Supplemental Lecture (97/05/03 update) by Stephen T. Abedon (abedon.1@osu.edu)

  1. Chapter title: Specific Interactions
    1. A list of vocabulary words is found toward the end of this document
  2. Niche
    1. An organisms "job":
      1. A niche essentially is an organism's life "job".
      2. That is, a niche is what an organism does, and when, where it does it.
    2. Requirements for survival:
      1. All parameters relevant to an organism for its survival and reproduction must exist at at least satisfactory levels for populations to survive and prosper.
      2. All of these parameters as well as what an organism does with them help define an organism's niche.
  3. Fundamental [theoretical] niche
    1. A Fundamental (or theoretical) niche is the full spectrum of resources potentially available to an organism, should those resources exist and are not utilized by organisms of other species.
    2. An unrealizable ideal:
      1. The fundamental nicheis an ideal not realized by organisms in practice.
      2. That is, in practice all of the resources which an organism could conceivably exploit will either not be available at all or will be exploited as well by other organisms, many of which are as good or better at exploiting any given resourse.
  4. Realized [actual] niche
    1. The realized (or actual) niche is the resources actually available to an organism, particularly given the occurrence of other species also capable of utilizing those various resources.
    2. Fewer resources:
      1. The realized niche tends to be less broad than the fundamental niche.
      2. The realized niche is essentially equivalent to what you could accomplish if you had lots of money (fundamental niche) and what you can accomplish in the absence of lots of money (realized niche).
  5. Competitive exclusion
    1. Limiting resources:
      1. Competitive exclusion is the principle that states that two species cannot compete indefinitely for the same limiting resource. One of the two species inevitably is out competed by the other, and consequently goes extinct.
      2. An absence of extinction is consistent with the limiting resource not really being limiting, or the two species not really being two different species after all.
    2. Another way of saying this is that the two niches associated with two indefinitely coexisting species cannot completely overlap.
  6. Intraspecific competition
    1. Same species niches can overlap:
      1. Intraspecific competition does not lead to competitive exclusion.
      2. The niches associated with two coexisting members of the same species can completely overlap without driving the species itself extinct.
      3. That is, the degree to which conspecifics compete is greater than even that which can occur between species (by definition if you consider the ecological species concept).
    2. Microevolution:
      1. Intraspecific competition plays a very important role in driving microevolution (i.e., such selection favors greater adaptation to the environment, broadly defined).
      2. That is, microevolution is a direct consequence of the extreme overlap between niches seen with conspecifics.
  7. Interspecific competition
    1. Lower than intraspecific competition:
      1. The degree to which niches overlap between species is, of course, less than that seen within species.
      2. Thus, intraspecific competition tend to be greater than interspecific competition.
      3. Nevertheless, interspecific competition which results from niche overlap is often greatest, not surprisingly, between similar organisms which obtain similar food (and other resourses) in similar ways from similar sources.
    2. Should niches nevertheless significantly overlap, evolution can tend toward either the elimination of one or the other species through competitive exclusion.
    3. Drives niche expansion:
      1. Interspecific competition can lead to a divergence of niches coupled with a maintenance of both populations (i.e., no or delayed extinction).
      2. This divergence is called resource partitioning.
    4. Limits niche expansion:
      1. Interspecific competition can also limit niche expansion.
      2. That is, the potential for such niche expansion, though certainly driven by the presence of the other species, is limited, however, to the extent additional species already occupy niches into which a species may expand.
    5. Limits carrying capacity:
      1. By both reducing the size of an organisms realized niche, and by limiting niche expansion, interspecific competition serves as one factor which can affect (lower) carrying capacity.
      2. That is, realized niche and lowered carrying capacity due to interspecific competition are really the same thing.
  8. Coevolution
    1. Evolving in concert:
      1. When one species responds evolutionarily to another species (and vice versa), with neither species driven to extinction, coevolution is said to occur.
      2. For example, one competitor may specifically evolve in response to a trait associated with a second species, and that trait may in turn evolve in response to the evolution by the first species.
    2. Interspecific competition can lead to coevolution.
    3. Example: predator-prey interactions
      1. Predator-prey species pairs often undergo arms races whereby the prey become better over time at eluding the predator (those prey better able to elude the predator show survival biased in their favor).
