Notes

Outline

Introduction to Ecology CERC Certificate Program Columbia University Session 3 – Community Ecology

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Ecological Footprint Exercise We have an impact on the Earth Responses? Critiques of the calculations?

Population Growth Exercise What did you find? Describe the curves – what was happening when? When would you get population oscillations in the Logistic Model? Approximate K for humans?

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Exponential Population Growth Equation Derivation The equation for population change over a unit t (time) DN / Dt = No + B + I - D – E Simplify the equation Assume a closed population Eliminate migration (I, E) DN / Dt = No + B - D Growth rate r = (B/N) – (D/N) DN / Dt = (r)(No) This is the basic exponential growth equation

Logistic Population Growth Equation Derivation Add the Carrying Capacity (K) – how? DN / Dt = (r)(No) Base Expon. Equation DN / Dt = (r)(No)(1-(N/K)) Base Logistic equation

Growth Matters! r-selected species Why most weeds are weedy Edge species are typically r-selected Invasive species are often r-selected

Growth Matters! K-selected species Why we don’t get many species of oaks in most young forests? Climax communities Susceptible to habitat fragmentation

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Why is This Field Important? Useful for conserving entire communities Repopulating barren lands Determining most important species to conserve Predicting how communities will recover, after disturbance Predicting community resilience to disturbance Quantifying what is present for conservation and where it would be

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Community Definition “an association of interacting populations, usually defined by the nature of their associations or the habitat they use” Key features: Several species One area

What Structures a Community? Abiotic Climate Latitude Proximity to Ocean Disturbances (abiotic) Biotic Interspecific Interactions Keystone Species Disturbances (biotic) (Intraspecific Interactions?)

Types of Interspecific Interactions

Niches Definition? 1. The ecological role played by a species in a community 2. An n-dimensional hypervolume Huh?

Niche = N-dimensional Hypervolume Dimensions are the limiting factors pH, soil type, humidity, temperature, nesting space, mates, parasites, etc. Niche use determines community formation

General Types of Communities Closed sharp boundaries abrupt ecotones distinct associations between species Open boundaries are vague, gradual little or no association between species

How Do Communities Form? Neutral Assembly Species in a community come together not necessarily due to the presence of other species Due to other idiosyncratic, species-specific influences Community Assembly Rules Repeatable patterns of how communities form Sequence of adding species is important Deterministic patterns, including max # of spp present Can this be tested?

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Island Biogeography Full Title: “Equilibrium Theory of Island Biogeography” Assertions re: # species: Near > Far Bigger > Smaller There is an equilibrial number of species Advocates for CAR?

Island Biogeography Research Florida Keys - mangrove islands Gassed several islands to kill all insects on mangroves Observed return rates of species Counted number and trophic type Occurred in early 1970’s

Island Biogeography Results Size of Island (long-horn beetles) Species-Area Relationship

Island Biogeography Conclusions Supported main assertions Assertions re: # species: Near > Far Bigger > Smaller There is an equilibrial number of species Spawned a great deal of additional research by many others One of two main proponents (Simberloff) no longer agrees with equilibrial assertion

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Keystone Species The most important species Structures the community What is the origin of the term? Contributes greatest amount to ecosystem functioning Controlling herbivores Terminal Predators are most commonly thought of here Decomposition Produces greatest amount of biomass?

Keystone Species Usually thought of as Strong interactors Tightly woven into the fabric of the food web The species that is the very strongest interactor Definition #2: The species that, when removed, leads to a total breakdown of the food web

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Succession Definitions Chronological distribution of organisms within an area The sequence of species within a habitat or community through time Shared: Time Single area

Succession Types – by Habitat Primary New habitat from barren ground

Succession Types – by Process Degradative Consumption of a finite resource Allogenic Requires ongoing extrinsic environmental changes Autogenic Intrinsic factors within the community

Applications of Succession Can you think of any?

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Measuring Biodiversity Aspects of biodiversity to measure?

Diversity Indices Used to compare sites or evaluate a single one through time Many many many types Main ones: Shannon (diversity) Simpson (diversity) Rarefaction (richness) Sorenson (comparative diversity)

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Global Distribution of Biodiversity Greatest in areas where NPP is greatest Terrestrial: toward Equator  - Why? Aquatic: near shore, marine upwellings – Why?

Community Ecology Why is this field important? What is a community: Community Classifications Island Biogeography Keystone Species Succession Measuring Biodiversity Global Distribution of Biodiversity Community Stability and Diversity

Relationship Between Community Diversity and Stability Stability components Resistance Resilience Recovery speed Biodiversity has been thought to influence Stability Croplands – Unstable Tropics – Stable Jury still out preliminary work seems to support this

Assignment for Next week: Forensic Entomology! Learn more about the application of community ecology and succession to solving crimes Instructions are all online, and available here Turn in next week via email We will discuss it then

Proximate Ecological Fields - Next Week: Trends down pyramid: Increase in geographic scale From single species to multiple species Increasing number of ecological factors that may  be influential Decreasing certainty in results

Next Week: The Tour of Ecology Continues Population ecology Community ecology Ecosystem ecology Next week’s emphasis Conservation Issues