Species Interactions: Comprehensive Notes

Species Interactions

Learning Objectives

  • Describe the different types of species interactions.
  • Explain coping mechanisms related to competition, predation, and coevolution.

Types of Species Interactions

  • Competition (-/-)
  • Predation (+/-)
  • Parasitism (+/-)
  • Mutualism (+/+)
  • Commensalism (+/0)
  • Amensalism (0/-)

Competition (-/-)

  • An interaction between organisms or species in which both require a resource that is in limited supply (food, water, territory).
  • Can be intraspecific (within the same species) or interspecific (between different species).
Darwin's Observation
  • "In looking at nature, never forget that every single organic being around us may be said to be striving to increase its number."
Types of Competition
  1. Exploitation
  2. Interference
Exploitative Competition
  • Consumption of resources by two species, where one species may limit resource availability to the other.
  • One species more efficiently uses a resource.
  • Example: Ants and rodents competing for seeds.
  • Exploitative competition also occurs among plants in the forest.
Interference Competition
  • Aggression between individuals of different species, fighting over the same resource.
  • Asymmetric: one species has an advantage over the other.
Allelopathy
  • A biological process where plants affect, often inhibitory, the growth and germination of other species within their space.
  • Production of compounds that inhibit the growth of other plants.
  • Chemicals released by one plant species negatively impact another.
    • Creosote bush (Larrea tridentata) is an important desert shrub found in the Great Basin, Mojave, Sonoran, and Chihuahuan deserts.
    • Salvia leucophylla (sage) in coastal sage scrub (California).
    • Centaurea maculosa (spotted knapweed) releases catechin into the soil, which, when absorbed by roots of other plant species, causes cell death, aiding invasiveness.
    • Paper mulberry (Broussonetia papyrifera) is an invasive shrub that releases phytotoxins concentrated in the soil's upper surface, inhibiting the growth of seedlings in many plants, such as conifers, by killing their germinating seeds.
    • Bracken fern (Pteridium aquilinum)
Methods of Obtaining Evidence of Competition
Tansley's Experiment
  • Experimental common garden with equal sun, rain, and temperature for each group of plants.
  • Galium saxatile grows best in acid, peaty soils, as observed in nature.
  • Galium sylvestre grows best in calcareous soils as observed in nature.
  • When the two are planted together:
    • G. sylvestre prevails on calcareous soil.
    • G. saxatile prevails on acid soil.
Connell's Experiment
  • Studied Chthamalus and Balanus barnacles in the intertidal zone.
  • Chthamalus realized niche is in the high tide area.
  • Balanus realized niche is in the low tide area.
Competition and Niches
  • Chthamalus fundamental niche includes the entire intertidal zone, but its realized niche is smaller due to competition with Balanus.
Diatom Experiment
  • Asterionella formosa (Af) and Synedra ulna (Su) compete for silica for the formation of cell walls.
  • Both grow well alone.
  • With insufficient silica, Su reduced the silica to a low level and drove Af to extinction.
Effects of Competition
Competitive Exclusion Principle (Gause's Law)
  • Strong competition can lead to competitive exclusion, local elimination of a competing species.
  • Illustrative graph showing the zone of overlap in food types eaten by Species A and Species B.
Competition Between Organisms of Different Species
  • Paramecium aurelia and Paramecium caudatum.
  • When grown separately, both species thrive.
  • When grown together, P. aurelia outcompetes P. caudatum, leading to the decline of P. caudatum.
Character Displacement
  • Evolution of anatomical differences that reduce competition between similar species.
  • Example: Geospiza fuliginosa and Geospiza fortis on Los Hermanos and Santa María, San Cristóbal islands.
  • Allopatric populations of G. fuliginosa and G. fortis have similar beak depths.
  • Sympatric populations on Daphne Island show character displacement in beak depths.
Definitions

  • Allopatric speciation occurs when a species separates into two separate groups that are isolated from one another.

  • Sympatric speciation occurs when there are no physical barriers preventing any members of a species from mating with another, and all members are in close proximity to one another.

  • Interspecific competition is a driving force for species to evolve adaptations for continued survival.

