The Lone Ranger
07-15-2007, 02:14 AM
One reason I care little for most “nature shows” is because they so-often give a very misleading impression of how things work. Everyone’s familiar with the adage “Nature red in tooth and claw,” for instance, and many seem think it originated in Darwin’s Origin of Species. Actually, it’s from Alfred, Lord Tennyson’s poem In Memoriam A.H.H..
I suppose footage of lions ripping apart zebras grabs the attention in a way that few other things can, and perhaps that’s why so many nature documentaries seem to concentrate on the more brutal aspects of animals’ lives. Still, it creates the false impression that animals spend their entire lives in a “kill or be killed” state – constantly engaged in attacking others and/or defending themselves from attackers. But that isn’t the reality. [The opposite extreme, so often seen in Disney films – that animals live in some sort of happy paradise and spend all day frolicking unless disturbed by "Man" – is just as misleading.]
In fact, despite the fact that such documentaries tend to stress competition above all else, organisms – even organisms of completely unrelated species – very often work together and thus achieve goals that neither could achieve on its own. In fact, some evolutionary theorists argue that cooperation between organisms and species is a more important factor driving evolution than is competition within and between species.
Consider bacteria, if you will. Bacteria (and Archaea) are prokaryotes. A prokaryotic organism has small, relatively simple cells that lack nuclei or other membrane-bound organelles. By contrast, a eukaryote is an organism that has relatively large and much more complex cells that have nuclei, mitochondria, and other membrane-bound organelles. All multicellular organisms are eukaryotes, including all Protists, Fungi, Plants, and Animals.
Evidently, there are some disadvantages to having small, very simple cells. Nonetheless, the bacteria are quite successful. Some are aerobes that can use oxygen to chemically break down glucose and other carbohydrates for energy. Others (the cyanobacteria) can do the opposite – they capture solar energy and use it to combine CO2 and water to make glucose in the process of photosynthesis.
What has this to do with cooperation as a driver of evolutionary change, you wonder? Well, it’s not uncommon for small bacterial cells to invade larger cells. Sometimes the larger cell manages to destroy the invader. Sometimes the invader winds up killing the larger cell. But every so often, it seems to happen that the invading cell does the larger cell no harm, and the larger cell doesn’t destroy the invader. This has occasionally been seen when bacterial cells invade an amoeba. Apparently, if the bacteria do the amoeba no harm, the amoeba doesn’t necessarily mount an “immune response” to get rid of them.
Well, as it turns out, all eukaryotic cells have structures inside of them known as mitochondria. These structures allow our cells to utilized oxygen to break down glucose for energy – just like aerobic bacteria do. In fact, mitochondria are about the same size as are aerobic bacteria, and they look like them, too. What’s more, mitochondria have their own DNA and replicate (more or less) independently of the rest of the cell. When you examine that mitochondrial DNA, it turns out to be much more similar to bacterial DNA than the DNA in the nucleus of the cell.
In other words, the mitochondria in our cells – which make it possible for us to use oxygen in order to generate energy – are almost certainly the descendants of bacterial cells that invaded larger cells in the distant past. The arrangement evidently turned out to be mutually beneficial, as the larger cells provided the aerobic bacteria with food and protection, and the bacteria provided the larger cells with energy.
The cells of algae and plants have organelles inside of them called chloroplasts, which look just like cyanobacteria. Again, they have their own DNA, and it closely resembles that of cyanobacteria. So, the chloroplasts in algal and plant cells are almost certainly the results of bacterial cells invading larger cells and the arrangement turning out to be mutually beneficial.
In short, the origin of eukaryotic cells – often touted as the single most significant event in the evolution of life on Earth – is the supreme example of cooperation between different species. The mitochondria and chloroplasts have become so completely integrated into their host cells that neither mitochondria nor chloroplasts can survive independently of their host cells – and neither can the host cells survive without their “little guests.”
http://www.eecs.berkeley.edu/Programs/doublex/spring03/strawberrydna_files/image003.jpg
A typical plant cell. The mitochondria and chloroplasts are, in effect, smaller cells living inside the larger cell.
Examples of cooperative relationships between unrelated species aren’t at all difficult to find, but such relationships are apparently much less exciting than competitive relationships or predator/prey relationships. Perhaps this is one reason why they’re so rarely highlighted in nature documentaries.
