COMPETITIVE
EXCLUSION
DYNAMICS
OF A POND ECO SYSTEM
Copyright © January, 2003, D, GRIFFITHS, ALL RIGHTS RESERVED
25:12:2002
Duncan Griffiths
Competitive exclusion (refered to here in as“CE”) is nothing new by any means, it exists all around us, it occurs in bacteria, fungi, plants and both lower and higher animals, even in commerce. CE exists everywhere every second of the day. Without it evolution would not be as advanced as it is today nor would we have so many different species inhabiting the planet.
The historic extinction of the Dinosaur's and the fact that many evolved and took to the oceans and the sky's and formed populations of birds and fishes, was as direct result of CE
Darwin spoke of CE as long ago as 1859 when he studied finches on the Galapagos Islands, in his theory “natural selection”, as one of the basic fundamentals behind the survival and evolution of the species…
Competitive Exclusion is a new tool for the koi hobbyist in helping to eliminate pathogenic bacteria from the pond eco system, and help keep our koi from harmful ulcers and infections, by the very use of such a tool we will also be excluding useful bacteria and organism's from the water column, this may be brewing a storm for potential disaster, remember, as smart as man likes to think himself in out manoeuvring Pathogens, to date humans as the *ultimate* Competitor, are at best holding our own and at worst losing the direct competitive fight with bacteria and virus.
We use antibacterial chemicals to fight bacteria and they become immune and stronger, we use antibiotics and bacteria learn real fast how to defeat this threat and again become stronger, its not unreasonable to also assume that CE will become useless as bacteria learn to deal with this threat.
Below is theory based on scientific fact on just how bacteria organism's can out manoeuvre CE when CE threatens an organism’s way of life, in more ways than you would imagine possible, but then again although CE is new to the koi hobby it is in fact as old as time itself, and far from being a new concept has been responsible for so many species living on the planet today.
It’s a fact that CE works for some hobbyists, but it’s also a fact that for some it is the start of a disaster. I realize that the article contained here in will be viewed at best controversial, but I would ask you to just keep an open mind when reading it, look at the bigger picture, and try to imagine what happens when you exclude an organism, because sure as eggs are eggs CE is not long term target specific and you will not only exclude some pathogens but also essential friendly organisms as well, its a fine Balance that holds any eco system together.
We (Humans) as a species are competing with nature by felling huge rain forests, it all seems harmless enough, but in the process complete organisms both micro and otherwise are becoming extinct and eco systems are falling apart, and the knock on effects occurs not only in the immediate vicinity of the tree losses but the failures in the eco system due to such losses can be felt thousands of miles away, Net results are a loss of vegetation and therefore animal habitats , increased desertification, global warming, and the loss of eco-organism’s and natural predation, and a complete break down of the eco systems.
These are all forms COMPETITIVE EXCLUSION.
For those who are not aware of the CE theory, CE works like this:
Imagine on an African plain roams
a strong herd of grazing animals, these animals exist on this plain by natural
events I.E. ample resource to support an unknown stable population. A plague
of locusts descends on the plain and in no time at all eat all the grazing
pastures, in this event there is no resource left for the herd and they simply
die out, or migrate to another un-utilised resource.
When this principle is applied to the pond eco system, its easy to see that we could substitute the grazing herd and
call these the pathogenic bacteria in the pond, and our bottled CE application is represented by the locust, the only difference is our bottled bugs/locusts once they have eliminated the resources cannot take flight to a new area and start over, so in the instance of the pond eco system those bugs die as well.
So for the koi hobbyist its easy to see that if you have harmful pathogenic bacteria in residence in the pond eco system, and you want to discount their numbers you can, by the use of CE, saturate the system with so called harmless bacteria that compete with the pathogenic bacteria for the limited food resource that’s available, in so doing both species scavenge the system for food till the food is exhausted then both organisms die out( in theory), you may be thinking well what happens now that your harmless bacteria in the CE application have died out?, no problem because we will be placing a weekly maintenance dose of CE in the system to mop up any newly formed food resource that has been made available from the waste by-products from the fish, thus we never allow this food source to build up to support any significant populations of pathogenic bacteria.
but remember CE is not target specific, in so much as ce will not target filter bacteria because they utilise i different foos source CE will target almost any other bacteria in th epond be they good or bad.
