Species Interactions 11/10 & 11/12

Intra-specific Interactions

interactions between individuals of the same species 

Inter-specific Interactions

interactions between individuals of different species

Example of Intra-specific interactions: intraspecific competition

individuals of the same species/population competing for limited resources (space, mates, territory, dominance, food)

Example of Inter-specific interactions: inter-specific competition

individuals of different species competing for the same resources.

Niche Definitions

• "the range of resources and conditions allowing the species to maintain a viable population";

• "the interrelationship of a species with all the biotic and abiotic factors affecting it";

• "defines an organism's role within an ecosystem: its food, shelter, and its behavioral role"

What is competitive exclusion also known as the limiting similarity principle? 

Two species with identical niches cannot coexist. One is a stronger competitor and drives the weaker competitor to a lower growth rate and sometimes to extinction. 

Paramecium experiments

Fundamental Niche

the complete set of conditions under which an organism could potentially survive and reproduce (SimBio); The abiotic conditions required for a species to persist.

Realized Niche

is the subset of the fundamental niche describing the conditions under which an organism actually lives, given limitations created by biotic interactions with other species.

Barnacle experiments

What factors promote coexistence?

• Use of resources differs. Niches do NOT completely overlap! (niche/resource partitioning)

• Predator-prey dynamics

• Intra-specific competition

• Habitat heterogeneity (variation in environmental conditions and resources within a habitat)

Niche/Habitat Partitioning

Species living together use slightly different resources enabling them to coexist in a community. Habitat partitioning is a case of niche partitioning specially from spatial separation within the habitat.

Character displacement

Competition drives populations of two species living in the same area to evolve different traits!

Predation (+/-): What enables stable coexistence of predators and prey?

Predator effect on prey populations could be minor if:

• Predator densities are low

  • Predators have territories that enforce low density

• Predators mainly take prey destined to die without reproducing anyway (old, infirm or very young)

• Prey switching – predators switch to new prey when the density of prey drops

What is the role of camouflage?

To avoid detection from predators or prey.

What is the role of aposematic coloration? 

a warning signal about prey defense to potential predators to advertise their toxicity, venom, or unpalatability.

Batesian Mimicry

A harmless, edible species (the mimic) evolves similarity to a harmful or unpalatable species (the model)

Mullerian Mimicry

Two (or more) distasteful or harmful species evolve to resemble each other (Monarch and Viceroy butterflies)

Herbivory

Predation on plants (consumption interaction, +/-)

How do plants defend themselves?

Physical Defenses: spines, fibers, hooks, stingers, wood, etc.

Chemical Defenses: Tannins, Nicotine, caffeine, opium, strychnine, digitalis, etc. (can be secondary defenses)

Consequences of defenses on plant

Can be costly to the plant. Plants must balance resources between defense with growth and survival (may grow slower, reproduce less often, or reproduce with fewer offspring)

How can herbivores take advantage of plant defenses for their own purposes?

• Detoxification: Evolving to metabolize plant toxins into harmless or even beneficial compounds.

• Sequestering: Storing plant chemicals in their own bodies to use for their own defense against predators.

Example of herbivores taking advantage of plant defenses

For example, milkweed plants can produce toxins to deter insect herbivores and produce trichomes (little tiny hairs). Milkweeds also produce latex. But monarch caterpillars, for example, have evolved immunity to the toxins of milkweed to be stored so they can use it as protection from parasites when they become butterflies.

Symbiosis

a close and/or long-term biological interaction, between two organisms of different species

Symbiosis: Mutualism

+/+, Species benefit other species because acting in their own self-interest happens to benefit others, not out of altruism.

Mutualism Example

Pollination as an example that sometimes despite mutual benefits, two partners have conflicting interests and individuals can try to take advantage.

Symbiosis: Commensalism

+/0, One benefits and one is not affected.

Commensalism Example

Ex: Tree frogs use plants as protection.

Symbiosis: Amensalism

-/0, One is negatively affected and one is not affected (very rare).

Amensalism Example

Ex: The broad canopy of a large tree blocks sunlight from reaching the forest floor, inhibiting the growth of smaller plants that need sunlight for photosynthesis.