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Loss of Apex Predators Can Devastate Ecosystems: Implications for the Hedonistic Imperative July 30, 2011

Posted by Metabiological in Ecology, Transhumanism.
Tags: , , , ,

One of the big debates in the field of ecology is whether or not ecosystems are regulated by bottom-up or top-down processes.  Bottom-up refers to elements at the bottom of the food chain that control the structure of the biotic community; such as the amount of nutrients in the environment determining the composition of the primary producers which in turn determine the composition of the herbivores and predators.  Top-down control is just the opposite, in which the organisms at the top of the food chain (i.e. the apex predators) control the structure of the rest of the ecosystem through the pressure they exert through predation.

The debate has been raging for decades now and it is now widely acknowledged that both types of regulation occur in nature.  As such debate has largely shifted to the question of which form predominates and under what circumstances either form will.  Personally, and I emphasize this is a personal opinion, I tend to think that bottom up processes largely control the structure of ecosystems (annual rise and fall of nutrient levels in marine systems, sunlight in almost all systems) with top down processes only becoming apparent in areas where bottom up limitations are largely negligible (areas where nutrients are abundant all year round).

Still decades of research have shown that in many systems the presence of an apex predator can have a drastic effect on the ecosystem in question.  In a recent study led by James Estes, who knows a thing or two about apex predators, a worldwide assessment of human induced trophic cascades attempts to bring the problem into focus.

According to first author James Estes, a professor of ecology and evolutionary biology at the University of California, Santa Cruz, large animals were once ubiquitous across the globe, and they shaped the structure and dynamics of ecosystems. Their decline, largely caused by humans through hunting and habitat fragmentation, has had far-reaching and often surprising consequences, including changes in vegetation, wildfire frequency, infectious diseases, invasive species, water quality, and nutrient cycles.

The decline of apex consumers has been most pronounced among the big predators, such as wolves and lions on land, whales and sharks in the oceans, and large fish in freshwater ecosystems. But there have also been dramatic declines in populations of many large herbivores, such as elephants and bison. The loss of apex consumers from an ecosystem triggers an ecological phenomenon known as a “trophic cascade,” a chain of effects moving down through lower levels of the food chain.

Though this is interesting in it’s own right what really got me thinking is what implications this has for the Hedonistic Imperative.  I’m going to assume that anyone reading this has at least a basic working knowledge of what the Hedonistic Imperative is (if not, see the link to the right) and if you do then you probably already know where I’m going with this.  Apex predators will not, and cannot, exist in a world free from suffering.

What would this mean then?  Would a world without predators be a barren and lifeless one, or completely chaotic with ecosystems rising and falling like the tides?  Well, not necessarily.  A lot of the talk surrounding the discussion of apex predators gets bogged down in emotionally charged language that does little more than distort the issue.  It doesn’t help that apex species are almost exclusively “charismatic megafauna” (as one of my professors delights in calling them) and tend to attract attention and importance in the human psyche sometimes out of proportion with their actual role in the ecosystem.   But to get back to the emotionally charged language part all you need to do is look at some of the words used when describing the consequences of removing apex species.  Devastate.  Destroy.  Collapse.

Those are some pretty heavy words, but are they accurate?  Yes and no.  There’s no doubt that the loss of an apex species can drastically change the structure of an ecosystem and for many species the changes are negative.  However, that is not always the case.  Take arguably the most common example of a trophic cascade; the loss of sea otters in the eastern Pacific and the growth of “urchin barrens.”  In short, sea otters were hunted near to extinction and the loss of this species lead to a massive growth in sea urchin populations, of which the sea otter was a primary predator.  This explosive growth lead to a reduction in the size of kelp forests as urchins devoured everything in their path.  The result was areas stripped clean of kelp and colloquially known as urchin barrens.

This is a fairly well known story and one with a fair amount of evidence behind it, though the truth is a bit more complicated.  Whether or not an explosion of the urchin population results in a true, sustained barren seems to depend on a variety of local factors including temperature, seasonal changes in food quality and the presence of other predators.  In short, simply removing the top predators does not necessarily result in ecosystem collapse.

That right there is the point I’ve spent the last seven paragraphs or so laboriously trying to get to.  There are other ways to regulate ecosystems besides requiring predators to occasionally thin out the herbivore populations.  This, as stated above, has important implications for the Hedonistic Imperative as it provides us with the possibility of designing self-sustaining ecosystems without the need to release what are essentially serial killers into them.

The use of the word self-sustaining there is important.  An important critique of HI is that redesigning the world’s ecosystems will require a massive, centralized decision making and control body and constant monitoring and intervention to stay one step ahead of evolution.  Unfortunately this is likely to be true to a large degree.  As such it is important to look for any opportunity to take the burden off of ourselves so to speak and arrange for cruelty-free ecosystems to sustain themselves through natural processes.

How can we do that?  Well here it gets a little murky since any real solution is probably centuries away from us at our current level of development.  Still, even with our woefully inadequate understanding of how ecosystems function we can at least put forth a couple of ideas.

One way to control population sizes without the need for predators is to control population birth rates.  Obviously we won’t be able to go around and hand out condoms to the animals so organisms will have to be engineered in such a way as to ensure low growth rates and stable populations sizes.  An evolutionary solution (i.e. engineer individuals to produce low amount of sex cells or breed only occasionally) will likely be unsustainable in the long-term since mutants which overcome those limitations will likely be able to out compete their slow growing neighbors.  A better solution might be designing animals to be dependent on something within their environment that keeps their birth rates low.  Fruiting plants might be designed so that their fruit contains chemical compounds which inhibit sperm or egg production.  This isn’t as far-fetched as it sounds and has tentatively been demonstrated in certain interactions between sea urchins and algae.  Even this would be vulnerable to evolutionary mutations so vigilance would still be required.

A similar method could be used with virus’ or bacteria that target an organisms reproductive system in the way described above.  Diseases actually would make a very effective means of population control due to the density-dependent nature of their effectiveness.  If the population drops below a certain threshold  the disease ceases to be as effective, due to the increased difficulty of finding a host, and the population is given a window to recover.  This advantage applies to all density-dependent checks on population growth (competition for mates and resources, predation, space limitation) but most of the rest would be very difficult to alter to ensure no suffering.  Diseases would also have the advantage of evolving with their victims to stay one step ahead them.  Of course by extension diseases present the obvious problem of mutating to attack organisms in some other way, one which may involve suffering and death.

Of course their are more fanciful, or perhaps I should say sci-fi, options as well.  Perhaps we could engineer a primitive, for lack of a better word, neural network a la Avatar that allows some sort of rudimentary communication between organisms, allowing the balance between food supply and population to be maintained.   That may be a little too speculative even for this article so I’ll leave it their for now.  The point is that a loss of predators from an ecosystem need not mean disaster and need not be an obstacle to the Hedonistic Imperative.  We can find ways around it using processes already present in the natural world.



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