What is a keystone species? Animals stabilise ecosystems, not drive them

What is a keystone species? The term was coined by American zoologist Robert Paine in 1969 as meaning an animal that has disproportionate effect on its surroundings. Conservationists will often use the keystone species argument to say that a particular species is worthy of protection, as without, the ecosystem will collapse.

Reintroduction of European Beavers in Scotland, for example, is considered to have had overwhelmingly positive influence on biodiversityWhat is the definition of biodiversity? When we ask, what is the definition of biodiversity? It depends on what we want to do with it. The term is widely and commonly misused, leading to significant misinterpretation of the importance of how animals function on Earth and why they matter a great deal, to human survival. Here I will try to More leading to healthier, more structurally complex woodlands. The killing of Alaska’s Sea Otters in North America for the fur trade, impacted fisheries, birds and coastlines. By the 1970s, the near-extinct populations had recovered and by chance, researchers noticed that where they lived, there were healthy kelp forests, even though the otters don’t eat kelp.

Do keystone species really exist?

There is no evidence of the singular importance of any species on 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. Absent megafaunaThe largest animals that represent the top of the trophic pyramid. These are the final building blocks in ecosystem structures for maximum entropy production. Megafauna can be measured at any spatial scale. The largest animal that ever lived on Earth is the Blue Whale. In a grassland, spiders could be considered megafauna The term is generally reserved for animals larger More will undoubtedly cause rapid change in the state of the environment but one species alone cannot stabilise a whole ecosystem.

Ecosystems are complex hierarchies of animals that moderate energyEnergy and nutrients are the same thing. Plants capture energy from the Sun and store it in chemicals, via the process of photosynthesis. The excess greenery and waste that plants create, contain chemicals that animals can eat, in order to build their own bodies and reproduce. When a chemical is used this way, we call it a nutrient. As we More by capturing waste from plants and entraining this into nutrientA substance that contains the raw materials for life. At a chemical level, these are contained inside compounds that are absorbed into the body and essential energy-containing molecules are extracted, so that energy can be transformed into other chemical processes that use the energy for living. More cycles. Ecosystems operate on the principle of thermodynamicsThermodynamics are at the heart of our understanding of ecosystems and not an altogether difficult concept to grasp but one that isn't widely taught to ecologists. Basically, all life on Earth, is derived from the Sun's heat. This renewable energy source constantly bombards ecosystems with energy but they would overheat, if it wasn't for the absorptive capacity of food webs. More and only stabilise when animal abundance is in certain proportions. For example, if you measure the abundance of animals in any pristine lake, pond, grassland or forest, or at scales of a garden pond right up to the Amazon rainforest, you’ll get roughly the same result.

The log(biomassThe weight of living organisms. Biomass can be measured in relation to the amount of carbon, the dry weight (with all moisture removed) or living weight. In general it can be used to describe the volume of energy that is contained inside systems, as the size of animals relates to their metabolism and therefore, how much energy they contain and More) of animals plotted against log(abundance) would be a straight line. Another way of representing this is as a trophic pyramidThe gradual reduction in energy content, increase in body size and reduction in number of animals, that occurs the higher you go up the food chain. At the base of the pyramid are a vast number of high-metabolism, tiny creatures and at the summit, are the top predators. To be stable, the pyramid has to have creatures at all levels. More e.g. abundant small insects near the basis and less abundant large mammal predators at the top. It’s the only shape where all free surplus energyThe energy of a system that is emitted as waste and is not part of ecosystem processes. There is always some free surplus energy as this creates the basis for evolution where new species exploit gaps in the ecosystem where free energy becomes available. Surplus energy can occur as a result of disruption or disturbance. When free surplus energy reaches More is more or less consumed (more specifically, you approach maximum entropy productionWhere an ecosystem achieves a steady stable-state with the maximum possible number of species and there is very little free surplus energy because it is all consumed inside biological processes. Entropy dictates that all matter moves towards chaos but animal life enables ecosystems to continually move in the opposite direction. Reaching a state of maximum entropy production is essential for More).

It’s the shape of this structure and its composition that makes it stable, not the existence of any one species. A disproportionately abundant species (or group of species) can just as well destabilise things. When it comes to single species loss, correlation is not necessarily causation.

The stability principle

While there is almost certainly some truth in the keystone concept for specific locations or situations, the trend is not scaleable. Clearly introducing sea otters or beavers everywhere, would not miraculously fix all the world’s ecosystem problems.

Especially in a world where we have massively reduced wildlife populations already, we have to take great care not to assume, that any one species is the key to fixing ecological problems. In fact what we should be doing, is looking at the shape of these systems and trying to restore those structures. Everywhere we go, we should be looking for what’s obviously missing and try to remedy that as a priority.

In this way, species never “drive” ecosystem change, it’s the community of animals that, in the right proportions, “stabilise” ecosystems. It’s an important distinction to make, if we’re to secure the longevity of conservationWhy is animal conservation important? Animal conservation is important, because animals are the only mechanism to create biodiversity, which is the mechanism that creates a habitable planet for humans. Without animals, the energy from today’s plants (algae, trees, flowers etc) will eventually reach the atmosphere and ocean, much of it as carbon. The quantity of this plant-based waste is so More outcomes and avoid making costly and arbitrary decisions. This is why I am not a great fan of those who say we should prioritise saving only certain species. Who makes that decision and why would sacrificing one species for another, be a robust survival strategy? I doubt most conservationists have thought this through.

Why do we need stable ecosystems?

And you may well ask, why do we need stable ecosystems at all? Well, instability is a greater threat to our own economic viability than presence / absence of food.

Farms that can’t predict their profitability over a reasonable time-scale, or fisheries that regularly fail to reach profitable quotas, are of little use. If we know there is no food to harvest, then we wouldn’t waste our time.

Ecosystem instability, caused by loss of biodiversity and concurrent collapse in the biodiversity-coupled climate system, is causing billions of dollars through uncertainty. Let’s face it, if your local baker couldn’t guarantee a supply of bread each morning, you’d probably choose another place to shop. We don’t have that luxury when it comes to global food security.