1 Outline The Concept of the Community – Diversity and Composition Models The Structure of Communities – Island Biogeography – Habitat and Ecological Niche – Competition Between Populations – Predator-Prey Interactions – Symbiotic Relationships Community Development Community Biodiversity

2 Community Concept An assemblage of populations interacting with one another within the same environment – Composition is a listing of various species in the community – Diversity includes both species richness and species diversity

3 Community Structure

4 Diversity and Composition Models Gleason - Individualistic Model – Each population is there because its abiotic requirements are met Clements - Interactive Model – Community is the highest level of organization – Dependent on biotic interactions

5 Species Richness of Communities

6 Island Biogeography MacArthur and Wilson – Developed a general model of island biogeography – Explains and predicts how the community diversity of an island is affected by Distance from the mainland, and Size of the island

7 Model of Island Biogeography

8 Habitat and Ecological Niche Habitat – The area an organism lives and reproduces in Ecological niche – The role a species plays in its community Includes its habitat, and Its interactions with other organisms – Fundamental niche - All conditions under which the organism can survive – Realized niche - Set of conditions under which it exists in nature

9 Feeding niches for Wading Birds

10 Community Structure Competition When two species compete, the abundance of both species is negatively impacted Predation (or parasitism) Expected to increase the abundance of the predator (or parasite) And reduce the abundance of the prey (or host)

11 Competition Between Populations Interspecific competition – Members of different species require the same resource – The supply of the resource is limited

12 Competition Between Two Laboratory Populations of Paramecium

Competitive Exclusion Principle No two species can occupy the same niche at the same time Resource Partitioning decreases competition Can lead to character displacement Competition Between Populations

14 Character Displacement in Finches on the Galápagos Islands When on the same island, the beak sizes are appropriate for eating small, medium, and large-sized seeds. When on separate islands, beaks have the same intermediate size, allowing them to eat seeds that vary in size.

15 Niche Specialization Among Five Species of Coexisting Warblers

16 Competition Between Two Species of Barnacles

17 Predator-Prey Interactions Predation – One living organism, the predator, feeds on another, the prey Predator is larger Predator has lower reproductive rate Prey usually entirely consumed – Presence of predators can decrease prey densities, and vice-versa

18 Predator-prey Interaction Between Paramecium caudatum and Didinium nasutum Didinium ate all the Paramecium and then dies out

19 Predator-prey Interaction Between a Lynx and a Snowshoe Hare

20 Prey Defenses Prey defenses – Mechanisms that thwart the possibility of being eaten by a predator Spines Tough Epidermis Poisonous Chemicals Camouflage (cryptic coloration) Bright Coloration (warning coloration) Flocking Behavior

21 Camouflage in the Anglerfish 9Y_3TNc

22 Mimicry – One species resembles another species – Mimicked species possesses an overt antipredator defense (warning coloration) Batesian Mimicry - Mimic lacks defense of the organism it resembles Müllerian Mimicry - Mimic shares same protective defense

23 Anti-predator Defenses Poison arrow frog used to make arrows lethal weapons. Eastern tiger swallowtail butterfly caterpillar has false eyespots to confuse predator. South American lantern fly has a large false head that resembles and alligator.

24 Mimicry Among Insects with Yellow and Black Stripes

25 Symbiotic Relationships Symbiosis – Interactions in which there is a close relationship between members of two species – Parasitism Parasite derives nourishment from a host, and may use host as habitat and mode of transmission – Endoparasites -Inside host body – Ectoparasites – Outside host body Beetle infected with wasp larvae Fleas on your dog/cat/you

26 Commensalism Symbiosis, cont. – Commensalism A symbiotic relationship in which one species benefits and the other is indifferent – Remoras and Sharks Many supposed examples may turn out to be mutualism or parasitism Inferred amount of harm or benefit two species do to one another is subject to investigator bias

27 Clownfish Among Sea Anemone’s Tentacles

28 Mutualism Symbiosis, cont. – Mutualism A symbiotic relationship in which both members of the association benefit Need not be equally beneficial to both species – Cleaning Symbiosis Often help each other obtain food or avoid predation – Bacteria in human intestinal tract

29 Mutualism Between the Bullhorn Acacia Tree and Ants a. Tree provides nourishment for ants. Ants live inside hollow thorns. b. Nectaries at base of leaves from which ants feed. c. Ants harvest larval food at tips of leaves

30 Cleaning Symbiosis

31 Community Development Ecological Succession – A predictable pattern of change in species replacements following a disturbance Primary Succession occurs in areas where there is no soil formation Secondary Succession begins in areas where soil is present – Pioneer Species

32 Secondary Succession

33 Secondary Succession in a Forest

34 Succession Models Facilitation Model – Each stage facilitates invasion and replacement by organisms of the next stage – Succession in a particular area will always lead to the same type of community – Climax Community

35 Succession Models Inhibition Model – Colonists remain and inhibit growth of other plants until the colonists are damaged or die Tolerance Model – Different types of plants can colonize an area at the same time – Chance determine which seeds arrive first

36 Community Diversity Community stability can be recognized in three ways – Persistence through time – Resistance to change – Recovery once a disturbance has occurred

37 Intermediate Disturbance Hypothesis If widespread disturbances occur frequently, diversity will be limited If diversity is high, only moderate disturbances have been occurring with moderate frequency

38 The Intermediate Disturbance Hypothesis

39 Predation, Competition, and Biodiversity Predation by a particular species may reduce competition and increases diversity – Such predators are referred to as keystone predators Exotic species – May lead to unbridled competition – Resultant reduction in biodiversity

40 Effect of a Keystone Species

41 Review The Concept of the Community – Diversity and Composition Models The Structure of Communities – Island Biogeography – Habitat and Ecological Niche – Competition Between Populations – Predator-Prey Interactions – Symbiotic Relationships Community Development Community Biodiversity