And here in may lie the problem. In essence this is a over simplified explanation of CE.
Competitive exclusion Terms
COMPETITION
The negative effects which one organism has upon another by consuming or controlling access to a resource that has limited availability. {Keddy 1989}
The flow of energy through Trophic levels follows the second law of thermodynamics, there is less and less energy available to each successive Trophic level, resulting in the classic Trophic level pyramid.
Important! This decline is NOT evidence that energy is lacking or not available.
Competition puts a premium on efficiency this assumes
a division or labour amongst a population and is the ultimate reason for
the amount of species we have at the present day.
If competitors
are very similar in their resource needs they may not be able to co-exist
together, one or both may become
extinct as a result of the competitive reaction = CE
principle = complete competitors cannot
co-exist
Ecologically
similar species *can* co-exist if there are 1 or more major differences in
their ecological niches
CE says that two or more species cannot co-exist on a single limited
resource in the same community " if there is no difference between the
realized niches of the two competing species, or if such differentiation is
precluded by the limitations of the habitat then one species will eliminate
and exclude the other" {Begon and Mortimer 1986}
One species
will use resource faster and more efficient than the other, thus reproduction
is more rapid, helping to eliminate the inferior competitor, this model was
derived by “Lotka a Volterra” who
modified the logistic CE to incorporate population
growth, as a result of inter-specific competition (G.F Gause) confirmed CE
in the following experiment.
Two species
of Paramecium were grown together although they both proliferated when they
occupied their own space and therefore food source, when grown together P,
Caudium was out competed and eliminated by P. Aurelia
INTER-SPECIFIC
COMPETITION
Inter-specific competition occurs when two or more species rely on the same or similar limited resources, in this case they can have a negative impact on one another, this may be in the form of interference competition {fighting} or exploitative competition {consumption or use} as the population density of one species increases it may limit the other species population.
Further
with inter-specific competition the fitness and virility of an organism is
negatively effected Therefore natural selection will favour the organism that
can escape these conditions and resource elsewhere.
Typical
example, A pack of wild dogs hunt and kill their prey for food for the pack;
if present at the time of the kill stronger predators will move in on the
kill and the dogs are driven off and are forced to watch and wait to see what's
left, when the stronger predator has eaten its fill it will move away and
allow the original hunters back to the feed, provided there are no more hunters
around higher up the Trophic level pyramid the dogs will be left the scraps
of their own kill, if there is another predator which is on a par with their
Trophic level they will fight it out for the scraps left.
So
nature has a predetermined Trophic level pyramids, an organisms position in
the pyramid is dependant on its competitive abilities therefore, dependant
on what animals are present at the dogs initial kill and at what level they
sit in the pyramid directly influences at what point in time the dogs will
be allowed back into the food chain {if ever} even if they did make the original
kill.
A case study that the koi hobbyist can relate to is; it has been known for some time that competitive exclusion exists in fish parasites in particular, Dactylogyrus.
D. anchoratus
and D. extensus are prime examples,
when both subspecies try to inhabit the same host it was found that when low
aggregates of both species were found co-existence was just possible but when
high aggregates were present, D. extensus
was the superior competitor and would exclude D. anchoratus. Making
co-existence between the two species impossible in
high numbers.
A. Ozer
Ondokuzmayis
Üniversitesi, Su Ürünleri Fakültesi, 57000 Sinop, Turkey.
Summary
Co-existence
between potentially competing species, Dactylogyrus anchoratus and D. extensus
parasitising common carp (Cyprinus carpio L) from the two localities in northern
Turkey has been studied. The distribution of these two dactylogyrids on mirror
and scaled varieties of common carp according to season and the sex of the
host at two environmentally different sampling stations is presented. Dactylogyrus
anchoratus was recorded with an infestation prevalence of 21.79% at Çobanlar
(farm) and 34.04% at Bektaºaga (lake), whilst D. extensus,
the dominant species, was recorded with infestation prevalences of 98.71%
at Çobanlar (farm) and 85.1% at Bektaºaga (lake). A possible competitive exclusion
by Dactylogyrus extensus over D. anchoratus was determined.
