Chapter 54 Community Ecology

What is a Community? It is an assemblage of species living close enough together for potential interaction. Communities differ in their species richness, the number of species they contain, and the relative abundance of different species. Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

There are different interspecific interactions, relationships between the species of a community. Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Competition (-/-) Predation (+/-) Mutualism (+/+) Commensalism (+/o)

Competition. –Interspecific competition: can occur when resources are limited. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Ecological niche = the "role" a species "plays" in the ecosystem. An organisms use of biotic and abiotic resources in its environment

Contrast the ecological niche with the "habitat" which is the physical environment in which the organism lives.

The ecological niche of a species, therefore includes: species’ habitat abiotic & biotic interactions

No two similar species occupy the same niche at the same time.

Extinction of one species

G. F. Gause (1934) tested competitive exclusion principle Constant food supply extinction

Classic experiments confirm this. Fig Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Resource partitioning: splitting the niche

Sympatric species consume slightly different resources or use resources in slightly different ways Insect-eating warblers

Character displacement: two similar species evolve in such a way as to become different from each other by accentuating their initial minor differences

Allopatric vs Sympatric populations

Allopatric populations: Similar beak morphologies and eat similar sized seeds

Avoids competition

Predation. –A predator eats prey. –Herbivory, in which animals eat plants. –In parasitism, predators live on/in a host and depend on the host for nutrition. –Predator adaptations: many important feeding adaptations of predators are both obvious and familiar. Claws, teeth, fangs, poison, heat-sensing organs, speed, and agility. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Offset oscillations in the population sizes of the predator and prey Coevolution of predator and prey

–Plant defenses against herbivores include chemical compounds that are toxic. –Animal defenses against predators. Behavioral defenses include fleeing, hiding, self- defense, noises, and mobbing. Camouflage includes cryptic coloration, deceptive markings. Fig Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Mechanical defenses include spines. Chemical defenses include odors and toxins Aposematic coloration is indicated by warning colors, and is sometimes associated with other defenses (toxins). Devil scorpionfish backside

Mimicry is when organisms resemble other species. –Batesian mimicry is where a harmless species mimics a harmful one. monarch viceroy

Müllerian mimicry is where two or more unpalatable species resemble each other. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig monarch queen Cuckoo beeYellow jacket

blenny (Aspidontus taeniatus) mimics Hawaiian cleaner wrasse shortnose wrasse mimics Potter's angel which sports a defensive spine Mimicry

–Parasites and pathogens as predators. A parasite derives nourishment from a host, which is harmed in the process. Endoparasites live inside the host and ectoparasites live on the surface of the host. Parasitoidism is a special type of parasitism where the parasite eventually kills the host. Pathogens are disease-causing organisms that can be considered predators.

Mutualism is where two species benefit from their interaction. Commensalism is where one species benefits from the interaction, but other is not affected. Coral polyp & zooxanthellae

Coevolution and interspecific interactions. –Coevolution refers to reciprocal evolutionary adaptations of two interacting species. When one species evolves, it exerts selective pressure on the other to evolve to continue the interaction. -flowers and pollinators -hermatypic coral and zooxanthellae -predator and prey -parasite and host

Lobelia Hawaiian honeycreeper

The trophic structure of a community is determined by the feeding relationships between organisms. The transfer of food energy from its source in photosynthetic organisms through herbivores and carnivores is called the food chain. Trophic structure is a key factor in community dynamics Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Food Chains Artificial devices to illustrate energy flow from one trophic level to another Trophic Levels: groups of organisms that obtain their energy in a similar manner

Total number of levels in a food chain depends upon locality and number of species Highest trophic levels occupied by adult animals with no predators of their own Secondary Production: total amount of biomass produced in all higher trophic levels Food Chains

Antarctic Food Web

Keystone Species A species whose presence in the community exerts a significant influence on the structure of that community.

Paine’s study on Pisaster and blue mussels

An Ecological Mystery

Kelp Forests Keystone Species

An Ecological Mystery Long-term study of sea otter populations along the Aleutians and Western Alaska 1970s: sea otter populations healthy and expanding 1990s: some populations of sea otters were declining Possibly due to migration rather than mortality 1993: 800km area in Aleutians surveyed -Sea otter population reduced by 50%

Vanishing Sea Otters 1997: surveys repeated Sea otter populations had declines by 90% : ~53,000 sea otters in survey area : ~6,000 sea otters Why? - Reproductive failure? - Starvation, pollution disease?

Cause of the Decline 1991: one researcher observed an orca eating a sea otter Sea lions and seals are normal prey for orcas Clam Lagoon inaccessible to orcas- no decline Decline in usual prey led to a switch to sea otters As few as 4 orcas feeding on otters could account on the impact - Single orca could consume 1,825 otters/year

Ecological Succession The progressive change in the species composition of an ecosystem.

Ecological Succession Climax Stage New Bare Substrate Colonizing Stage Successionist Stage

Temperate Old-field Succession Pioneer Seral stage Years after abandonment HerbsGrassesShrubs Pine Forest Hardwood Forest Climax

Hanauma Bay Tuff Ring (shield volcano) Succession after Volcanic Eruption What organisms would appear first? How do organisms arrive, i.e., methods for dispersal? Volcanic eruption creates sterile environment

Mechanisms of Succession Facilitation Inhibition Tolerance Early species improve habitat. Ex. Early marine colonists provide a substrate conducive for settling of later arriving species. As resources become scarce due to depletion and competition, species capable of tolerating the lowest resource levels will survive. Competition for space, nutrients and light; allopathic chemicals. First arrivals take precedence.

r & K Selected Species Pioneer species- 1st species to colonize a newly disturbed area r selected Late successional species K selected low competitive ability short life span high growth rate higher maternal investment per offspring low reproductive output high reproductive output slow growth rate long life span high competitive ability r & K refer to parameters in logistic growth equation

Ecological Succession on a Coral Reef

Successional Models and their Impacts Case 1: No Disturbance (Competitive Exclusion Model) Case 2: Occasional Strong Disturbance (Intermediate Disturbance Model) Case 3: Constant Strong Disturbance (Colonial Model)

Case 1: No Disturbance (Competitive Exclusion Model) As the reef becomes complex, organisms compete for space. Dominant organism outcompetes other species. Occurs in stable environments. Results in low species diversity. Highly protected patch reefs within lagoons or protected bays Deeper water

Case 2: Occasional Strong Disturbance (Intermediate Disturbance Model) Storms and hurricanes allow for other species to move in Dominant species would not be allowed to reach competitive exclusion After each disturbance have a recovery period Area of high diversity

Case 3: Constant Strong Disturbance (Colonial Model) Constant exposure to disturbance Shallow environment High turnover of species r-selected species

Reef Case 3 Case 2 Case 1 Deep reef slope Reef slope beneath reef crest Near reef crest

Ecological Succession on a Coral Reef The Big Island

Ecological Succession on a Coral Reef

Successional Models and their Impacts

Ohia lehua succession

Because of their size and isolation, islands provide great opportunities for studying some of the biogeographic factors that affect the species diversity of communities. –Imagine a newly formed island some distance from the mainland. Robert MacArthur and E. O. Wilson developed a hypothesis of island biogeography to identify the determinants of species diversity on an island. Species richness on islands depends on island size and distance from the mainland Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Two factors will determine the number of species that eventually inhabit the island. –The rate at which new species immigrate to the island. –The rate at which species become extinct. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

Studies of plants on many island chains confirm their hypothesis. Number of plant species on the Galapagos Islands in relation to the area of the island