Community InteractionsChapter 53

Community Ecology

• Community – all the species in a given location at a given time

• Habitat the physical environment they live in, e.g. 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.

Fig. 32.8a

Fig. 32.8b

Energy Transfer in Ecosystems Food / Energy

PyramidPrimary Consumers eat producers,

incorporating the energy into the next level.

• Only 10 % of energy consumed moves to next level– Animals loose 90% of the energy at each level – Why are Big Fierce Animals so Rare??

• Consumers are Heterotrophs

Simple Food Chains

Trophic Levels

Both Marine and Terrestrial

Food Webs

• Energy transfer follows trophic levels

• Many animals eat at several trophic levels

• Omnivores: like most of us– At salad bar you’re a herbivore– Eating a burger makes you a carnivore

marsh hawk

crow

upland sandpiper

garter snake

frog

spiderweasel badger coyote

ground squirrelpocket gopherprairie vole

sparrow

earthworms, insects

First Trophic Level

Second Trophic Level

Higher Trophic Levels

Sampling of connections in a Tall grass prairie food web

grasses, composites

Plant Community structure

• Individualistic view (Gleason)

• Interactive view (Clements)• Whittaker’s test • Plant communities are loose

associations without discrete boundaries

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

Paramecium caudatum

Paramecium aurelia Competitive exclusion

Fig. 32.10

Follow up:

• Gause next added Paramecium aurelia with P. bursaria

• They used the resources differently and both survived at lower levels.

• Resource partitioning species evolve to avoid competition. – why?

Fig. 32.11

Resource Partitioning

Competition for space on the rocks

Weak competitors stuck higher up in the intertidal

Smartweed

Indian mallow

Bristlyfoxtail

• Nuthatch crawls down the tree’s bark eating insects

• Brown Creeper crawls up the same trees eating insects

Caulerpa taxifolia suffocating a marine ecosystem

• Introduced species often out compete natives

• Lack predators that the natives have coevolved with

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 + -

• Commensalism

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

Predator & Preya Mutualism?

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 community

• Urchins eat kelp • Otters eat urchins• Otter numbers along

California are dropping.• Alaska- Orcas starting to

eat otters, because seal numbers are dropping

• No fish for seals• Kelp forests disappearing

Species Richness• More energy available (productivity) the

species can exist.• The larger the community size the more

species can be supported.

Number of species of ants Number of species of breeding birds

Species Richness by Latitude

Island Biogeography Ideas:

• Size of island influences survival rate– Larger islands sustain more species

• Nearness to other island influences immigration rate– Near islands have more species than

distant islands

• “Islands” are any isolated habitat

Island Biogeography

• Larger islands sustain more species

Bio Reserve Model• Core - strict preserve, research. • Inner Buffer - hiking, Some

commercialization. • Outer buffer - (may not even be part of

park) camping, concessions, grazing timber, agriculture.–

Core

Fig. 23.26, p. 618

Core

• Round parks have less edge effect– Higher per cent

of park is in core area

Edge effect

• Natural vs. Artificial edges

Bio Reserve Model

• Corridors connect core areas from park to park forming land bridges

• Our national Forests serve this role in many areas of the west.

• Few Lager rounded parks, better than many smaller isolated parks fpr species richness

Biosphere Reserve

Core area

Inner Buffer

Outer Buffer

Fig. 23.27, p. 620

One Species

Three Species Overlap

Two Species Overlap

Existing Nature Reserves

Naalehu

Hilo

Kona

Fig. 23.28, p. 621

Succession: How the 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.

Cottonwood and Alders

Spruce moves in

Spruce and HemlockClimax Vegetation

Fire is a common disturbance in grasslands

Fire Cycle• Community most likely to burn in many areas.• Many homes now built in these areas.• Early succession after fire, nutrient limited, mostly

annuals and forbs (herbs) wildflowers.• Many species are sprouters-

– Burl survives fire, seeds out new shoots afterwards

• new growth may be very high in protein 14%, deer and other animals rely on this growth.

• some closed cone pines - need fire to release seeds.• Fire follower annual- seeds in soil seed bank

germinate and predominate first few years after fire• Shrub canopy closes in about 6 years

http://asd-www.larc.nasa.gov/biomass_burn/gifs/fla_ca/505.html

Fire poppies in burn area

Madrones sprout 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

Aposematic ColorationWarning I’m poisonous!

Batesian MimicryI only look dangerous

Mullerian MimicryWe both are dangerous

CamouflageI look like the background