INTRA-SPECIFIC
COMPETITION
Intra-specific competition leads to stabile populations in that dependence of birth and death rates result in the population approaching its carrying capacity because eventual birth rates equals death rates. Limiting factors include water, space, light and food
Growth rate is slow at first due to a limited number of individuals, this is called the Lag time.
As individuals become sexually mature the population increases as the environment resource are exploited called the Exponential phase.
Carrying capacity
is reached due to limiting factors such as food , space, light and water which
results in death rates equalling
birth rates called the Stable phase
A shortage of, food, water, Light or space causes the carrying capacity to decrease the is called the Death phase where death rates exceed birth rates
The Carrying Capacity is the maximum population size an environment can support an environment that reduces birth rate is called Environmental Resistance factors such as competition disease and predation contribute to this.
An
example of intra-specific competition is in a pride of Lions, the pride will
only support one male, if two males are present they will fight sometimes
to the death or until one withdraws, this is based on pure genetics and food
resource for the pride I.E. the stronger lion survives to pass on his superior
genes to the offspring/cubs, ensuring his genetics survive and ultimately
a genetically superior Pride, and there is not enough food to support more
than the carrying capacity of the pride for the environment.
This particular
form of competition has nothing emiediatly to do with food availability although
it does have a direct baring on it,
as the female will provide all food for both the cubs and the male, this competition
is primarily to do with the male's
need to
sow his seed and ensure the survival of his genes, so much so that if a male
outsider challenges an older male in a pride and
either drives him off or kills him, the new more dominant male will kill all
the cubs of the previous male, and destroy all genetic evidence of him and
his offspring. The female after realising her cubs are gone will come into
season and be ready to mate
again in about three days, and she is happy to mate with the murderer of her
young because she realises the new male has
superior genetics.
Another example
of this directly linked to the koi hobby would be in the Biological pond filtration.
A pond filter in an ideal world would be at its biological carrying capacity
I.E. the filter is colonised with bacteria to the amount of organic waste
a population
of fish produce, (Intra-Specific competition stable phase).
If the fish population living in the eco system increases and therefore the
amount of organic waste in the water the filter population of bacteria will
grow in response, (no competition Exponential phase) however,
if the population of fish decreases and therefore the amount of organic waste
decreases the population of filter bacteria will decrease in direct response.
(Direct competition Environmental resistance).
Increased evidence
of morphological differences of an organism between species has taken place
when in direct competition in
the same habitat.
RESOURCE
PARTITIONING
Resource partitioning is the division, either artificially or naturally, of environmental resources by co-existing species so that their particular niche differs by one or more significant factors.
E.g.,
Both species access the same food source but one species favours a
portion of the source that differs significantly, either chemically or environmentally,
to that favoured by the other species.
Over
evolutionary time, competition among different species may even lead to a
shift by one (or both) species into a slightly different niche space.
Differing
subspecies of Dactylogyrus will co-exist
inter-specifically in the gill of the host, in other words differing species
of Dactylogyrus can only exist by each sub species partitioning the gill and favouring a slightly different
location of the gill
[Abstract]
SIMKOVA
A, GELNAR M, SASAL P. Aggregation of congeneric parasites (Monogenea: Dactylogyrus)
among gill microhabitats within one host species (Rutilus rutilus L.). Parasitology
2001 123 : 599-607.
Parasite
aggregation within the gill arches of 1 host species (Rutilus rutilus L.)
was studied in the case of 9 congeneric monogeneans belonging to the genus
Dactylogyrus. Both intra- and inter-specific aggregation, were followed by
considering gill arches as independent patches. Parasite species were found
to be aggregated both intra- and inter-specifically. We showed that the intensity
of parasite infection was positively related to intra-specific aggregation
only
for the more abundant species. No relationship was found between intensity
of parasite infection and niche size when correcting for total parasite intensity.