Darwin pointed out that no behavior could evolve for the benefit of a different species. That is, if you want to understand why an organism of “Species A” behaves in a way that benefits “Species B,” you have to figure out why it benefits individuals of “Species A” to behave that way. That’s a point worth keeping in mind: what may superficially look like “altruistic” or “cooperative” behavior evolves if and only if it benefits the individuals performing the behavior. It is quite irrelevant to bees that flowers happen to benefit from their actions, for instance – what matters from the perspective of the evolution of bee behavior is that the bees benefit from this behavior.
Take the existence of cleaner fishes. Various small fish species, notably species in the wrasse family, have specialized as “cleaners” of larger fishes. The cleaners are very distinctively-colored, and they often take up permanent residence near easily-located landmarks such as coral outcrops, which makes it easy for their “clients” to find them. Larger fishes will come to these “cleaning stations” – sometimes from considerable distances – and, when they see the cleaner, will adopt a very characteristic pose. They drop their pectoral fins and open their mouths and opercula (gill covers), and hang more or less motionless in the water. The cleaner fish will approach the client fish and pick off parasites or patches of dead skin. What’s really remarkable about this relationship is that the client fish will often allow the cleaner to swim into its mouth unharmed, and even into its very sensitive gills.
It’s quite an impressive example of cooperative behavior between unrelated species. It works, of course, because both species benefit from the arrangement. The cleaner fish are not attacked by larger fishes; on the contrary, they can approach most larger fishes with impunity. The cleaners get food, and the client fishes have parasites and dead skin (which might otherwise become infected) removed. So, each species benefits from the arrangement.
http://www.amonline.net.au/FISHES/fishfacts/images/cleangt2.jpg
Cleaner wrasses working on a goatfish client.
The arrangement is not flawless, of course. There are a number of small fish species that look and behave remarkably like cleaner fishes. They use their resemblance to cleaner fishes to approach unsuspecting larger fishes. When the larger fish sees what appears to be a cleaner fish approaching, it relaxes and adopts the distinctive “clean me” pose. Instead of cleaning the other fish, however, the cleaner-fish mimic darts in and bites off a chunk of flesh from the larger fish, then darts away before it can retaliate.
http://www.nature.com/nature/journal/v433/n7023/images/433211a-f1.2.jpg
In this picture, a is a species of fangblenny that mimics cleaner wrasses and uses its
resemblance to them to prey upon larger fishes.
The fish in Picture b is the cleaner wrasse that the fangblenny mimics, hard at work.
The fishes in Pictures c and d are fangblennies that don't mimic cleaner wrasses.
This sort of complex relationship between three unrelated fish species is exactly the sort of thing that creationists insist could never evolve. After all, large fish species normally eat smaller fishes, and smaller fishes – quite sensibly – normally avoid larger fishes precisely that reason. So how did the larger fish species evolve the behavior to allow cleaners to approach and clean them? How did the ancestors of the cleaner fishes evolve such a strange behavior – actually approaching larger fishes that might eat them? Why are the cleaners so distinctly-colored, and why do the mimics look almost identical to them?
“Obviously,” creationists say, “this kind of complex relationship couldn’t have evolved in a gradual, stepwise manner, because it couldn’t work unless all the behaviors were in place.”
That view reflects a poverty of imagination. Or perhaps, an unwillingness to think too hard about how such an arrangement might evolve. I give this exercise to my “Evolution for Non-Majors” course and they rarely have any problems explaining how such an arrangement could evolve.
First of all, larger fishes don’t just mindlessly vacuum up any smaller fish that gets within range. Anyone who’s spent much time at a public aquarium and seen sharks and barracudas swimming with much smaller reef fish knows that. By and large, when an animal has a full belly and isn’t hungry, it’s pretty harmless and can be all but ignored by potential prey. In fact, it’s not an unusual sight on the African plains to see antelopes following lions. More to the point, perhaps, next time you watch a nature documentary, you may have noticed that when a lion or cheetah chases down an antelope, when it catches one, the rest of the herd stops running. There’s no point in running from a predator that already has its prey and/or that you know isn’t hungry. One hypothesis regarding why prey species sometimes actually follow their predators has to do with the fact that most predators are highly territorial. If a pride of lions has recently made a kill, it may actually be in the surviving prey animals’ best interests to remain fairly close to those lions (which are, for the moment, not a danger), rather than wander too far away and perhaps into the territory of another pride of lions – lions that might not have fed recently, and so will be in search of prey.
