Community Ecology How do organisms interact?

Community Ecology  Ecologists use 3 characteristics to describe a community: 1. Physical Appearance: size, stratification, & distribution of its pops 2. Species Diversity: combination of  Species richness: # of different species  Species evenness: abundance of individuals within each species 3. Niche structure: # of niches and species interactions

Community Ecology  Species Diversity  Changes in species diversity can be based on latitude:

 Species Diversity  Pollution can also change the species diversity in an ecosystem Community Ecology

 Species Equilibrium Model  aka Theory of Island Biogeography  A balance between two factors determines the number of different species found on an island: rate at which new species immigrate to the island & rate at which existing species become extinct on the island  Three factors must be taken into account: 1. Immigration and extinction rates 2. Island size 3. Distance from mainland Community Ecology

 Species Equilibrium Model  Immigration & Extinction reach an equilibrium that determines the island’s average number of species

Community Ecology  Species Equilibrium Model  Large islands have larger equilibrium number of species b/c larger target for immigration & more resources and niches (less extinction)

Community Ecology  Species Equilibrium Model  Islands closer to a mainland will have higher immigration  higher equilibrium # of species

Community Ecology  Remember the Major Roles that Species Can Play within Ecosystems cont.: 1. Native 2. Nonnative 3. Indicator 4. Keystone 5. Foundation species

Community Ecology  Species Interactions: 5 Basic Types 1. Interspecific Competition  = Competition between two species for shared or scarce resources (food, space, etc.)  Occurs when niches overlap  Gause’s principles states that not 2 species can occupy the same niche at the same time  1 species must relocate, die out or change niche

Community Ecology  Species Interactions: 5 Basic Types  Over a time scale long enough for natural selection Resource Partitioning can occur:  = Species minimize competition by filling specific niches within an ecosystem (traits allow them to utilize resources at different times, locations or ways)  Ex: North American warblers hunt for insects in same spruce trees, but at different parts & times

Community Ecology  Species Interactions: 5 Basic Types 2. Predation  An interaction between animals in which one organism (predator) captures and feeds upon another (prey)

Community Ecology  Species Interactions  Preys’ Defense Mechanisms:  Physical adaptations: highly developed sight & smell; shells; spines; thorns  Camouflage & mimicry  Chemicals: poisons, irritants, odors, ink clouds  Behaviors: puffing up, mimicking a predator, playing dead

Community Ecology  Preys’ Defense Examples: Hognose snake Praying mantis Cuttlefish

Community Ecology  Species Interactions: 5 Basic Types continued  Symbiotic Relationships  = An interactive association between two or more species living together 3. Parasitism: when one organism (parasite) feeds on or otherwise harms another organism (host) in close association 4. Commensalism: benefits one species but has little or no effect on other species 5. Mutualism: interaction benefitting both species

Community Ecology  Species Interactions: 5 Basic Types 3. Parasitism: when one organism (parasite) feeds on or otherwise harms another organism (host) in close association (+,-) Different from predation in that parasite is generally smaller than host and doesn’t kill host Brood parasitismMistletoeTick

Community Ecology  Species Interactions: 5 Basic Types 4. Commensalism: benefits one species but has little or no effect on other species Epiphytes (Bromeliads & some Orchids)& Trees Whales & Barnacles

Community Ecology  Species Interactions: 5 Basic Types 5. Mutualism: interaction benefitting both species Pollination Mutualism Nutritional Mutualism: Lichen (fungi & algae) Gut Inhabitant Mutualism

Community Ecology  All communities change their structure & composition over time in response to each other & changing environmental conditions  Ecological Succession  = gradual change in species composition (which species are present)  Two Types:  Primary Succession  Secondary Succession

Community Ecology  Primary Succession: the gradual establishment of biotic communities on lifeless ground Pioneer Species (Lichens, Algae, Bacteria, Moss) Pioneer Species start soil formation process: trap soil particles & detritus in wind, secrete acids to break down rock Late successional species Mid successional species End in Climax Community (long-lived hardwoods)

Community Ecology  Secondary Succession: when biotic communities are established in an area where some type of biotic community is already present  Occurs after disturbance (burned forest, polluted stream, abandoned farmland)

Community Ecology  Ecological Succession  Disturbances: change in environmental conditions that disrupts a community or ecosystem  These disturbances can range from mild to catastrophic and can be caused by natural occurrences or human activities: Fire Drought Flooding Mining Clear-cutting Plowing Pesticides/Herbicides Climate Change Nonnative Species Invasion

Community Ecology  Ecological Succession  Intermediate Disturbance Hypothesis: communities that experience fairly frequent but moderate disturbances have the greatest species diversity

Community Ecology  Measuring Biodiversity  Shannon’s Diversity Index (H): range from 0 to 5 (more diverse)  Simpson Diversity Index (D): range from 0 (zero diversity) to 1 (infinite diversity)

Community Ecology  Shannon’s Diversity Index H = the Shannon Diversity index P i = fraction of the entire population made up of species i (n i /total) S = numbers of species encountered ∑ = sum from species 1 to species S s H = -∑ (P i * ln P i ) i=1

Community Ecology  Simpson Diversity Index D = the Simpson Diversity index n i = number of individual per species N = total number of individuals S = numbers of species encountered ∑ = sum from species 1 to species S s D = 1 -∑ [(n i / N) 2 ] i=1

Communities  Shannon’s Diversity Index  High values of H would be representative of more diverse communities.  If the species are evenly distributed then the H value would also be high. So the H value allows us to know not only the number of species but how the abundance of the species is distributed among all the species in the community. BirdsNiNi PiPi ln P i - (P i * ln P i ) Pigeon Robin Starling Crow House Sparrow H = 0.223