community interactions. community – all the species in a given location at a given time habitat...

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

Bristlyfoxtail

CharacterDisplacement

Two species with same Beak size can notCoexist on same island

One adaptive result of resource partitioning

Types of Interspecific Interactions

Species A Species B

Commensalism + 0

Mutualism + +

Competition - -

Predation + -

Parasitism + -

Canadian lynx (dashed line) Snowshoe hares (solid line)

Predator & Preya Mutualism?

Caulerpa taxifolia suffocating a marine ecosystem

Do not post on Internet

Number of species of ants Number 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 HemlockClimax 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

http://vcsars.calstatela.edu/eas_00/miriam/miriam_esa_00.html

First spring 3 years post fire

20 and 40 years post fire

Mosaic of ages burns