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Interactions of SpeciesI. IntroductionA. Organisms Interrelate in Distinct Assemblages: Communities 1. Certain individuals are dominant in such collections a) Example: redwood trees in Oregon b) Community generally named after dominant species 2. Other organisms are characteristic as well a) Exist under conditions set by dominant species b) Niches of organisms overlap one another 3. Organisms in communities share historical dimension B. Similar Communities Stretch Over Vast Areas 1. Organisms within them interact in similar manners 2. Organisms follow set patterns of distribution 3. Coevolutin C. Organisms Change Relative to One Another Over Time 1. Flowering plants evolve in relation to pollinators 2. Pollinators, in turn, utilize flowers for food 3. Long-Term Mutual Evolutionary Adjustment of Features of One Group to Another II. Predator-Prey Interactions A. One Organism Is the Resource of Another 1. Commonly thought of in terms of animals hunting other animals 2. Plants also possess physical defenses and produce toxic chemicals 3. Animals also produce toxins and mimic other poisonous animals B. Plant Defenses 1. Attempts to limit being eaten by herbivores 2. Morphological defenses a) Thorns and spines limit activities of browsers b) Glandular hairs c) Deposition of silica toughens plant parts 3. Chemical defenses a) Restrict amino acids, thus limit nutritional suitability b) Produce secondary chemical compounds (1) Distinguish from primary chemical compounds (2) Primary compounds normally formed in metabolic pathways (3) Secondary compounds not formed in metabolic pathways c) Examples (1) Mustard family produces mustard oils (2) Potato/tomato family rich in alkaloids and steroids (3) Milkweed/dogbane families produce milky sap containing cardiac glycosides (4) Poison ivy group produces urushiol d) Chemicals are toxic, or disturb herbivore metabolism and/or development C. The Evolution of Herbivores 1. Some feed on restricted group of plants a) Group frequently produces secondary compounds (1) Example: cabbage butterflies (2) Example: monarch butterflies and milkweed (3) Example: amphipods feed on algae 2. Evolution of plant/herbivore interaction a) Plant evolves secondary compound b) Not eaten by herbivores, outcompetes others in area c) Herbivores evolve ability to break down compounds d) Herbivores lack competition from other herbivores e) Both plant and herbivore flourish D. Chemical Defenses in Animals 1. Frequently based on plant secondary compounds 2. Animals store rather than break down compounds a) Example: monarch butterflies b) Example: other milkweed herbivores 3. Such poisonous animals are generally brightly colored a) Warning coloration b) Advertise distastefulness to protect species 4. Nonpoisonous animals generally are not brightly colored a) Cryptic coloration b) Animals blend with habitat, thus hidden from predators 5. Poisonous animals may obtain defenses from other animals a) Nudibranchs eat hydroids with stinging cells b) Other nudibranchs eat poisonous algae 6. Many animals produce own poisonous chemicals E. Aposematic Coloration 1. Technical terminology for warning coloration 2. Characteristics of animals with extensive defenses a) Animals must occur at relatively high densities b) Generally live in family groups c) Camouflaged animals live singly 3. Selective advantage to animals with similar appearance F. Mimicry 1. Batesian mimicry a) Related but unprotected species resemble protected ones (1) Must be fewer in number than protected species (2) If in greater numbers, predators learn that most are edible b) Poisonous specimen is the model c) Nonpoisonous specimen is the mimic d) Example: viceroy butterfly 2. Muellerian mimicry a) Unrelated, but protected species resemble one another b) Strengthens the distastefulness and provides a group defense c) Examples include wasps and bees 3. Behavior is imitated in both types as well 4. Mimics must spend much time in model`s habitat III. Symbiosis A. Three Major Kinds of Relationships 1. Commensalism: one partner benefits, other neither benefits nor is harmed 2. Mutualism: both participants benefit 3. Parasitism: one partner benefits, other is harmed 4. Examples a) Lichens = alga + fungus b) Mycorrhizae = fungus + plant root c) Legumes = plant root + nitrogen-fixing bacteria d) Coral reef = complex system with numerous plants and animals e) Flowering plants + pollinators B. Commensalism 1. Individuals of one species physically attached to individuals of another species 2. Examples 3. Birds nesting in trees a) Epiphytic plants growing on other plants b) Barnacles attached to marine animals c) Sea anemones and clown fishes d) Certain birds clean parasites off grazing animals 4. Difficult to ascertain if second partner benefits or not 5. Gray boundary between commensalism and mutualism C. Mutualism 1. Example: leaf cutter ants a) Cut tropical leaves into pieces b) Inoculate pieces with specific fungus c) Fungi used as food by ants 2. Example: ants and aphids a) Aphids suck plant juices b) Ants protect and herd aphids like cattle c) Utilize aphid honeydew as food 3. Example: acacia tree and acacia ants a) Trees inhabited by ants produce food for them (1) Protein-rich Beltian bodies (2) Nectar at base of leaves b) Ants and larvae protected by thorns of tree c) Ants in return: (1) Attack all other herbivores (2) Cut away branches of competing plants (3) Wastes provide source of nitrogenous fertilizer D. Parasitism 1. Special form of symbiosis a) Parasite much smaller than prey b) Parasite in close association with prey 2. Some animal examples are readily identifiable, while others are not a) Vertebrates have animal or protist parasites b) Bacteria and viruses are not considered parasites though c) Lice are parasites, mosquitos are not 3. Some flowering plants are parasitic on other plants 4. Internal parasites more specialized than external ones a) More closely linked to host b) Morphology and behavior more greatly modified over time c) Bodily structure of parasite quite simplified Layout by J.T. Poirier © 2001 |