      2. Those predators best at overcoming a prey's defenses, in turn, more efficiently exploit the prey (those predators more capable of obtaining food may display a fitness advantage over less able conspecifics).
    4. Product of interspecific cooperation
      1. Coevolution need not be a consequence solely of competition between species.
      2. For example, the endosymbiotic mitochondria and chloroplasts, along with their ecuaryotic host organisms, are examples of products of coevolution toward increased (and, in this case, profound) cooperation.
  9. Symbiosis
    1. Spatially intimate, long lasting relationship:
      1. Symbiosis is a relationship between at least two individuals, usually of different species, which is both spatially intimate and long lasting (long, particularly, relative to generation times).
      2. Coevolution and symbiosis feedback upon one another.
      3. That is, usually symbiotic relationships are products of coevolution between the two species involved.
    2. Spectrum of harmful to helpful:
      1. Symbiotic relationships are classified in terms of the degree to which one or both of the individuals are affected, either positively or negatively, by the relationship.
      2. For example, symbiotic relationships with varyig degrees of cooperation or harm are called:
        1. commensalism
        2. mutualism
        3. parasitism
  10. Commensalism
    1. Helpful, not harmful:
      1. Commensalism is a symbiotic relationship in which one member is unharmed by the relationship and the other member derives a net benefit from the relationship.
      2. Proof that both species either are or are not deriving benefit from a symbiotic relationship often makes it difficult to definitively state that any given relationship is an example of commensalism rather than mutualism.
    2. Clownfish living among the stinging tentacles of sea anemones gain protection as well as a food source.
    3. Birds nesting in a tree. The tree is effectively not affected while the bird benefits in having a place to nest.
    4. Example: clownfish and anenomes:
      1. Organisms attached to larger, mobile organisms. The smaller organisms, such as barnacles found on whales, benefit by having a place to live as well as a potential for increased gamete or progeny dispersion.
      2. In addition, such organisms can benefit from the increased flow of nutrient filled water past them or even from being essentially on site to access any food not fully utilized by their host organism.
  11. Mutualism
    1. A symbiotic relationship in which both members derive a net benefit from the relationship.
    2. The ancestors of mitochondria and chloroplasts benefited from the food supply and increased mobility available to them in their eucaryotic cell hosts while simultaneously supplying those hosts with the benefits of aerobic respiration and photosynthesis.
    3. Example: microbial antagonism:
      1. Microbial antagonism is the tendency of the normal microbial flora found on an individual to not cause disease but nevertheless to occupy a niche which precludes the ability of disease causing microorganisms from gaining a toe hold on the host.
      2. Often microbial antagonism results simply from the normal flora occupying space which otherwise might be available to disease causing organisms, or by the normal flora actively modifying their living area in such a way that growth by disease-causing microorganisms is precluded.
      3. Here the flora benefit by having a place to live and secretions to live on while the host benefits from a lower incidence of disease.
    4. The Rhizobium-legume root nodule relationship is a mutual one since the former gains protection, nutrients, and an otherwise appropriate environment in which to live while the plant benefits from nitrogen fixing.
    5. The flowering plant-flying penis pollinator (insects, birds, and bats) is an example of mutualism because while the flowers supply nutrients to the various flying penises, the flying penises pollinate the plants (hence their highly descriptive name).
  12. Parasitism [parasite]
    1. Parasitism is a symbiotic association between one organism (the parasite) and a second organism (the host) in which the parasite derives benefits and the host is injured in some way.
    2. Smaller than host:
      1. Usually a parasite is considered to be something smaller than the host and therefore capable of parasitizing only one host at a time, often no more than one host per generation.
      2. Otherwise, the parasite-host relationship resembles that of the predator-prey relationship.
    3. Many (though not all) disease causing microorganism (as well as various worms) are essentially parasites, living within their host, drawing benefit from living there, and obviously harming their host in the process (disease is considered, by definition, to be something that harms the host).
    4. Example: intracellular parasitism:
      1. A number of bacteria as well as all viruses intracellularly parasitize individual cells, gaining nutrients and, in the case of viruses, metabolism, often at the expense of the life of the infected cell.
      2. Such symbiotic relationships resemble parasitism more than predation especially when the cell is not entirely (or rapidly) crippled by the relationship.