The general point is that predators that are actively hunting tend to look and behave quite differently from predators that are sated and not a threat. [When they are hungry, many predators will eat until sated. Therefore, their bellies will be fully and noticeably distended. You can often tell whether a lion, for example, has made a kill recently just from looking at its belly.] And predators that aren’t actively hunting are often relatively safe to approach.
In fact, many smaller fishes will approach larger fishes – from behind, if possible, where they’re less likely to be seen – and snatch off a parasite for food. Or a chunk of flesh.
So, the first step is already in place. Many smaller fishes will approach larger fishes in search of food. If most of the fish that do so are picking off parasites or dead skin, it’s likely in the larger fish’s best interest to allow the smaller fishes to approach. So, selection would tend to favor tolerance on the larger fish’s part – up to a point, anyway.
Since larger fish represented an easy and abundant source of food for the ancestors of cleaner fishes, there would be selection for them to approach larger fishes to pick off parasites and dead skin – so long as the risk of being attacked did not outweigh the benefit of having access to food. And, of course, the cleaner-fish ancestors would be expected to be very sensitive to the behavior of larger fishes, and would not be expected to approach fishes that appeared to be hungry or otherwise intolerant of approach.
Both species would benefit; the cleaner-fish ancestors would gain food and the client fish would have harmful parasites and dead skin removed. It’s very-definitely in the best interest of the client fish to allow cleaners to approach – but how to tell the cleaners from other small fish? It’s not like the larger fish can adopt a strategy of “avoid eating any smaller fishes”; it’ll starve. On the other hand, if it can somehow tell which fish are cleaners and which are not, it’ll have a means of avoiding eating cleaners (and, it’ll also be less likely to allow small fish to approach that want to take a bite out of it).
Any genetic mutation which happens to make the cleaner fish easy to recognize will have the happy coincidence of benefiting both the cleaner fish and the client species. So, there will be selection both for cleaner fish to be easy to recognize and for client fishes to allow any fishes it recognizes as cleaners to approach.
In fact, though the relationship between the cleaner and the client is cooperative, there most-definitely is an element of competition involved. Cleaner fish that are easy to recognize are less likely to be attacked, and so any mutation that makes its bearers easy to recognize as cleaners (as opposed to either predators or prey) will tend to spread through the cleaner fish population. Similarly, client fish that can learn to recognize cleaners are more likely to survive and reproduce, because they’ll have more parasites and potentially-infected patches of dead skin removed.
So, there is competition among cleaner fish to be easily recognized for what they are – the most easily-recognized individuals will tend to be the best-fed and least subject to attack from larger fishes. There is also competition between client fish to be able to accurately distinguish between cleaners and other small fish – those that are best at doing so will tend to live longer, since they’ll be healthier on average.
Once the cleaner fish/client system is in place, there will be competition among small predatory fish to look more and more like cleaners, so that they can exploit the client species’ “trust” of cleaner fish to get close-enough to snatch a bite.
There are plenty of other examples of different species evolving to cooperate with each other. For example, a number of bird species specialize in removing ticks and other parasites from large mammals, in much the same way that cleaner fish remove parasites from larger fishes. Starlings of the genus Buphagus – especially Buphagus africanus and Buphagus erythrorhyncus – are commonly called “tickbirds” or “oxpeckers,” and can often be seen riding around on the backs of giraffes, wildebeests, etc., picking off ticks and other parasites. The “crocodile bird,” Pluvianus aegyptius, is often seen plucking parasites off the hides of Nile crocodiles, and will even enter a crocodile’s mouth to pick bits of rotting flesh from between its teeth.
http://www.wildlife-pictures-online.com/image-files/impala_knp-9113_blog.jpg
A red-billed oxpecker servicing a young impala.
http://www.warrenphotographic.co.uk/photography/cats/00955.jpg
A “crocodile bird” at work.
Many, many plants “cooperate” with animals in one way or another. The flowers of a great many plants are pollinated by animals, for instance, and coevolution between flowering plants and their insect pollinators has been a major factor in the evolution of both groups. Many flowering plants, famously, produce nectar which attracts insects, birds, or bats. The insect, bird or bat gets a high-energy meal, and the flower gets pollinated in return, so each species benefits by “cooperating with” the other.
http://www.schmoker.org/BirdPics/Photos/Hummingbirds/RUHUfly2.jpg
A female rufous hummingbird feeding on nectar – and, incidentally, pollinating the flower.
