Interactions Among Species Section 2.2

No two species occupy the same exact ecological niche. the role or “job” that an organism has in its ecosystem the organism’s way of life includes: habitat resource consumption interactions with other species ecological “services” provided – how it contributes to function and sustainability of the ecosystem No two species occupy the same exact ecological niche.

All of these factors together make up the big brown bat’s niche. Example: Big brown bat, Eptesicus fuscus Lifestyle: nocturnal Habitat: roosts in hollow trees, and man-made structures; hibernates in caves Range: North, Central, and South America Diet: insects Predators: cats, snakes, raccoons, owls Ecological Service: regulating insect populations All of these factors together make up the big brown bat’s niche.

Types of Species Interactions predation competition interspecific intraspecific symbiosis: mutualism parasitism commensalism Red billed oxpecker eats ticks on impala’s back (mutualism)

Predation occurs when one organism (the predator) feeds on another (the prey) Classify the lynx and hare in this photo as either predator or prey From the graph: What happens to the lynx population when the hare population increases?

Predator-Prey interactions influence the size of both populations. Bottom-Up Population Regulation fluctuation in a resource at the base of a food chain affects the animals at the higher trophic levels. Top-Down Population Regulation fluctuation in animals at higher trophic levels causes a change at lower trophic levels

Scenario Type of regulation DDT causes a decrease in hawk populations. Lizards, rabbits, and snake populations grow.   Abundant rainfall creates favourable growing conditions for grass. Populations of consumers grow. Rabbit birth rates are higher than normal. More grass gets eaten, but hawks also have more to eat.

Competition occurs when individuals compete with the same limited resource food, shelter, water, mates Two types: interspecific – Two different species compete intraspecific – Individuals of the same species compete

Observation: As population of female song sparrow grows, the number of eggs laid decreases. Hypothesis: Competition reduces the reproductive output (by limiting energy available for reproduction). Prediction: If birds are experimentally provided with food, no decrease in number of eggs laid will be observed. EXPERIMENTALLY-SUPPORTED

Making connections: Is competition a biotic or abiotic factor? Is competition density-dependent or independent? What type (interspecific vs. intraspecific) of competition was described in the previous example?

similar niche similar habitat similar diet similar lifestyle Competition can influence the niche an organism occupies. Organisms have to share available resources. Their realized niches are smaller than their potential niches. Example: Brook stickleback & Nine-spined stickleback similar habitat similar diet similar lifestyle similar niche

How does competition affect the habitat of brook sticklebacks? Scenario 1: Only brook sticklebacks present: The brook sticklebacks are found at all levels of the lake Scenario 2: Nine-spined sticklebacks also present: The brook sticklebacks are only found at bottom of the lake Competition for resources requires that the organisms share in order to co-exist in the same space.

Symbiosis Symbiosis is a type of interaction where members of two species live together in close physical association. can be further classified based on nature of interaction: mutualism parasitism commensalism

Mutualism both organisms benefit from the relationship Examples: Bees and flowers – Bees receive food (nectar), and flowers are pollinated. Gut bacteria and humans – Bacteria break down food molecules so that humans can absorb nutrients.

Parasitism one organism benefits while the other is harmed Examples: tapeworms in human intestines fleas live on animals http://www.youtube.com/watch?v=XuKjBIBBAL8

Commensalism one organism benefits, while the other is not affected in any way Example: Remora sharks use a special disk on their heads to attach to other animals, and “hitch rides” http://www.youtube.com/watch?v=9z3pqp12UEg

Homework Handout Pg. 64 #2, 5, 6, 7