This may suggest that when parasite intensities are low, intra-specific
competition may not have a strong effect on parasites. Conversely, when looking
at the evolution of niche size and
intra-specific aggregation for each species separately, intra-specific aggregation
decreased for the most abundant
species (D. crucifer) suggesting that this species is more competitive than
others when total parasite intensity increases. When considering inter-specific
aggregation, Dactylogyrus species were found to be positively and negatively
aggregated. Following the prediction of morphological and ecological similarity
for Congeneric species, Dactylogyrus species similar in morphometry of attachment
parts tend to be more positively aggregated among their gill
microhabitats than Dactylogyrus species with morphometric differences in attachment
parts
EMIGRATION
DISPERSAL
When a resource
that two organisms compete for becomes depleted, one organism will tend to
emigrate to find another
unutilised resource in response to the difficult competition.
COMPETITIVE EXCLUSION
CE principle presumes that
one of the above situations is present and true, hence one species will always
win. However, a number of extenuating
circumstances make CE laws useless! Because
examples of excluded organisms are lost {ghosts of competition past}
these are the organism’s that were not accounted for and probably, in the
case of the pond eco-system,
many bacterial species are unknown but hold the eco-system together by their
very presence and occupation. The demands of these largely unknown and unmapped
bacteria on an eco-system result in the completion of the eco-balance.
In a pond’s eco system, CE is part of everyday life, as pond organisms compete with one another, this maintains the ecological pond balance.
This is what Dr David Moriarty of the university of Queensland wrote in an article on shrimp farming:
“Many pathogens appear to have mutated
to more virulent forms than were present a decade ago, thus aquatic
farming comes under attack even if poor water conditions are present or
not”
No surprises here.
“In Thailand this year a shrimp farmer
who was using colloidal silver in all feed stuffs experienced massive mortalities
from vibrio species this was managed by the mass introduction of Norfloxacin
in all feed, this managed the problem
very well however when all microbials stopped, all shrimp died from vibriosis
in two days, it appeared in this short
length of time a highly virulent strain of luminous vibrio sp had developed
in response to the excessive use of silver and antibiotics”.
“In Thailand its common practise to
cleanse the ponds which are sometimes one hectare in area, with chlorine,
prior to re-emptying and refilling ready for the introduction of shrimp stock
It was found that just prior to reintroduction of shrimp stock there is a massive resurgence in numbers of vibrio harveyi just after the chlorine was removed.
It’s thought that the chlorine reduces the numbers of direct and indirect competition to such an extent that they are able to increase in numbers rapidly also these were found to be more pathogenic in nature”.
This
demonstrates when an organism’s competition is excluded how fast the surviving
bacteria and possibly the pathogenic bacteria, gain ground in the eco system
“If antibiotics or antimicrobial compounds are used to reduce counts of bacteria some bacteria will survive, these will usually be found to increase in virility and numbers because they have the right genetics for survival, some of these may have escaped exclusion because they were present in a bio film in a pipe, in a filter, or on a fish or even in the gut of the fish, gram negative bacteria can and will exchanges genetics across the species and evolve rapidly”
There are several
interesting observations here, not least is the ease with which bacteria can
escape the exclusion process and the most virulent can exchange genetics across
to other non related species. And no surprise the
bacteria with the best genetics will ultimately be the best survivors.
“Resistance plasmids encoding for many
antibiotic resistant genes were transferred
between pathogenic and non pathogenic bacteria in several environments
including sea water, the rate of gene transfer between vibrio cholerae and
Aeromonas salmonicida increased 100 times
This work raises questions not only
about the use of antibiotics in aquaculture but the use of closely related
pathogenic species as probiotics. Not only antimicrobial resistant genes,
but also genes for virulence can be transferred by R plasmids and transposons.
As the R plasmids can transfer genes between widely different bacteria in
the gram negative spectrum, it was though to be extremely unwise to use Vibrio
or pseudomonas for example as probiotics”.