  13. Predator
    1. Consumer:
      1. A predator is a species which consumes members of another species.
      2. That is, a consumer.
    2. More than one prey organism:
      1. Usually one distinguishes predators from parasites in terms of whether the non-host lives in or on a sole individual member of the prey species that it consumes.
      2. Usually this implies that predators are usually relatively large (though not necessarily larger) when compared with prey species.
      3. Also, predators tend to consume more than one prey individual in the course of the predators life span.
  14. Predatory-prey interactions
    1. Interspecific competition w/o niche overlap:
      1. Predator-prey interactions interactions are a second means by which interspecific competition may be achieved is through various inter-trophic interactions.
      2. Such interspecific competition does not result from niche overlap (beyond habitat overlap) but nevertheless can obviously play a significant role in the evolution of species.
    2. Predators help define prey species realized niche:
      1. The presence of predators is a means by which prey numbers may be reduced to levels less than the predator-less carrying capacity of an ecosystem (i.e., reduced realized niche).
      2. Removal of predator species can thus lead to rapid population growth of prey species resulting in marked environmental change.
    3. Example: modern medicine:
      1. The most significant such example occurred with the eradication of much human disease and premature death through improved sanitation and vaccination (the culling of parasites).
      2. This allowed humans to enter an all but unchecked exponential phase of growth resulting in the unprecedented environmental degradation we observe today.
      3. That is, only with the eradication of much of human microbial disease have humans been able to approach the current human carrying capacity of our entire planet.
    4. Role of environmental complexity:
      1. The extremes to which predator-prey interactions may drive populations are dependent in a large part on the complexity of the environmental context in which they occur.
      2. The range of ecosystem complexities which can affect predator-prey interactions include:
        1. simple ecosystems
        2. existence of prey sanctuaries
        3. greater than one prey species
        4. complex ecosystems
    5. Simple ecosystems:
      1. Simple ecosystems may be defined as ones which:
        1. are very simple
        2. are completely homogenous (well mixed)
        3. contain only a single prey species which is easily exploited
        4. contain only a single predator species
      2. In such simple ecosystems the predator species tends to be able to drive the prey species to extinction, and then go extinct itself.
    6. Prey sanctuaries:
      1. A different result occurs in an ecosystem in which not all prey individuals are susceptible to the predator species (i.e., the predator is incapable of driving the prey to extinction perhaps due to the existence of some sanctuary).
      2. In such an ecosystem, to the extent the predator is capable, given sufficient numbers, of drastically reducing the prey species population, the predator and prey population sizes will oscillate.
      3. That is, large numbers of predators will drive the prey to low numbers. The resulting relative dearth of prey will precipitate a dramatic decline in predator numbers. The subsequent relative dearth of predators, in turn, allows the prey to reestablish themselves. Of course, when prey numbers become sufficiently high, this will lead to a rebounding of predator numbers, ultimately resulting in another round of decimation of the prey species. And so on.
    7. More than one prey species:
      1. In more complex communities consisting of more than one prey species, each of which are not completely susceptible to extinction through predation, the relative abundance of each prey species will be regulated by the predator.
      2. The predator will tend to subsist more on the more abundant, easier to exploit (and otherwise more desirable) prey species, then the less abundant, harder to exploit (or less desirable) prey species. Exploitation can reduce the size of individual prey species populations, but low population size can also reduce the absolute rate of exploitation. Consequently, the relative abundance of all prey species will tend to balance out, each at some relative exploitation difficulty/number balance.
      3. In terms of coevolution, there tends to evolve a balance between number, ease of acquisition, prey desirability, and a tendency toward predator and prey specialization, e.g., very high acquisition efficiency. When only a single prey species is avaiable, one would expect an evolution toward a higher efficiency of acquisition of that prey species than if resources are devoted to the acquisition of more than one prey species.
    8. In sufficiently complex ecosystem predator numbers may be limited by some parameter other than solely prey number, thus allowing an avoidance of predator-prey oscillations.
  15. Plant defenses
    1. Co-evolutionary relationship:
      1. Plant defenses represent the products of important co-evolutionary relationships between plants and the consumers of plants.
      2. Knowledge of plant defenses is important both from the point of view of understanding the power of co-evolutionary processes, ad because these adaptations play enormous roles in defining the dynamics of ecosystems.