Ants are among the most common of insects, and there are many ways in which plants and ants cooperate with each other. For instance, the seeds of many plants have fat-rich structures attached called eliasomes, which attract ants. The ants harvest these seeds and store them in their underground nests. The ants get a good meal from the eliasome, and, in burying the seed underground, they plant it. Many other plant species rely upon animals to disperse their seeds in similar manners.
Some trees have hollowed-out branches in which ants live. Some even go so far as to secrete sweet sap which attracts ants and encourages them to take up residence inside the tree. The ants patrol the tree and pick off any leaf-munching caterpillars or other insects they may encounter. If a giraffe or other large herbivore attacks the tree, the ants swarm out and sting it, encouraging it to move on and leave the tree alone.
Some ants are farmers. Some harvest fungi and grow them in their nests, “fertilizing” them with fecal matter. They then “harvest” the fungi for food. There are some fungus species that are not known to grow anywhere else except for ant nests.
A number of ant species “farm” aphids. Aphids are small insects that feed on the sap of plants. Some ant species tend aphids very-much like we tend sheep or cows. The ants protect the aphids from predators and even carry them from place to place. When hungry, an ant rubs the aphid with its feelers, and the aphid secretes a drop of “honeydew” (concentrated sap), which the ant consumes.
http://www.ent.iastate.edu/images/homoptera/aphid/soybeanaphid/aphidant.jpg
An ant tending its aphid flock.
A lichen is a superb example of cooperation between unrelated organisms. A lichen is not one organism, but two. It is a fungus and a green alga (or a cyanobacterium) growing together. The fungal mycelium provides the alga with water and protection, while the algal cells provide the fungus with food. As a result of this immensely successful partnership, lichens can be found in some of the harshest environments on Earth – growing on rocks in Antarctica where it’s too cold for any other living things, and in blazing-hot, water-less deserts.
http://bugs.bio.usyd.edu.au/Mycology/images/Topics/Plant_Interactions/Lichens/yellowLichen.jpg
Lichens are among the most durable organisms on the planet,
and often grow on bare rock.
Nature is by no means always “red in tooth and claw.”
Cheers,
Michael
I suppose footage of lions ripping apart zebras grabs the attention in a way that few other things can, and perhaps that’s why so many nature documentaries seem to concentrate on the more brutal aspects of animals’ lives. Still, it creates the false impression that animals spend their entire lives in a “kill or be killed” state – constantly engaged in attacking others and/or defending themselves from attackers. But that isn’t the reality. [The opposite extreme, so often seen in Disney films – that animals live in some sort of happy paradise and spend all day frolicking unless disturbed by "Man" – is just as misleading.]
In fact, despite the fact that such documentaries tend to stress competition above all else, organisms – even organisms of completely unrelated species – very often work together and thus achieve goals that neither could achieve on its own. In fact, some evolutionary theorists argue that cooperation between organisms and species is a more important factor driving evolution than is competition within and between species.
Consider bacteria, if you will. Bacteria (and Archaea) are prokaryotes. A prokaryotic organism has small, relatively simple cells that lack nuclei or other membrane-bound organelles. By contrast, a eukaryote is an organism that has relatively large and much more complex cells that have nuclei, mitochondria, and other membrane-bound organelles. All multicellular organisms are eukaryotes, including all Protists, Fungi, Plants, and Animals.
Evidently, there are some disadvantages to having small, very simple cells. Nonetheless, the bacteria are quite successful. Some are aerobes that can use oxygen to chemically break down glucose and other carbohydrates for energy. Others (the cyanobacteria) can do the opposite – they capture solar energy and use it to combine CO2 and water to make glucose in the process of photosynthesis.
What has this to do with cooperation as a driver of evolutionary change, you wonder? Well, it’s not uncommon for small bacterial cells to invade larger cells. Sometimes the larger cell manages to destroy the invader. Sometimes the invader winds up killing the larger cell. But every so often, it seems to happen that the invading cell does the larger cell no harm, and the larger cell doesn’t destroy the invader. This has occasionally been seen when bacterial cells invade an amoeba. Apparently, if the bacteria do the amoeba no harm, the amoeba doesn’t necessarily mount an “immune response” to get rid of them.