And finally
“Species
composition of a microbial community, such as in a pond will be determined
partly by stochastic phenomena, that is (pure chance) and partly by deterministic
and predictable factors that allow one species to grow and divide more rapidly
than others, and thus dominate numerically. Chance favours those organisms
that are in the right place at the right time to respond to a sudden increase
in nutrients e.g. from the lysis of algal cells or the decaying of waste or
unwanted food.We are still a long way away
from knowing all the factors that influence the process of competitive exclusion
and the controlling factors in the process of numeric growth rates of bacteria
undergoing competitive
exclusion because the complete species composition that make up a natural
environment in a pond eco-system are still
to a greater extent Unknown”.
how many different organisms we are excluding from a pond eco-system. From
a hobby stand point we only care as long we can influence Aeromonas and pseudomonas
count. This fact is not in dispute, as we know we can influence these two
species, but even significant reductions in these two species can give a false
sense of security.
On
an ecological time scale (i.e. within one generation of organisms), competition
will often decrease biodiversity. This is
because if two organisms are both competing for the same resource, the stronger
competitor will often win out (and drive the other population to very low
numbers - or even to zero). This phenomenon is sometimes called the CE principle.
It can be illustrated with an example:
Two
species of paramecium (paramecium are single celled organisms) are grown together
in a well-stirred flask that is regularly restocked with nutrient media. If
we follow the growth of these two populations over time, we will generally
see something like the following pattern:
The
population of species one starts off growing faster, but eventually species
2 (the better competitor) takes over, and out competes species 1 - driving
its population to zero.
This is called the Latka-Volterra model (named after two ecologists). It starts with the familiar equation for logistic growth:
And
then adds to that by including terms that account for the competitive effect
of species one on species two (and vice versa). This is in the form of two
equations, given below.
Most
of the symbols here are ones we are familiar with (N, r, t, and K). The alpha
symbol represents the effect of competition.
In the first equation, this is the effect of species two on species one. In
the second equation, alpha represents the effect of species one on species
two.
So,
if the CE principle says that when two species compete that one will perish
- why do we see so many species in nature that seem to co-exist? This is because
the natural world has more than one niche (a niche is set of resources that
an organism requires and utilizes to survive). Remember the stirred flask
mentioned above? That was an artificial environment that only contained one
functional niche - there was only one food source, and it was well mixed all
the time. Natural environments are much more heterogeneous, thus providing
more potential niches for different species to exploit. In fact, the resource
availability in an environment (i.e. its "niche space") is sometimes
called an "n-dimensional hyper-volume" - that is a "space"
of not 2 or 3 dimensions, but of some indeterminate number ("n")
- there are many axes of this "hyper-volume" and each of these axes
may represent a different resource.
Fact,
Conjecture or Theories? Take your pick!
We know for some koi keepers CE is successful in driving pathogens way down (again no argument) but we know for some it has failed to exclude pathogens sufficiently to eliminate disease or aid healing and, for some, it has apparently had disastrous consequences (showing an actual increase in disease). So for those that may of experienced poor or detrimental results when using CE, Below is some theory based on this same science that may help in some way to explain why it sometimes does not work.
If we think back to the locust example, in the pond eco system we now have to factor the following extenuating circumstances into the equation.
The introduction of CE could result in natural and essential Bacteria in the fishes gut being out competed, which results in increased food passage as the bacterial competition increases the need for nutrients. Net result not only would this have a negative impact on essential bacteria, the total population of bacteria would compete with the host (fish) for nutrients from the food it eats( as the food source we are trying to eliminate are in the main carbon based) , further the reduced number of natural essential bacteria would result in reduced production of bacterial by-products essential to optimum intestinal function; is reduced and caan lead to a reduced immune system.