Strategies to Avoid Competition
  1. Resource partitioning: differentiation of ecological niches, enabling similar species to coexist in a community.
    • Example: Anolis lizard species demonstrate this strategy, with different species perching on different parts of the environment.
      • A. distichus perches on fence posts and other sunny surfaces.
      • A. insolitus usually perches on shady branches.
  2. Temporal partitioning: species use the same resources but at different times.
    • The common spiny mouse (Acomys cahirinus) and the golden spiny mouse (Acomys russatus) show temporal partitioning of their niches.
    • Both species are normally nocturnal.
    • Where they coexist, the golden spiny mouse becomes diurnal.
  3. Developing specialized niches
    • Through natural selection, different species of honeycreepers have evolved a specialized beak to take advantage of certain types of food resources.
      • Fruit and seed eaters: Greater Koa-finch, Kona Grosbeak
      • Insect and nectar eaters: Akiapolaau, Maui Parrotbill, Kuai Akialaoa, Amakihi, Crested Honeycreeper, Apapane
  4. Specialized Feeding Niches
    • Bristly foxtail (Setaria faberii), Indian mallow (Abutilon theophrasti), and Smartweed (Polygonum pensylvanicum) have different root depths.
    • Various bird species in a coastal wetland have specialized feeding niches.
      • Black skimmer seizes small fish at the water surface.
      • Brown pelican dives for fish.
      • Avocet sweeps bill through mud.
      • Dowitcher probes deeply into mud.
      • Herring gull is a scavenger.
      • Rudd turnstone searches under shells.
      • Flamingo feeds on minute organisms in mud.
      • Scaup and other diving ducks feed on mollusks.
      • Louisiana heron wades into water to seize small fish.
      • Oystercatcher feeds on shellfish.
      • Knot picks up worms and small crustaceans.
      • Piping plover feeds on insects and tiny crustaceans.

Predation (+/-)

  • An interaction where one species kills and eats the other.
  • Includes carnivory and herbivory.
Parasitoidism
  • An organism (generally insect parasitoid) predates on another insect called the host insect by laying eggs near or on the host insects.
  • These eggs hatch into larvae that feed on the tissues of the host insect and subsequently kill and eat it.
  • Has a life history intermediate between that of a predator and prey.
  • Consume nutrients and energy from the host.
  • Parasitic activities are limited to the larval stage.
  • Larvae consume the host either partially or completely.
  • Adult parasitoids are free-living and may be predaceous.
  • Confined to orders Hymenoptera and Diptera.
  • Examples: Spider host and wasp parasitoid, Tobacco hornworm larva loaded with pupae of the parasitoid Cotesia congregate.
Carnivory
  • Organism captures, kills, and consumes an animal.
Herbivory
  • Consumption of plant material by an animal.
Kinds of Herbivores
  • Grazers/folivores: Consume leafy materials.
  • Browsers: Eat mostly woody materials and bark.
  • Granivores: Consume plant seeds.
  • Frugivores: Consume fruit.
Predator Adaptations
  • Claws, teeth, fangs, stingers, and poison.
  • Search image.
  • Chemoreception.
  • Auditory sensation.
  • Echolocation system in whales.
Prey Adaptations
  • Speed
  • Crypticity.
  • Mimicry.
  • Camouflage.
  • Cryptic coloration: Canyon tree frog.
  • Aposematic coloration: Animals with effective chemical defense often exhibit bright warning coloration. Poison dart frog.
  • Batesian mimicry: A palatable or harmless species mimics an unpalatable or harmful model.
    • Hawkmoth larva mimics Green parrot snake.
  • Müllerian mimicry: Two unpalatable species mimic each other.
    • Cuckoo bee and Yellow jacket.
Herbivore Adaptations
  • Koala's GI tract is very long for its body size. It has a lengthy cecum where food is held to ensure as much nutrition extraction as possible.
  • Birds beak are of different shapes and sizes depending on their food source.
  • Herbivores have broad, flat molars (back teeth) with rough surfaces, used for grinding tough plant tissues.
Plant Adaptations to Herbivores
  • Secondary Compounds: Poisonous, irritating, or bad-tasting compounds synthesized by plants as a defense.

Coevolution

Predator and Prey Species Can Drive Each Other's Evolution

  • Intense natural selection pressures between predator and prey populations.
  • Coevolution: Cases where two (or more) species reciprocally affect each other’s evolution.
    • Example: A Langohrfledermaus bat hunting a moth.

