Community Interactions

Community – all the species in a given location at a given time Habitat the physical environment they live in : Redwood forest Niche – how a species uses the resources in its habitat –Builds nest in tree top vs. lower branches Similar species coexist by Niche specialization.

Paramecium caudatum Paramecium aurelia Competitive exclusion

Competitive Exclusion The more similar two species’ niches the more they compete. No two species can share the exact same niche- one dies out. Species evolve to diverge their niches by Resource Partitioning

Competition for space on the rocks Weak competitors stuck higher up in the intertidal

Resource Partitioning

Smartweed Indian mallow Bristly foxtail

Character Displacement Two species with same Beak size can not Coexist on same island One adaptive result of resource partitioning

Types of Interspecific Interactions Species ASpecies B Commensalism+0 Mutualism++ Competition-- Predation+- Parasitism+-

Canadian lynx (dashed line) Snowshoe hares (solid line) Predator & Prey a Mutualism?

Caulerpa taxifolia suffocating a marine ecosystem Do not post on Internet

Number of species of antsNumber of species of breeding birds

Mosses Vascular Plants Number of colonizing species of mosses and vascular plants recorded on Surtsey between 1965 and 1973

Keystone species Pisaster (Sea Star) defends tide pool from being taken over by mussels, barnacles.

Sea Otters maintain Kelp forest Otters are a Keystone species Kelp are the base of the kelp forest community Urchins eat kelp at their base Otters eat urchins, keeping their numbers low. Otter numbers along California are dropping. Alaska- Orcas starting to eat otters, because seal numbers are dropping No fish for seals

Succession:Community Structure changes over time Primary Succession: starts with no soil, just bare exposed rock –Progresses in stages until long term climax stage Secondary Succession starts with the climax vegetation type –Disturbance (fire) resets timeline –Progresses in stages back to climax.

1-Glacier Retreats 2-Barren Rock 3-Moss and Lichen

4-Cottonwood and Alders 5-Spruce moves in 6-Spruce and Hemlock Climax Vegetation

Fire Cycle in Chaparral

Fire poppies in burn area

Madrones sprouts from burl

Ceanothus seedlings sprout after fire

1 month post fire Schmidts, M.J., D.A. Sims, J.A. Gamon California State University, Los Angeles, CA

First spring 3 years post fire

20 and 40 years post fire

Mosaic of ages burns