It’s common knowledge that bacteria can be out competed in the water column
but there is a possibility they cannot be out competed in the mucus layer,
because of the biological make up of the mucus layer results in a food source
in the mucus and this is constantly being replenished I.E. sloughing off of
dead host cells, whilst its generally agreed that the mucus layer in an aquatic
Teleosts incorporates natural immune antibodies these are a general antibody
of antigens found commonly occurring in nature and are not as a result of
previously encountered pathogenic antigens, they will inhibit but not eliminate
all bacteria
The most virulent strains, are amongst the strongest competitors and are most likely to be the main survivors of CE only now we have upset the eco- balance, we have eliminated the competition! {The ghosts of CE}
When using CE for the first time, some hobbyists have taken base line readings of Aeromonas and Pseudomonas, e.g., a reading for a typical pre treated pond might be something like 150,000 CFUs (colony forming units) per cc of water. This would be pathogenic Aeromonas and Pseudomonas combined. But, we usually don’t check for the presence of other organisms or bacteria in the eco-system, or even what variety and strains of anaerobes (Yes Anaerobes) that is present in any typical CE application that we are about to use. In truth in a typical pond eco-system, we do not know what all the beneficial organisms that are present, because they are simply not all mapped.
So as previously mentioned after a typical treatment, we have absolutely no idea what the GHOSTS OF CE were! Why? Because we never check! We send our after sample off to the lab and only check for Aeromonas and Pseudomonas. And, its no secret or surprise even to sceptics that we can significantly reduced these counts to say sub 25000 CFUs per cc. But we never know by how much we have reduced the numeric count of other species of bacterial (or their types) that are essential in keeping the eco system balanced and therefore go some way towards holding Aeromonas and Pseudomonas in check. Remember this is all part of natural competition. Further, we don’t know how much of the so-called useful bacteria in the CE application is left. We assume none.
Neither do we know how much, if at all, we have diminished the essential bacteria of the gut. The maker’s of the CE products only claim is that nitrifying bacteria are unaffected. I would say that some important questions are unanswered?
If
the numeric counts of these later bacteria of the non-pathogenic kind is a
figure near zero, we could have created an ecological problem in the pond.
A proposition not so unreasonable given the opinions above by scientists
that pathogenic bacteria are given to such virulence that they can out compete
out grow and out number most non-pathogenic bacteria given even half a chance
Therefore, this would seem to be an acceptable thesis based on current
available science.
We do know that most pathogenic bacteria favour differing sites and forms
of attack, so it follows that they cannot all occupy the same niche in the
eco-system, this is of particular interest as the principles of CE Says two
organisms cannot co-exist in the same niche! And presumes that CE competes
with pathogens in one Niche or another not both? Which I would presume would
tip a so-called level playing field in favour of harmless bacteria or pathogenic
bacteria as far as CE is concerned.
Assuming
we have by the use of CE significantly reduced a typical numeric count of
Aeromonas and pseudomonas to a figure of sub 25000 CFUs. Adding to this we know we probably cannot influence
the numeric count in mucus coat of the fish or the filters or the walls of
the pond or the fish.. The final hypothetical tested numeric figure of 25000
cfu’s per cc of water, would be for Aeromonas and Pseudomonas and would be
obtained purely from the water column because that’s what we ask of the laboratory.
This figure would not be obtained from the mucus layer of the fish the filter
media or pipes or pond walls, which could possibly multiply that figure by
factor of who knows? Only
now we have now eliminated the competition for these pathogenic bacteria?
The
above does not figure into the equation such occurrences as quality control
or pathogenic bacteria being contained in the bottle and therefore adding
to the pathogenic load in the eco- system and/or storage problems! Or even
dare I say, some form of CE taking place right there in the bottle, leaving
the contents minus some or most of the species it should have contained, after
all if you buy into the fact that CE is a capable application you also have
to buy into the fact CE *CAN* take place within the stored species of bacteria
in the bottle if left for some time and not in the right environmental conditions
I.E refrigerated or with the top loose?
I will leave it here as this was one of those projects that once I got into the research it found it was a huge-massive subject, it was like looking into a hole and the more you looked the bigger the hole got,
But I hope it has stimulated your interest and interested you enough that you would like to know more, to say this subject is big is an understatement. But I will leave it with these final few words,
Nature abhors a vacuum. If a resource is un-utilized or under utilized, natural events usually take place to bring the situation back into "balance." We sometimes may not like nature’s way of balancing out the equation.
Duncan