Parasitism (+/-)

  • The parasite derives nourishment from another organism, its host, which is harmed in the process.
  • Ectoparasites: Live on the surface of the host.
  • Endoparasites: Live inside the host.
  • Examples: Tree with parasitic mistletoe, Trout with blood-sucking sea lampreys.
  • Songbirds are often heavily parasitized by ticks, leading to anemia and vulnerability to predation.
  • Fungal parasites often infect living organisms, such as plants, animals, or other fungi.
    • Shelf fungus releases enzymes to digest the wood of a tree, weakening it.
  • Examples of Endoparasites: Tapeworms, Roundworms, Viruses.
  • Roundworms: Elephantiasis is characterized by the thickening of the skin and underlying tissues, especially in the legs and genitals, due to blockage of the lymph nodes.
Parasite and Pathogen that Manipulate Host Behavior
  • Life Cycle of Plagiorhynchus cylindraceus, an intestinal parasite of birds.
  1. Adult female Plagiorhynchus lays eggs within the intestines of infected birds. The eggs are shed with feces.
  2. A terrestrial isopod eats the feces of an infected bird. The eggs of Plagiorhynchus hatch within a few hours; they develop into a mature larva in 60-65 days.
  3. The mature larvae of Plagiorhynchus alter isopod behavior; infected isopods leave sheltered areas and wander in the open.
  4. Leaving shelter makes the isopods more conspicuous and vulnerable to predation by birds. When eaten by a bird, the mature Plagiorhynchus attaches to the bird's intestinal wall.
A Plant Pathogen that Mimics Flower
  • The effects of fungus Puccinia monoica on morphology: a) a normally developed mustard plant, Arabis holboellii; b) a pseudoflower formed by A. holboellii infected by Puccinia.
Evolution of Parasites
  • Parasitism has stimulated the evolution of defenses in hosts.
    • Examples: Skin, openings such as eyes, mouth, and nose are defended with tears, saliva, and mucus. Parasites passing through these openings may be attacked by the immune system.
Adaptations of Parasites
  • Parasites adapt to efficiently exploit their host.
    • Examples: Tapeworms are so specialized that they have no digestive system; they live in the small intestine and absorb nutrients through the skin.

Mutualism (+/+)

  • Mutualistic symbiosis is an interaction that benefits both species.
    • Obligate: One species cannot survive without the other.
    • Facultative: Both species can survive alone.
  • Examples: Plant-coral, Mutualism-Mutualism.
Types of Mycorrhizal Fungi
  1. Arbuscular Mycorrhizal Fungi (AMF)
    • The fungus grows into the soil, extending some distance away from the root and penetrates into some of the plant root cells.
  2. Ectomycorrhizal Fungi (AMF)
    • The fungus forms a mantle around roots and a netlike structure around root cells.
  • Agropyron with mycorrhizal fungi maintained higher leaf water potential throughout a hot summer day.
  • Removing mycorrhizal hyphae reduces the rate of transpiration by red clover.
Ants and Swollen Thorn Acacia (Bullhorn)
  • Acacia tree and ants (genus Pseudomyrmex).
  • Area cleared by ants at the base of an acacia tree.
  • Growth and Survival of Bullhorn Trees With and Without Ants.
  • Pseudomyrmex survival rate with and without ants.
  • Plants with herbivorous insects (%) with and without ants.
Pollinators
  • Coevolution in a Flower and Its Pollinator: The very long mouth part of this hummingbird has coevolved with the tubular flower it pollinates.
Zooxanthellae in Coral Polyp
  • Waste (Carbon dioxide, Nitrate, phosphate) from coral is used by Zooxanthellae for Sugars, Photosynthesis, Amino Acids, and Lipids.

Commensalism (+/0)

  • One species benefits, and the other is neither harmed nor helped.
  • Enhances fitness of one species; no effect on fitness of the other species.
  • Examples: Barnacles attached to a whale.
  • Bromeliad roots on tree trunk without harming tree.
  • Lichens that grow on trees.

Amensalism (0/-)

  • An individual species harms another without obtaining benefit.
  • A nebulous relationship that involves chemical interactions such as allelopathy effect in plants and antibiosis.
  • Elephants stepping on ants or leveling brush does not benefit the elephant but causes harm.
  • Algal blooms can lead to the death of many species of fish and other animals, however, the algae do not benefit from the deaths of these individuals.
  • Penicillium releases Penicillin which kills bacteria without benefiting the bread mold.