    2. Categories of defenses:
      1. Plant defenses may be divided into various categories including:
        1. morphological defenses
        2. secondary chemical defenses
        3. inducible secondary chemical defenses
        4. nutritional inadequacies
    3. One argument for why large brains in primates evolved is that large brains (relative to body size) are a co-evolutionary response plant defenses. That is, smart monkeys are better at finding and utilizing plant products lacking in strong defenses than are less intelligent monkeys.
  16. Morphological defenses
    1. Size:
      1. Morphological defenses range from those applicable to herbivores only of certain scales to those generalizable to herbivores of many sizes.
      2. For example,while thorns may be adequate defenses against predation by larger mammals, plant hairs serve a similar purpose against insects.
      3. Alternatively, certain parts of plants (or the whole plant) may be encased in a tough housing or otherwise be difficult to chew through. Examples include such things as:
        1. the shell of a nut which protects the plant embryo
        2. the silica deposited in the leaves of grasses
      4. Both of these require specialized teeth (or equivalents) to exploit efficiently.
  17. Secondary chemical defenses
    1. Chemical warfare:
      1. Plants are the true masters of chemical warfare.
      2. Plants produce a vast number of chemical compounds not required for their metabolism.
      3. These so-called secondary chemicals exist, apparently, for the sole purpose of poisoning consuming herbivores.
    2. Often species specific defenses:
      1. Many of these secondary chemicals, however, are often specific in the species they affect.
      2. If this were not so, then many (most, all?) plants which humans use as food products would be unfit to eat. Instead, such plants may be unfit to eat by some insect predators, but not the evolutionarily less destructive human predators.
    3. Often otherwise useful:
      1. An important byproduct of many secondary chemicals is bioactivity in humans.
      2. That is, though a given plant may be poisonous to eat, that plant perhaps for this very reason may nevertheless yield pharmaceutically important chemicals: poisons by definition exhibit bioactivity and careful control of dosage and delivery can result in powerful pharmacological effects.
      3. Yet another reason for not destroying all of earth's creatures is that the world's threatened plants represent an enormous reservoir of bioactive chemicals which may be lost to man forever upon their extinction.
      4. Caffeine and nicotine are both secondary metabolites that likely play protective roles.
    4. Often carcinogenic:
      1. Another important aspect of secondary chemicals is that many of them function in such a way that they are potential carcinogens.
      2. Bruce Ames, a noted toxicologist, in fact argues that the carcinogens found in ordinary plants far exceed the carcinogens artificially added to foods (for example, pesticides).
      3. However, before you throw out that broccoli in favor of a burnt hunk of steer, note that plants also contain many chemicals that act to neutralize the carcinogenicity of secondary chemicals. Presumably as a consequence, a high intake of plant products is actually associated with a substantially lowered susceptibility to various cancers.
      4. Want to live as long as you can? Eat plenty of fresh plant products, especially large varieties of fresh vegetables, and only low quantities of fat, especially animal fats (oh yes, and don't smoke, avoid recreational drug use, exercise regularly, keep your weight down, drink only in moderation, wear a seat belt, and don't own a gun).
  18. Inducible secondary chemical defenses
    1. Avoidance of self-poisoning:
      1. For plants, evolution of secondary metabolic poisons might require evolution of compensating tolerance for these poisons in the plant.
      2. One way to accomplish this is via compartmentalization of secondary metabolites.
      3. For example, not all secondary chemical defenses associated with plants are found at all times in all parts of plants.
    2. Synthesis only upon predation
      1. In fact, many plants are able to synthesize various secondary chemical defenses only upon injury associated with predation, and then only locally.
      2. Such strategies allows the plant to utilize poisons to which they themselves may not be resistant, as well as to deliver higher concentrations of these chemicals to the site where they might do the most good than otherwise would be available if these chemicals were produced in advance then stored throughout the plant.
  19. Nutritional inadequacy
    1. Cellulose content:
      1. Plant parts containing high ratios of cellulose to vitamins, proteins, and other nutrients are not as desirable as those containing lower amounts of cellulose relative to nutrient content (particularly if cellulose may not be efficiently exploited as a food source by a given herbivore).
