How many animals does an ecosystem need? The results may surprise you.

How many animals does an ecosystem need? There is an article on the Australian Academy of Science blog titled ‘What would happen if a fish went extinct on the Great Barrier Reef?‘ about the role of animals in the functioning of coral reef ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More. Thank you @ProfTerryHughes for sharing on Twitter.

In ecosystems, each animal plays a role and their functions are partitioned. This seems rather obvious. When you consider that if all animals had exactly the same function(Of an ecosystem). A subset of ecosystem processes and structures, where the ecosystem does something that provides an ecosystem service of value to people. More, there could be no ‘ecosystem’. That would be like running a farmers’ market with farmers but no delivery personnel, no people to put up the market stalls, no stall-holders or customers. Like economies, ecosystems cannot exist without functional animal diversity.

Remember, all ecosystems (and economies) are animal-driven, because wildlife is the mechanism that builds them. The existence of animals and the environment is part and parcel. This is because it’s animals that stabilise the free surplus energy that primary producers make. Otherwise the system crumbles and animals can’t exist.

It’s a fundamental law of nature that animals exist because they are the most likely lifeforms to minimise environmental chaos. If we remove animals, the ‘eco’ part (which in ancient Greek was oikos and meant the combination of family, household and property) is lost. Any such system collapses.

Results of the study on animals and ecosystems

The Australian Academy of Science blog refers to a study done in 2014 [1] that looked at how many coral reef fish perform certain critical functions. The researchers looked at coral reefs from the western Indian Ocean to the eastern Atlantic. These are habitat for a total of 6,316 fish species.

The scientists categorised the fish based on their characteristics. For example, size, mobility and diet. This resulted in 646 different groupings e.g. one group was fish that are large, pelagic, planktonA soup of micro-organisms. Usually refers to all the zooplankton and algae in the ocean but can also be used to describe tiny insects in the atmosphere (see aerial plankton). More feeders; another small, nocturnal, grazers and so on. Each of these groups relate to a particular niche, which is another way of saying, how an animal makes a living.

The study revealed that for nearly 40% of these categories, only one fish species was connected to related ecosystem services.

The ecosystem role of fish on coral reefs

Go back to the market analogy. How many grocers are there? How many book sellers? How many people are employed to erect the stalls and take them down each day? How many van drivers … for specific products? How many market managers, admin staff and so on. The list of ‘animals’ needed to minimise disorder(Of energy and ecosystems). Ecosystems are thermodynamically driven. Disorder occurs when energy dissipates and becomes more chaotic. For example, the release of hot air into the atmosphere results in that energy is freer to disperse (maximum entropy). The opposite is true when energy is locked into biological processes, when it is stored inside molecules (minimum entropy). Stability in ecosystems occurs More in something as simple as a weekly market is surprisingly large but still, the number of people responsible for specific roles is one or two at the most.

The results of the coral reef study, therefore, should come as little surprise – the fact it may, could reveal how little most of us understand about how ecosystems work or our own animality, since we construct economies on the same principles and wouldn’t for a moment imagine that sacking van drivers that bring food to a farmers’ market would be a sustainable option.

Another outcome of the study is an indication of the scale and intensity of the impact animals have on ecosystems.

What makes the study all the more remarkable is that systems like coral reefs have practically infinite complexity, yet this shows they can be maintained in working order by only a few thousand species … based on the partitioned roles and action of a few individuals, across most of the planet’s coral reef ecosystems.

We should not forget that animals living in healthy ecosystems contribute to their stability, despite having such massive impact. Wildlife doesn’t ‘feed on’ habitat, it has an integral role in the creation and preservation of its environment. It has to be that way, or else the ensuing ecosystem chaos and collapse, would cause any species to go extinct.

This is nicely illustrated via the case of the Bumphead Parrotfish.

The remarkable Bumphead Parrotfish

There may be 3.9 million Bumphead Parrotfish fish in the world [2] and each animal consumes about five tonnes of coral a year [3]. With sand weighing about 1.6 tonnes per cubic metre, this means the population as a whole is processing 122 million cubic per annum. If people were to consume an average box of cereal every two weeks, it would take the population of Australia 577 years to consume an equivalent weight in cereal.

The Port Phillip Bay Channel Deepening Project in Melbourne, Australia, was a three-year program to deepen channels for larger ships and dredged 22.9 million cubic metres of material, creating an imprecisely-understood level of permanent and irreversible ecological impact. In the same three years, Bumphead Parrotfish would have created 366 million cubic metres of coral reef erosion, contributing to the healthy functioning of an environment and cost us nothing.

The importance of animals for ecosystem stability

There is nothing man-made that is anywhere near as exquisitely constructed as an ecosystem that animals build, or provides as much equity for survival. Nothing we engineer is able to reduce environmental disorder, maximise efficiency or provide as many jobs, as elegantly as a coral reef.

Furthermore, the only way to reengineer ecosystems is to set the same animals to the task as created them in the first place. There is no other solution. There is no way a single species – human – alone, can recreate this complexity without crushing a system’s stability while we do it. There simply aren’t enough of us … in the case of coral reefs, we can’t breathe underwater and we don’t have the functional ecology to be able to eat eat coral, cultivate-graze algae or defecate sand like a Bumphead Parrotfish.

This should give us all pause for thought, because these rules don’t just apply to coral reefs. Every ecosystem works in a similar same way and we will depend on all other animals to help minimise environmental disorder if we are to have a future on Earth.

Spotlight

From Australian Academy of Science blog titled ‘What would happen if a fish went extinct on the Great Barrier Reef? Graph showing the functional diversity of fish communities in the Indo-Pacific region, which includes the Great Barrier Reef.

Scientists on Ningaloo Reef have just calculated that the amount of coral consumed by a Bumphead Parrotfish in a year could even be as high as 13.42 tonnes/ha.

References

1. Mouillot, David & Villéger, Sébastien & Parravicini, Valeriano & Kulbicki, Michel & Arias, Ernesto & Bender, Mariana & Chabanet, Pascale & Floeter, S. & Friedlander, Alan & Vigliola, Laurent & Bellwood, David. (2014). Functional over-redundancy and high functional vulnerability in global fish faunas on tropical reefs. Proceedings of the National Academy of Sciences of the United States of America. 111. 10.1073/pnas.1317625111.
2. Kobayashi, D.R., et al., Bumphead parrotfish (Bolbometopon muricatum) status review. 2011.
3. Bellwood, D., A. Hoey, and J. Choat, Limited functional redundancy in high diversity systems: ResilienceReferring to an ecosystem’s ability to maintain a steady stable-state. The need to build resilience is entirely anthropocentric and symptomatic of ecosystems that are damaged or declining, leading to loss of ecosystem services on which humans depend. More and ecosystem function on coral reefs. Ecology Letters, 2003. 6: p. 281-285.