Section 2 – Species Interactions

The Niche and Competition An organism’s niche is affected by both its tolerance and competitive interactions Habitat: general place it lives Niche: an organism’s habitat, resource use, and fundamental role in a community Habitat Food Source How/When it Reproduces Interactions with other Organisms

Tolerance Tolerance: the ability to survive and reproduce under changing environmental conditions Specialists: very restricted tolerance ranges Ex. Panda Bears Generalists: wide tolerance ranges Ex. Rats BOTH may not be able to adapt when conditions change.

Competition Multiple organisms seek the same limited resource. Food, Light, Water, Space Direct Competition: physically, for territory Indirect Competition: flowers, for pollinators Intraspecific Competition: competitive interactions among members of the same species Interspecific Competition: competitive interactions among members of two or more different species

Competitive Exclusion Competitive Exclusion: if one species is a very effective competitor, it may exclude another species from resource use entirely Mussel and Clam Populations in Lake St. Clair Lake St. Clair connects Lake Erie and Huron 20 native mussel species By 1997, they were all gone When Zebra Mussels attack, shellfish cannot open their shells – they eventually suffocate or starve

Fundamental and Realized Niche Usually, neither competing species fully excludes the other. Instead, competing species tend to adjust to each other, minimizing competition. Changing Behavior Using only a portion of the resources they are capable of using Fundamental Niche: full niche of a species Realized Niche: a niche restricted by competition

Resource Partitioning Resource Partitioning: a process that allows different species to share common resources If 2 bird species eat the same type of seeds 1 specializes in eating larger seeds 1 specializes in eating smaller seeds OR 1 is active in the morning 1 is active in the evening

Character Displacement Character Displacement: resource partitioning can lead to the evolution of physical characteristics among the competing species that reflect their specialized role in the environment Darwin’s Finches – Galapagos Islands Birds specialize in eating small seeds = small bills Birds specialize in eating large seeds = large bills

Predation, Parasitism, and Herbivory “0” = relationship in which there is no effect, or the effect is neutral “-/-” = negative effect on both organisms Competition “+/-” = beneficial for one participant, but harmful to the other Predation Parasitism Herbivory

Predation and Population Cycles Predation: the process by which individuals of one species (the predators) hunt, capture, and feed on individuals of another species (the prey) Population Cycles INCREASE in Prey Population INCREASE in Predator Population DECREASE in Prey Population DECREASE in Predator Population and Repeat

Predation and Evolution Natural Selection – evolution of better predators Predators skilled at capturing prey – more successful Prey – evolution of Defense Mechanisms Strong selective pressure – IMMEDIATE DEATH

Coevolution and Evolutionary “Arms Race” Coevolution: the process by which two species evolve in response to changes in each other Newt develops toxins that kills predators In response, predators evolve immunity to the toxins In response, newt evolve stronger toxins Arms Race: each species develops stronger and stronger “weapons” in response to the other ALL SPECIES ADAPT TO BETTER SURVIVE AND REPRODUCE IN THEIR ENVIRONMENT.

Parasitism Parasitism: a relationship between two organisms from different species in which one organism (the parasite) depends on the other (the host) for nourishment or some other benefit Tapeworms Ticks Symbiosis: a long term and physically close relationship between two organisms from different species in which at least one organism benefits Commensalism Mutualism Parasitism

Herbivory Herbivory: the act of feeding on a plant Insects – most common type of herbivore Hervibory usually doesn’t kill the plant Affects growth and population Natural Selection has given plants defenses: Produce Toxic/Distasteful Chemicals Thorns, Spines or Irritating Hairs In response, herbivores evolve ways to overcome.

Mutualism Mutualism: (+/+) a relationship between two organisms from different species in which both organisms benefit Plant Roots + Fungi = Mycorrhizae Plant provides energy, fungus assists in nutrient absorption Pollination Pollinators enable sexual reproduction in plants Pollinators receive nectar as a reward

Commensalism Commensalism: (+/0) a relationship between two organisms from different species in which one benefits and the other is unaffected Example: Palo Verde trees in the Sonoran Desert Trees create shade and leaf litter that allow the soil to hold moisture Soil becomes cooler with more moisture, making it easier for young plants to germinate and grow Other desert plants grow beneath the “nurse” tree

Section 3

Section 4