Excluding the Competitive Exclusion Principle: Why the World is Not a Zoo

As an undergraduate, I worked several summers in a microbiology lab, as a technician. I made and poured culture media. I learned to streak agar Petri dishes in a way which would allow isolation of multiple organisms. One problem, when culturing gram negative organisms, is the way that a motile species, such as the Proteus mirabilis species shown above, may rapidly overrun other colonies, making isolation for identification of other organisms more difficult.

In biology, the competitive exclusion principle is a theory of ecology which states that two species with identical resource requirements cannot coexist. This theory, as developed using micro-organisms in cultures by Georgy Gause around 1930, suggests that, given any particular niche in an environment, only one species will come to occupy that niche.

The competitive exclusion principle can be seen when we culture a mix of micro-organisms in a Petri dish. If, at first, we streak the agar properly to form multiple isolated colonies, the colonies usually coexist until they overlap, after which usually one colony type will overgrow and replace the other. Many mathematical attempts to model competition for resources in an ecosystem also suggest that one species per niche should be the end result at equilibrium.

Yet in nature, diversity prevails within most such niches. Diversity, not monoculture, is the long term norm, outside of human systematic interventions.

Why? Likely, it is because the Petri dish's zoo is artificially simplistic, as are the mathematical models. The physical environment is varied in seasons and weather, and most species have many challenges, in the physical environment and with parasite and predator, which keep that species' numbers below what is required to fully take over a given niche. This allows other species in that niche room to reproduce.

The competitive exclusion principle is thus one which applies best in artificially constrained situations, such as those created by experimental designs. A zoo is not a complete ecosystem.

Diversity may then thrive in nature in large part because of the variety of types and levels of both opportunity and adversity. When people homogenize the environment for their own purposes, we interfere with those mechanisms. The competitive exclusion principle is an anthropogenic principle.



Influence of Interspecific Competition and Landscape Structure on Spatial Homogenization of Avian Assemblages

Authors: Oliver J. Robertson, Clive McAlpine, Alan House, Martine Maron.

Published: May 28, 2013

DOI: 10.1371/journal.pone.0065299

Human-induced biotic homogenization resulting from landscape change and increased competition from widespread generalists or ‘winners’, is widely recognized as a global threat to biodiversity. However, it remains unclear what aspects of landscape structure influence homogenization. This paper tests the importance of interspecific competition and landscape structure, for the spatial homogeneity of avian assemblages within a fragmented agricultural landscape of eastern Australia. We used field observations of the density of 128 diurnal bird species to calculate taxonomic and functional similarity among assemblages. We then examined whether taxonomic and functional similarity varied with patch type, the extent of woodland habitat, land-use intensity, habitat subdivision, and the presence of Manorina colonies (a competitive genus of honeyeaters). We found the presence of a Manorina colony was the most significant factor positively influencing both taxonomic and functional similarity of bird assemblages. Competition from members of this widespread genus of native honeyeater, rather than landscape structure, was the main cause of both taxonomic and functional homogenization. These species have not recently expanded their range, but rather have increased in density in response to agricultural landscape change. The negative impacts of Manorina honeyeaters on assemblage similarity were most pronounced in landscapes of moderate land-use intensity. We conclude that in these human-modified landscapes, increased competition from dominant native species, or ‘winners’, can result in homogeneous avian assemblages and the loss of specialist species. These interacting processes make biotic homogenization resulting from land-use change a global threat to biodiversity in modified agro-ecosystems.

Toward a presumptive skepticism about the chance of globally destructive geological events

Based on the geology of impact craters and other evidence, earth science suggests that there have been about 60 very large asteroid impacts on the earth over the last 600 million years, or one impact in 10,000,000 years, a probability of (given a more than generous lifetime of 100 years) of 1 in 100,000 that there will be such an event in any given human lifetime. Since such an event would likely kill us all, this means there is a 1 in 100,000 chance of global human extinction happening in our lifetime.

Should this be something on which we should act? Compare this to the chance that our theories about such impacts are wrong. Theories in science undergo major shifts, enough to change such probability calculations significantly, at least once every 500 years. Thus, there is only 1 chance in about 200 that the above risk calculation will stand the test of geologically scaled time.

Once an event is lower in probability than the chance I may be wrong about its possibility, it is not clear whether actions based on that event becoming actual are warranted. We have to seize the days, and the consideration of extremely low probability events should not loosen our grip.

Pragmatism suggests that disease or war are the kinds of disasters that will happen, so decreasing the negative impact of war, disease, and other disasters which occur commonly during our generation on earth are practical norms.

Oliver Sacks on roles agnosia may play in neuroscience theories

First published in 1970, and still prescient today.