Well, as it turns out, all eukaryotic cells have structures inside of them known as mitochondria. These structures allow our cells to utilized oxygen to break down glucose for energy – just like aerobic bacteria do. In fact, mitochondria are about the same size as are aerobic bacteria, and they look like them, too. What’s more, mitochondria have their own DNA and replicate (more or less) independently of the rest of the cell. When you examine that mitochondrial DNA, it turns out to be much more similar to bacterial DNA than the DNA in the nucleus of the cell.
In other words, the mitochondria in our cells – which make it possible for us to use oxygen in order to generate energy – are almost certainly the descendants of bacterial cells that invaded larger cells in the distant past. The arrangement evidently turned out to be mutually beneficial, as the larger cells provided the aerobic bacteria with food and protection, and the bacteria provided the larger cells with energy.
The cells of algae and plants have organelles inside of them called chloroplasts, which look just like cyanobacteria. Again, they have their own DNA, and it closely resembles that of cyanobacteria. So, the chloroplasts in algal and plant cells are almost certainly the results of bacterial cells invading larger cells and the arrangement turning out to be mutually beneficial.
In short, the origin of eukaryotic cells – often touted as the single most significant event in the evolution of life on Earth – is the supreme example of cooperation between different species. The mitochondria and chloroplasts have become so completely integrated into their host cells that neither mitochondria nor chloroplasts can survive independently of their host cells – and neither can the host cells survive without their “little guests.”
http://www.eecs.berkeley.edu/Programs/doublex/spring03/strawberrydna_files/image003.jpg
A typical plant cell. The mitochondria and chloroplasts are, in effect, smaller cells living inside the larger cell.
Examples of cooperative relationships between unrelated species aren’t at all difficult to find, but such relationships are apparently much less exciting than competitive relationships or predator/prey relationships. Perhaps this is one reason why they’re so rarely highlighted in nature documentaries.
Darwin pointed out that no behavior could evolve for the benefit of a different species. That is, if you want to understand why an organism of “Species A” behaves in a way that benefits “Species B,” you have to figure out why it benefits individuals of “Species A” to behave that way. That’s a point worth keeping in mind: what may superficially look like “altruistic” or “cooperative” behavior evolves if and only if it benefits the individuals performing the behavior. It is quite irrelevant to bees that flowers happen to benefit from their actions, for instance – what matters from the perspective of the evolution of bee behavior is that the bees benefit from this behavior.
Take the existence of cleaner fishes. Various small fish species, notably species in the wrasse family, have specialized as “cleaners” of larger fishes. The cleaners are very distinctively-colored, and they often take up permanent residence near easily-located landmarks such as coral outcrops, which makes it easy for their “clients” to find them. Larger fishes will come to these “cleaning stations” – sometimes from considerable distances – and, when they see the cleaner, will adopt a very characteristic pose. They drop their pectoral fins and open their mouths and opercula (gill covers), and hang more or less motionless in the water. The cleaner fish will approach the client fish and pick off parasites or patches of dead skin. What’s really remarkable about this relationship is that the client fish will often allow the cleaner to swim into its mouth unharmed, and even into its very sensitive gills.
It’s quite an impressive example of cooperative behavior between unrelated species. It works, of course, because both species benefit from the arrangement. The cleaner fish are not attacked by larger fishes; on the contrary, they can approach most larger fishes with impunity. The cleaners get food, and the client fishes have parasites and dead skin (which might otherwise become infected) removed. So, each species benefits from the arrangement.
http://www.amonline.net.au/FISHES/fishfacts/images/cleangt2.jpg
Cleaner wrasses working on a goatfish client.
The arrangement is not flawless, of course. There are a number of small fish species that look and behave remarkably like cleaner fishes. They use their resemblance to cleaner fishes to approach unsuspecting larger fishes. When the larger fish sees what appears to be a cleaner fish approaching, it relaxes and adopts the distinctive “clean me” pose. Instead of cleaning the other fish, however, the cleaner-fish mimic darts in and bites off a chunk of flesh from the larger fish, then darts away before it can retaliate.
http://www.nature.com/nature/journal/v433/n7023/images/433211a-f1.2.jpg
In this picture, a is a species of fangblenny that mimics cleaner wrasses and uses its
resemblance to them to prey upon larger fishes.
