Communities Essential Knowledge Objectives 2.D.1 (b) and 4.B.3 (a) - - PowerPoint PPT Presentation

Interactions: Populations and Communities

Essential Knowledge Objectives 2.D.1 (b) and 4.B.3 (a)

Population Interactions

• A population of organisms has properties that

are different from those individuals that make up the population

• Cooperation and competition between

individuals contribute to these properties

Population Interactions

• Relationships among interacting populations

can be characterized by positive and negative effects, and can be modeled mathematically

Community Interactions

• Classified by whether they help, harm or have

no effect on the species involved

• Species interactions strongly influence the

structure of communities

• Community: A group of populations of

different species in an area

Examples of Community Interactions

• Interspecific competition (-/-)
• Predation (+/-)
• Herbivory (+/-)
• Symbiosis
• Parasitism (+/-)
• Mutualism (+/+)
• Commensalism (+/0)

Interspecific Competition (-/-)

• Individuals of different species compete for a

resource that limits their growth and survival

Competitive Exclusion

• Occurs in a community when two species

compete for limited resources

• The local elimination of the inferior

competitor is called competitive exclusion

• Two species cannot coexist permanently in a

community if their niches are identical

Competitive Exclusion

Resource Partitioning

(a solution to the competition problem)

• Resource partitioning is the differentiation of

niches that enables similar species to coexist in a community

• Ecological niche - the specific set of biotic and

abiotic resources that an organism uses in its environment

• Fundamental niche versus the realized niche

Resource Partitioning

Predation (+/-)

• An interaction in which one organism captures

and feeds on another organism

• Predator and prey
• What are some advantages of predation?

(Think!)

Canadian Lynx and the Hare

Herbivory (+/-)

• Interaction in which an organism eats parts of

a plant or alga

Plant Defenses Against Herbivory

• Chemical defenses – produce chemicals that are

toxic or taste bad

• Mechanical defenses – prickles, thorns, spines
• r trichomes
• Thigmonasty – responses to touch, leaves curl

up or close

• Leaf shedding or warning coloration

Symbiosis – Parasitism (+/-)

• A symbiotic relationship in which one
• rganism benefits at the expense of the other
• rganism

Symbiosis – Commensalism (+/0)

• A symbiotic relationship in which one
• rganism benefits and the other organism is

neither helped nor harmed

Symbiosis – Mutualism (+/+)

• A symbiotic relationship in which both
• rganisms benefit

Community Interactions

• Structure of a community is measured and

described in terms of its biodiversity, which is measured in species richness (total number of different species in a community), and the relative abundance of each species present

Community Interactions