...our mental processes, which constitute our being and life, are not just abstract and mechanical, but personal, as well—and, as such, involve not just classifying and categorising, but continual judging and feeling also. If this is missing, we become computer-like, as Dr P. was. And, by the same token, if we delete feeling and judging, the personal, from the cognitive sciences, we reduce them to something as defective as Dr P.—and we reduce our apprehension of the concrete and real. By a sort of comic and awful analogy, our current cognitive neurology and psychology resemble nothing so much as poor Dr P.! We need the concrete and real, as he did; and we fail to see this, as he failed to see it. Our cognitive sciences are themselves suffering from an agnosia essentially similar to Dr P.’s. Dr P. may therefore serve as a warning and parable—of what happens to a science which eschews the judgmental, the particular, the personal, and becomes entirely abstract and computational.

--Oliver Sacks, The Man Who Mistook His Wife for a Hat

Pu'u 'O'o Flow Lava Ocean Entry : Drone View, 2013

Note that, as of June 2014, the lava is only burning bits of forest between Hawaii Paradise Park and Pahoa, not entering the ocean.

Eating Fruit and Vegetables Substantially Reduces Stroke Risk

This article, published online in advance in Stroke, shows that eating 2 servings a day of fruits such as citrus or salad vegetables, as well as other fruits and vegetables, can reduce risk of stroke by as much as one third. As a comparison, aspirin in a typical high risk group reduces stroke risk by 30 to 40 percent and in lesser risk groups by about 15 percent, a similar effect to this one of 2 servings a day of citrus fruit.


 2014 May 8. [Epub ahead of print]

Fruits and Vegetables Consumption and Risk of Stroke: A Meta-Analysis of Prospective Cohort Studies.


We conducted a meta-analysis to summarize evidence from prospective cohort studies about the association of fruits and vegetables consumption with the risk of stroke.


Pertinent studies were identified by a search of Embase and PubMed databases to January 2014. Study-specific relative risks with 95% confidence intervals were pooled using a random-effects model. Dose-response relationship was assessed by restricted cubic spline.


Twenty prospective cohort studies were included, involving 16 981 stroke events among 760 629 participants. The multivariable relative risk (95% confidence intervals) of stroke for the highest versus lowest category of total fruits and vegetables consumption was 0.79 (0.75-0.84), and the effect was 0.77 (0.71-0.84) for fruits consumption and 0.86 (0.79-0.93) for vegetables consumption. Subgroup and meta-regression showed that the inverse association of total fruits and vegetables consumption with the risk of stroke was consistent in subgroup analysis. Citrus fruits, apples/pears, and leafy vegetables might contribute to the protection. The linear dose-response relationship showed that the risk of stroke decreased by 32% (0.68 [0.56-0.82]) and 11% (0.89 [0.81-0.98]) for every 200 g per day increment in fruits consumption (P for nonlinearity=0.77) and vegetables consumption (P for nonlinearity=0.62), respectively.


Fruits and vegetables consumption are inversely associated with the risk of stroke.

Fingolomid and Memory Function.

Fingolomid (sold as Gilenya) is a immunomodulator taken orally once daily. It is used to prevent relapses in relapsing multiple sclerosis. Since fingolomid works by its effect on the sphingosine 1-phosphate receptor, which in lymphocytes regulates their exit from lymph nodes, it thus decreases immune cell trafficking in the brain, and thus decreases the tendency to white matter brain inflammation in MS.

However, sphingosine is also involved in many brain cell processes, including those used in processing memory. In the rodent research below, it is suggested that fingolomid might be used as a memory modulator in human conditions such as PTSD. Such effects have not, as far as I know, been seen in persons with MS, or are we not yet looking for those effects?



Active, phosphorylated fingolimod inhibits histone deacetylases and facilitates fear extinction memory

Nitai C Hait, Laura E Wise, Jeremy C Allegood, Megan O'Brien, Dorit Avni, Thomas M Reeves, Pamela E Knapp, Junyan Lu, Cheng Luo, Michael F Miles, Sheldon Milstien, Aron H Lichtman & Sarah Spiegel

Nature Neuroscience (2014) doi:10.1038/nn.3728

Received 07 March 2014 Accepted 25 April 2014 Published online 25 May 2014


FTY720 (fingolimod), an FDA-approved drug for treatment of multiple sclerosis, has beneficial effects in the CNS that are not yet well understood, independent of its effects on immune cell trafficking. We show that FTY720 enters the nucleus, where it is phosphorylated by sphingosine kinase 2 (SphK2), and that nuclear FTY720-P binds and inhibits class I histone deacetylases (HDACs), enhancing specific histone acetylations. FTY720 is also phosphorylated in mice and accumulates in the brain, including the hippocampus, inhibits HDACs and enhances histone acetylation and gene expression programs associated with memory and learning, and rescues memory deficits independently of its immunosuppressive actions. Sphk2−/− mice have lower levels of hippocampal sphingosine-1-phosphate, an endogenous HDAC inhibitor, and reduced histone acetylation, and display deficits in spatial memory and impaired contextual fear extinction. Thus, sphingosine-1-phosphate and SphK2 play specific roles in memory functions and FTY720 may be a useful adjuvant therapy to facilitate extinction of aversive memories.

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