The fish in Picture b is the cleaner wrasse that the fangblenny mimics, hard at work.
The fishes in Pictures c and d are fangblennies that don't mimic cleaner wrasses.
This sort of complex relationship between three unrelated fish species is exactly the sort of thing that creationists insist could never evolve. After all, large fish species normally eat smaller fishes, and smaller fishes – quite sensibly – normally avoid larger fishes precisely that reason. So how did the larger fish species evolve the behavior to allow cleaners to approach and clean them? How did the ancestors of the cleaner fishes evolve such a strange behavior – actually approaching larger fishes that might eat them? Why are the cleaners so distinctly-colored, and why do the mimics look almost identical to them?
“Obviously,” creationists say, “this kind of complex relationship couldn’t have evolved in a gradual, stepwise manner, because it couldn’t work unless all the behaviors were in place.”
That view reflects a poverty of imagination. Or perhaps, an unwillingness to think too hard about how such an arrangement might evolve. I give this exercise to my “Evolution for Non-Majors” course and they rarely have any problems explaining how such an arrangement could evolve.
First of all, larger fishes don’t just mindlessly vacuum up any smaller fish that gets within range. Anyone who’s spent much time at a public aquarium and seen sharks and barracudas swimming with much smaller reef fish knows that. By and large, when an animal has a full belly and isn’t hungry, it’s pretty harmless and can be all but ignored by potential prey. In fact, it’s not an unusual sight on the African plains to see antelopes following lions. More to the point, perhaps, next time you watch a nature documentary, you may have noticed that when a lion or cheetah chases down an antelope, when it catches one, the rest of the herd stops running. There’s no point in running from a predator that already has its prey and/or that you know isn’t hungry. One hypothesis regarding why prey species sometimes actually follow their predators has to do with the fact that most predators are highly territorial. If a pride of lions has recently made a kill, it may actually be in the surviving prey animals’ best interests to remain fairly close to those lions (which are, for the moment, not a danger), rather than wander too far away and perhaps into the territory of another pride of lions – lions that might not have fed recently, and so will be in search of prey.
The general point is that predators that are actively hunting tend to look and behave quite differently from predators that are sated and not a threat. [When they are hungry, many predators will eat until sated. Therefore, their bellies will be fully and noticeably distended. You can often tell whether a lion, for example, has made a kill recently just from looking at its belly.] And predators that aren’t actively hunting are often relatively safe to approach.
In fact, many smaller fishes will approach larger fishes – from behind, if possible, where they’re less likely to be seen – and snatch off a parasite for food. Or a chunk of flesh.
So, the first step is already in place. Many smaller fishes will approach larger fishes in search of food. If most of the fish that do so are picking off parasites or dead skin, it’s likely in the larger fish’s best interest to allow the smaller fishes to approach. So, selection would tend to favor tolerance on the larger fish’s part – up to a point, anyway.
Since larger fish represented an easy and abundant source of food for the ancestors of cleaner fishes, there would be selection for them to approach larger fishes to pick off parasites and dead skin – so long as the risk of being attacked did not outweigh the benefit of having access to food. And, of course, the cleaner-fish ancestors would be expected to be very sensitive to the behavior of larger fishes, and would not be expected to approach fishes that appeared to be hungry or otherwise intolerant of approach.
Both species would benefit; the cleaner-fish ancestors would gain food and the client fish would have harmful parasites and dead skin removed. It’s very-definitely in the best interest of the client fish to allow cleaners to approach – but how to tell the cleaners from other small fish? It’s not like the larger fish can adopt a strategy of “avoid eating any smaller fishes”; it’ll starve. On the other hand, if it can somehow tell which fish are cleaners and which are not, it’ll have a means of avoiding eating cleaners (and, it’ll also be less likely to allow small fish to approach that want to take a bite out of it).
Any genetic mutation which happens to make the cleaner fish easy to recognize will have the happy coincidence of benefiting both the cleaner fish and the client species. So, there will be selection both for cleaner fish to be easy to recognize and for client fishes to allow any fishes it recognizes as cleaners to approach.
In fact, though the relationship between the cleaner and the client is cooperative, there most-definitely is an element of competition involved. Cleaner fish that are easy to recognize are less likely to be attacked, and so any mutation that makes its bearers easy to recognize as cleaners (as opposed to either predators or prey) will tend to spread through the cleaner fish population. Similarly, client fish that can learn to recognize cleaners are more likely to survive and reproduce, because they’ll have more parasites and potentially-infected patches of dead skin removed.
