camellia oleifera). It just so happens that the long-tailed rat is also a voracious consumer of these seeds. In true rodent fashion, the long-tailed rat will hoard the seeds it has collected in various subsurface burrows. This effectively disperses the tea oil seeds, increasing the population’s chance of survival. The survival of tea oil camellia is therefore directly dependent on the abundance of long-tailed rats within the region [4]. Another important rat species is the Californian giant kangaroo rat (Dipodomys ingens). In the sandy grasslands of California, the kangaroo rat acts as a keystone species and habitat engineer of the ecosystem. Services provided by the kangaroo rat include soil disturbance and the creation of vast burrow networks that act as a habitat for other native species. By changing habitat structure, the kangaroo rat alters the community composition of the ecosystem, exerting positive effects on plant and invertebrate diversity, as well as lizard and squirrel abundance [5]. The vital presence of rats in these community structures conveys their ecological importance. It is important to note that in these situations, rats are native to the community, unlike in New Zealand where they are considered a threat to native ecosystem structures.

Fungi

It is not only animal species that receive negative attention from the human population. Mould, as many websites would tell you, is undesirable to have in the home as it releases mycotoxins that can be harmful to humans [6]. While not particularly useful within a house, mould has many benefits for its native ecosystem. Now, just to make things clear before explaining its ecology, mould is neither an animal nor a plant. It is instead part of the eukaryotic group of organisms known as fungi. This means that mould and other fungi species are special, and not like the other organisms. The taxa ‘mould’ has been given to multiple polyphyletic groups of fungi, so for the sake of simplicity, we will treat both fungi and mould as if they are the same. Native to every continent, fungi are incredibly hardy and ancient, having evolved symbiotic relationships with several plant and animal species [7-9]. One of the most important roles that fungi play is the decomposition of organic material. In almost every ecosystem, the same cycle of decomposition takes place.

When organisms die, their bodily material is digested by various species of fungi. This digestion process converts the organic material into nutrients that plants can use. Herbivorous animals eat these plants, the animals eventually die, and the cycle is renewed. Fungi can also benefit plants through a mutualistic relationship known as mycorrhizae. Mycorrhiza is a symbiotic association between a fungus and the roots (or the rhizosphere) of a plant. The plant supplies sugars from photosynthesis to the fungi, and the fungi in return supply the plant with water and nutrients such as phosphorus and nitrogen, which are taken from the soil [10]. For some plant species, mycorrhizae are essential for the effective establishment and growth of the plant. Therefore, the survival of certain plants in an ecosystem depends on the existence of, and services provided, by fungi [11].

Vespidae

Ample information has been included in this article concerning the benefits provided by foragers and decomposers. Now I want to discuss the question, how do predators benefit their respective ecosystems? One cannot deny that wasps are menacing, aggressive, and persistent in their violence. Yet, these qualities are what make wasps such beneficial predators in their ecosystem. Once again, this discussion of the benefit of wasps to their environment is focusing on their native environments. Wasps prey on a number of insects, including caterpillars, cicadas, flies, and beetles. By feeding on these carnivorous and herbivorous insects, the wasp indirectly protects both insects and plants in the lower levels of the food chain [12]. However, wasps are only predators of insects in a certain sense. Adult wasps do not actually eat insects, preferring instead to paralyse their prey and feed it to their larvae [13]. Nevertheless, this process ensures that certain insect species do not become over-abundant in the ecosystem. As well as performing natural regulatory services, wasps have substantial potential to act as biological pest control agents in urban and pastoral regions. A study by Prezoto et al. suggests that wasp colony management is a cost-effective and feasible technique in controlling pest species [14]. It is not only their violent nature that makes wasps an asset to their ecosystem. In addition to predation, wasps also act as pollinators for a large range of plant species (which is a fact I'm sure bee enthusiasts greatly detest). In fact, Brock et al. found that 164 plant species were solely dependent on aculeate wasps for pollination [12]. Perhaps we should display the same amount of appreciation for wasps as we do for another certain flying insect.

Columbidae

The last example I wish to discuss has been described by some as a ‘flying rat’. This species often inhabits cities and feeds on food scraps discarded by humans [15]. I am talking about none other than the pigeon. Despite once being used by humans for communication, pigeons have sadly earned a reputation less than favourable [16]. It is thus my duty to convince you, the reader, of the pigeon’s usefulness in its ecosystem, and to inform you of its charismatic qualities. Similar to the long-tailed rat, pigeons are important distributors of plant seeds. Pigeons are especially effective at seed dispersal as they travel long distances away from the parent plants. For example, the New Zealand Kererū (Hemiphaga novaeseelandiae), or ‘wood pigeon’ is an important seed disperser of the native tree species Beilschmiedia tawa (Tawa), Vitex lucens (Pūriri) and Pseudopanax arboreus (Five-finger) [17]. In other countries, pigeons are an important food source for many species of falcons, including the peregrine falcon (Falco peregrinus) [18]. The peregrine falcon itself is also important in its ecosystem as a predator of several other bird species, including ptarmigan and ducks. Therefore, by supporting peregrine falcon populations, the pigeon indirectly helps to regulate other bird species [19]. Another interesting fact (that admittedly does not have much to do with its ecology) is that pigeons have excellent visual discrimination skills. A study by Watanabe et al. showed that pigeons can be taught to discriminate between the artworks of Claude Monet and Pablo Picasso [20]. In a later paper, Watanabe displayed that it was possible to teach pigeons how to discriminate between the paintings of other artists, including Van Gogh and Marc Chagall [21]. The pigeon’s discrimination skills do not stop at only paintings. Pigeons are also able to discriminate between human individuals and have shown a basic understanding of human behaviour [15]. I hope that I have persuaded you not only of the pigeon’s ecological importance but also of their intellect and charm.

Concluding Statements

In this article, I have described the ecological importance of only a few species, placing emphasis on those considered undesirable by many people. In truth, all organisms are ecologically important to the functioning of their native habitats. Biologists often use the terms ‘keystone species’ and ‘species engineer’ to denote species that appear to be more vital than other species to their respective environments. In my opinion, hierarchical categorisation is impractical in both ecology and the wider field of biology. In research and the application of environmental management, scientists need to stop thinking of organisms as being in an ecological ranking, but rather as part of the highly complex system of abiotic and biotic elements that make up an ecosystem. Nature does not view one animal as inherently ‘better’ than another, and neither should we.

References

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2. E. Haeckel, The Evolution of Man: A Popular Exposition of the Principal Points of Human Ontogeny and Phylogeny, 1st ed. New York, NY, USA: D. Appleton & Company, 1879.

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