      2. Nutrient rich plants are more likely exploited than nutrient poor plants, resulting in a selective advantage accrued by the latter.
    2. Low concentration of key nutrient:
      1. Plants can limit specialization to their exploitation by maintaining only very small stores of key nutrients, such as certain amino acids (e.g., reducing the relative use of certain amino acids, especially typically essential amino acids in their proteins).
      2. This forces herbivores to concentrate their exploitations on more than one plant species thus reducing the potential for their co-evolution of greater efficiencies of predation on nutritionally inadequate plant species.
  20. Herbivore co-evolutionary responses to plant defenses
    1. For herbivores, an upside of plant defenses is that to the extent a defense may be overcome, that herbivore may gain exclusive or near exclusive exploitation of that plant.
    2. Reduced long-term fitness:
      1. Overcoming plant defenses may require sufficient specialization that the survival of the herbivore becomes intimately tied to the survival of one or only a few plant species.
      2. This could set up the herbivore for extinction given environmental changes which reduce the population sizes of the plant species it consumes.
  21. Animal defenses
    1. Those of plants and then some:
      1. Like plants, animals found at lower trophic levels (plants, of course, are found at the lowest) are often under strong selective pressure to avoid being eaten.
      2. All of the following act to increase the likelihood of survival of individuals animals faced with predation:
        1. moving faster than predators
        2. moving more nimbly than predators
        3. hiding from predators
        4. attacking predators in some manner
        5. being or to be sufficiently well armored (with hard things, sharp things, are stinging things) that predators find it difficult to eat an animal even if that animal is successfully caught
        6. being inedible
    2. Benefits of being inedible:
      1. Becoming lunch does nothing for personal survival, even if it is the prey that has the last laugh in, for example, making the predator sick.
      2. This contrasts with many plants which often are capable of survival past predation, and therefore can allow various forms of inedibility to deter future herbivore attack.
      3. However, a predator capable of learning may be capable of associating the occurrence of getting sick or lack of a tasty morsel with the appearance of a given kind of prey. It is to that predator's benefit to no longer expend energy catching such prey, even if the predator succeeded in killing the prey which was caught.
      4. This recollection benefits conspecifics.
      5. To the extent closely related conspecifics benefit more than distantly related conspecifics (i.e., those with greater odds of carrying the allele associated with upsetting the predator), such a strategy will, perhaps counterintuitively, increase the fitness associated with the organism which is eaten (by reducing the odds that close relatives are eaten).
      6. This situation actually is completely analogous to that seen with partially predated plants, except with these plants there is much greater linkage between the future survival of an allele and the expression of that allele since this occurs within the same individual.
  22. Warning [aposematic] coloration
    1. Advertising inedibility:
      1. Animals which produce defenses that act to deter predation, whether those defenses act passively (i.e., only upon being eaten) or actively (the potential prey attacks the predator), very often display bright coloration.
      2. This coloration serves as a primary line of defense against predation.
      3. That is, predators who have had bad experiences with bright, specifically colored prey will tend to avoid predating such prey in the future.
    2. Note, however, that this strategy consequently has an associated density dependence; only so long as a species is sufficiently common that a predator will likely come into contact with a member at least twice in a life time will the strategy display any effectiveness.
    3. The black and yellows striping found on bees and other stinging insects.
    4. The black and red coloration sported by the poisonous (should they be eaten) Monarch butterflies.
  23. Batesian mimicry
    1. Faking bad taste:
      1. As they say, all successful systems breed parasites.
      2. Interestingly enough, bad tasting prey can be so successful in convincing predators not to eat their kind that other, good tasting species can avoid predation simply by having an appearance which is similar to that of bad tasting species.\
      3. This kind of fakery is termed Batesian mimicry.
    2. Density dependence:
      1. Given a species which resembles a second aposematically colored species. If the second species possesses an effective defense against predation, the first, mimicking species will be similarly protected so long as a predator has had previous experience with the second species and mistakes the first for the second. This strategy is called Batesian mimicry.
      2. Tidy as this strategy at first may seem, there are limitations to it.
      3. Particularly, the greater the fraction of similar looking organisms which taste good, the less overall the advantage associated with looking like a bad tasting organism.
      4. Consequently, the fitness advantage associated with this kind of mimicry is frequency dependent (frequency of the good tasting mimics within the overall population of similar looking organisms).