So, there is competition among cleaner fish to be easily recognized for what they are – the most easily-recognized individuals will tend to be the best-fed and least subject to attack from larger fishes. There is also competition between client fish to be able to accurately distinguish between cleaners and other small fish – those that are best at doing so will tend to live longer, since they’ll be healthier on average.
Once the cleaner fish/client system is in place, there will be competition among small predatory fish to look more and more like cleaners, so that they can exploit the client species’ “trust” of cleaner fish to get close-enough to snatch a bite.
There are plenty of other examples of different species evolving to cooperate with each other. For example, a number of bird species specialize in removing ticks and other parasites from large mammals, in much the same way that cleaner fish remove parasites from larger fishes. Starlings of the genus Buphagus – especially Buphagus africanus and Buphagus erythrorhyncus – are commonly called “tickbirds” or “oxpeckers,” and can often be seen riding around on the backs of giraffes, wildebeests, etc., picking off ticks and other parasites. The “crocodile bird,” Pluvianus aegyptius, is often seen plucking parasites off the hides of Nile crocodiles, and will even enter a crocodile’s mouth to pick bits of rotting flesh from between its teeth.
http://www.wildlife-pictures-online.com/image-files/impala_knp-9113_blog.jpg
A red-billed oxpecker servicing a young impala.
http://www.warrenphotographic.co.uk/photography/cats/00955.jpg
A “crocodile bird” at work.
Many, many plants “cooperate” with animals in one way or another. The flowers of a great many plants are pollinated by animals, for instance, and coevolution between flowering plants and their insect pollinators has been a major factor in the evolution of both groups. Many flowering plants, famously, produce nectar which attracts insects, birds, or bats. The insect, bird or bat gets a high-energy meal, and the flower gets pollinated in return, so each species benefits by “cooperating with” the other.
http://www.schmoker.org/BirdPics/Photos/Hummingbirds/RUHUfly2.jpg
A female rufous hummingbird feeding on nectar – and, incidentally, pollinating the flower.
Ants are among the most common of insects, and there are many ways in which plants and ants cooperate with each other. For instance, the seeds of many plants have fat-rich structures attached called eliasomes, which attract ants. The ants harvest these seeds and store them in their underground nests. The ants get a good meal from the eliasome, and, in burying the seed underground, they plant it. Many other plant species rely upon animals to disperse their seeds in similar manners.
Some trees have hollowed-out branches in which ants live. Some even go so far as to secrete sweet sap which attracts ants and encourages them to take up residence inside the tree. The ants patrol the tree and pick off any leaf-munching caterpillars or other insects they may encounter. If a giraffe or other large herbivore attacks the tree, the ants swarm out and sting it, encouraging it to move on and leave the tree alone.
Some ants are farmers. Some harvest fungi and grow them in their nests, “fertilizing” them with fecal matter. They then “harvest” the fungi for food. There are some fungus species that are not known to grow anywhere else except for ant nests.
A number of ant species “farm” aphids. Aphids are small insects that feed on the sap of plants. Some ant species tend aphids very-much like we tend sheep or cows. The ants protect the aphids from predators and even carry them from place to place. When hungry, an ant rubs the aphid with its feelers, and the aphid secretes a drop of “honeydew” (concentrated sap), which the ant consumes.
http://www.ent.iastate.edu/images/homoptera/aphid/soybeanaphid/aphidant.jpg
An ant tending its aphid flock.
A lichen is a superb example of cooperation between unrelated organisms. A lichen is not one organism, but two. It is a fungus and a green alga (or a cyanobacterium) growing together. The fungal mycelium provides the alga with water and protection, while the algal cells provide the fungus with food. As a result of this immensely successful partnership, lichens can be found in some of the harshest environments on Earth – growing on rocks in Antarctica where it’s too cold for any other living things, and in blazing-hot, water-less deserts.
http://bugs.bio.usyd.edu.au/Mycology/images/Topics/Plant_Interactions/Lichens/yellowLichen.jpg
Lichens are among the most durable organisms on the planet,
and often grow on bare rock.
Nature is by no means always “red in tooth and claw.”
Cheers,
Michael