Interactions: Populations and Communities Population Interactions - - PowerPoint PPT Presentation

Interactions: Populations and Communities

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

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

Ecosystem Stability

Abiotic and Biotic Factors Affect Stability

• The stability of populations, communities and

ecosystems is affected by interactions with abiotic and biotic factors

• Examples: food chains and food webs, algal

blooms, species diversity, population density

Food Chain Stability

Food Web Stability

Algal Bloom

• Rapid increase in the population of algae in an

aquatic ecosystem

• Usually caused by an excess of nutrients, such

as phosphorus (abiotic factors)

• Why are algal blooms harmful?

Species Diversity Within Ecosystems

• Diversity of species within an ecosystem may

influence the stability of the ecosystem – Keystone species – Producers – Essential abiotic and biotic factors

Keystone Species

• A species that is not necessarily abundant in a

community yet exerts strong control on community structure by the nature of its ecological role or niche

• Removal of a keystone species often results in

the collapse of the ecosystem Examples: Sea otters, sea star, tiger sharks

Pisaster ochraceus

Cooperative Interactions

Competition and Cooperation

• Competition and cooperation are important

aspects of biological systems

• Cooperative interactions within organisms

promote efficiency in the use of energy and matter

– Cellular level – Multicellular organisms – Populations of unicellular organisms

Cooperative Interactions

• Cellular level: Plasma membrane, cytoplasm

and, for eukaryotes, the organelles contribute to the overall specialization and functioning of the cell

Cooperative Interactions

• Multicellular organisms: specialization of
• rgans contributes to the overall functioning
• f the organism

– Exchange of gases – Circulation of fluids – Digestion of food – Excretion of wastes

Cooperative Interactions

Cooperative Interactions

• Interactions among cells of a population of

unicellular organisms can be similar to those

• f multicellular organisms
• Interactions increase efficiency and utilization
• f energy and matter

Example: Deep sea vent community

Deep Sea Vent Community

• Bacterial community in and around deep sea

vents

• Chemosynthetic bacteria are the primary

producers of the food chains of hydrothermal vents

• Symbiosis: chemosynthesizers and respiring

heterotrophs

Quorum Sensing

• Another example of cooperative interactions

between bacteria of the same species and different species

• Used to coordinate certain behaviors such as

biofilm formation and virulence, based on the local density of the bacterial population

Ecological Succession

• Succession: the process of change in the

species structure of an ecological community

• ver time

– Primary succession – bare rock or sand, no soil present – Secondary succession – soil is established – Pioneer species – the first species to arrive, differ between primary and secondary succession

Primary Succession

Secondary Succession