      5. In particular, this requirement for the predator to learn to associate the look with the effective defense demands that the frequency of the mimic be low relative to that of the species being mimicked. Otherwise, neither the mimic nor the mimicked will be able to effectively use their aposematic coloration.
    3. Example: butterflies:
      1. The classic examples of Batesian mimicry are those found among good and bad tasting butterflies. Butterflies are often victims of visually locating predators.
      2. Consequently, their Batesian mimicry is more accessible to humans (with our large visual bias) than are other systems.
      3. This, particularly, is why humans managed to pick up on this kind of Batesian mimicry.
    4. More than skin deep:
      1. Note that mimicry is not limited to coloration.
      2. Any means by which a potential prey species can increase its resemblance to a prey species possessing an effective defense against predation (behavior, smell, etc.), especially from the point of view of the predator, will essentially receive some of the benefits associated with that defense without actually evolving a specific defense.
  24. Muellerian mimicry
    1. Cooperative bad taste, etc.:
      1. If two species both possess effective defenses and also have similar aposematic coloration, the total density for the given aposematic coloration is larger than it would be if each species stuck to a distinct and different color pattern.
      2. The greater the density of similarly colored species with effective defenses, the more likely a predator will come into contact with a member of this system at least twice in its life time and therefore the more effective the system of aposematic coloration is in protecting all of its members.
      3. Similar coloration like this is called Muellerian mimicry.
    2. The alternating black and yellow stripe motif sported by a large variety of stinging insects (bees) is an example of Muellerian mimicry.
  25. Cryptic coloration [camouflage]
    1. Hiding in front of something:
      1. Cryptic coloration is essentially the opposite of aposematic coloration.
      2. Animals lacking in effective defenses are best off avoiding confrontation with predators all together.
      3. One route to such avoidance is to avoid being seen.
      4. Cryptic coloration achieves this by rendering the bearer difficult to see against a certain background.
      5. Hunters achieve a similar state of being by wearing appropriate colored camouflage clothing.
      6. example: peppered moths
  26. Vocabulary
    1. Actual niche
    2. Animal defenses
    3. Aposematic coloration
    4. Batesian mimicry
    5. Coevolution
    6. Commensalism
    7. Competitive exclusion
    8. Cryptic coloration
    9. Fundamental niche
    10. Herbivore-plant coevolution
    11. Inducible secondary chemical defenses
    12. Interspecific competition
    13. Intraspecific competition
    14. Morphological defenses
    15. Muellerian mimicry
    16. Mutualism
    17. Niche
    18. Nutritional inadequacy
    19. Parasitism
    20. Plant defenses
    21. Predator
    22. Predator-prey interactions
    23. Realized niche
    24. Secondary chemical defenses
    25. Symbiosis
    26. Theoretical niche
    27. Warning coloration
  27. Practice questions
    1. The full spectrum of resources potentially available to an organism is called its ___________. [PEEK]
    2. Clownfish living among the stinging tentacles of sea anemones gain protection as well as a food source. The sea anemone neither gains nor loses from this symbiotic relationship which therefore is considered to be an example of _________. (choose best answer) [PEEK]
      1. commensalism
      2. mutualism
      3. parasitism
      4. predation
      5. all of the above
      6. none of the above
    3. In very simple ecosystems (two species only, predators kill prey in order to obtain nourishment, completely homogeneous environment, no prey refuges) predator-prey interactions tend to lead to ____________. [PEEK]
    4. Employing ____________ secondary chemical defences allows plants to utilize poisons which they themselves may not be resistant to, as well as to deliver higher concentrations of these chemicals to the site where they might do the most good, and than otherwise would be available if these chemicals were produced in advance then stored throughout the plant. [PEEK]
  28. Practice question answers
    1. fundamental or theoretical niche
    2. i, commensalism
    3. extinction
    4. inducible
  29. References
    1. Postlethwait, J.H., Hopson, J.L. (1995). The Nature of Life. Third Edition. McGraw Hill, Inc., New York. pp. 841, 850-862.
    2. Raven, P.H., Johnson, G.B. (1995). Biology (updated version). Third Edition. Wm. C. Brown publishers, Dubuque, Iowa. pp. 460-485.