Community Ecology I. Intro II. Community interactions A. What is a community? B. Questions II. Community interactions A. Types of interactions B. Which interactions structure communities? Ecobeaker demo III. Community Structure A. Measures of diversity B. Trophic structure IV. Control of community structure A. Dominant and keystone species B. Top-down vs. bottom-up C. Disturbance and succession D. Biogeography Community Ecology Reading: Chap. 53 As humans have altered ecosystems and caused species extinctions world-wide, a critical question is the extent to which such biotic modifications influence ecosystem-level processes.

I.A.What is a community? Definition: Any assemblage of populations in an area or habitat, i.e., all the different species interacting in a given location Encompasses many populations of different species.

What is a community? Individualistic or Interactive? Fig. 53.1

Questions How do biotic interactions affect the distribution of particular species? What biotic interactions structure communities? What factors cause changes in species richness across community types?

California Serpentine Grassland

Questions Important applications: Effects of invasive species? Fig. 55.7 Caulerpa Argentine ants Brown tree snake Nile perch

Questions Important applications: Effects of biodiversity loss on ecosystem functioning?

Responses of Productivity to Changing Plant Diversity Tilman et al. 1996 Hector et al. 2001 A number of experiments debate about both pattern and mechanism particularly, degree of comp vs. sampling effect define yr) Hooper and Vitousek 1997 Figure from Inchausti 2001

II. Interactions in communities A. Types of interactions Competition: -/- Predation: +/- Mutualism: +/+ Commensalism: +/0

1. Competition (-/-) Multiple organisms or species trying to maximize their own use of a limited pool of resources.

Competition Intraspecific Interspecific - among individuals of one species - implicit in the logistic population growth curve (density dependence) Interspecific - among individuals of different species - may restrict the range of one or the other species

Competitive exclusion and the niche Gause: Competitive exclusion principle. Ricklefs Fig. 19.6

Competitive exclusion and the niche Ecological niche: total of species abiotic and biotic resource use. - Two components: 1) what it needs to live (abiotic conditions, resources) 2) what it does - Niches can’t overlap exactly or species can’t coexist (i.e., need resource partitioning). - Tough to prove!

Intraspecific competition and niches And NUH is the letter I use to spell Nutches Who live in small caves, known as Niches, for hutches. These Nutches have troubles, the biggest of which is The fact that there are many more Nutches than Niches. Each Nutch in a Nich knows that some other Nutch Would like to move into his Nich very much. So each Nutch in a Nich has to watch that small Nich or Nutches who haven't got Niches will snitch. “On beyond zebra”, Dr. Suess (Geisel, 1955)

Niches: fundamental and realized fundamental niche The fundamental niche is defined by an organism’s adaptations to persist in a given abiotic environment realized niche The realized niche of an organism is often smaller than the fundamental niche due to competition, predation, parasitism, and recruitment limitations

2. Predation (+/-) broadly defined Predation - one organism kills and eats another Parasitism Herbivory Parasitoids Pathogens

Predation - broadly defined Parasitism - one organism feeds from or benefits from another, at the other’s expense Herbivory Parasitoids Pathogens Fig. 33.12 Ak picture Mosquito - ectoparasite Tapeworm - endoparasite

Predation - broadly defined Parasitism Herbivory - animal eats a plant. -Some like predation (whole plant consumed) - Some like parasitism (only parts consumed, individual not killed). Parasitoids Pathogens

Predation - broadly defined Parasitism Herbivory Parasitoids - eggs laid inside host, larvae kills…eventually Pathogens Ricklefs Fig. 17.2

Predation - broadly defined Parasitism Herbivory Parasitoids Pathogens - cause disease, usually microscopic (virus, bacteria, protists, some fungi)

Predation - adaptations of predators and prey Cryptic coloration Aposematic coloration Mimicry (Batesian and Müllerian)

3. Mutualism (+/+) Mutualism vs. symbiosis Currency - who gets what? Corals: anthozoan + dinoflagellate (fig. 33.6) Ants/Acacia’s Mycorrhizae: plant + fungus (Raven et al. 1999)

Mutualism (+/+) Specific vs. generalist

Mutualism (+/+) Obligate vs. facultative Lichens Coral bleaching http://www.aims.gov.au/pages/research/coral-bleaching/coral-bleaching.html Ants and aphids http://www.ent.iastate.edu/imagegal/homoptera/aphid/soybeanaphid/soybaphidants.html

Coevolution Reciprocal evolutionary adaptations between two interacting species. Each species is a strong selective force on the other. One species adapts to the second, and these changes engender new adaptations in the second, which cause further change in the first…and so on. NOT just with mutualisms! Tough to demonstrate.

B. Which interactions structure communities? Ecobeaker Demo: intertidal barnacle distributions

III. Community structure A. Measures of diversity B. Trophic structure

III.A. Measures of diversity Species richness - the number of different species present in a system Species evenness (relative abundance) - proportion of community biomass or number of individuals contributed by each species

Richness and Evenness Fig. 53.21

Relative abundance Typically only a few species are common, many more are in moderate abundance, some are quite rare.

III.B. Trophic structure Food chains Food webs - Strength of interactions length of food- chains harder to denote exact trophic level. Richness and evenness typically look at species within a trophic level, e.g., plants. When looking across levels, start assessing trophic structure. Trophic just means “eating” – e.g., autotroph, heterotroph. Food webs – relative strength of interactions matter (“interaction coefficients”) Fig. 53.11 Fig. 53.10

III.B. Trophic structure What limits the length of a food chain? Energy? (Fig. 54.11)

III.B. Trophic structure What limits the length of a food chain? Stability? (Fig. 53.10)

III.B. Trophic structure What limits the length of a food chain? Energy - Queensland tree holes (Fig. 53.13)

IV. Control of community structure A. Dominant and keystone species B. Top-down vs. bottom-up control C. Disturbance and succession D. Biogeography