Chapter 4: Biological Communities and Species Interactions Understand the fundamental factors...

Chapter 4: Biological Communities Chapter 4: Biological Communities and Species Interactionsand Species Interactions

Understand the fundamental factors driving community development

I. Who Lives Where and Why?I. Who Lives Where and Why?

A. Critical Factors and Tolerance Limits– Examples of limiting conditions are

temperature, moisture levels, nutrient supply, and soil

– Liebig’s principle (law) states, the single factor in shortest supply relative to demand is the critical determinant to species distribution

• Called the principle of limiting factors


A. (cont)– Shelford used Liebig’s principle to formulate

that there are maximums and minimums for environmental factors (resources)

• Called tolerance limits• Zones of intolerance are areas of species extinctions

in that habitat• The factor closest to the zone of intolerance

determines where an organism can survive• Sometimes called Shelford’s Law


A. (cont)– Some variations of the 2 rules exist

• Could be multiple factors working together to limit distribution

– Some organisms have a specific critical factor• Passenger Pigeons (land), Saguaro Cacti (cold)

– Some limitations may occur during a specific portion of the life cycle

• Desert Pupfish (temperature and salinity levels for juveniles only)


A (cont)– Indicator species are species with defined

tolerance limits and are used to indicate the health of the habitat

• For some, if missing there is a problem• For some, if present there is a problem

– Environmental indicators are species of organisms which can give specific information about a habitat

• May indicate specific nutrients present or missing• May indicate pollution


B. Natural Selection, Adaptation, and Evolution– 1. General Information

• Organisms adapt to special conditions– One form of adaptation is acclimation

• Organisms experiences physiological modifications or changes

• Non-permanent, reversible– Another form is genetic, part of evolution

• Will change the population• Inheritance of specific traits• Natural selection allows the organism “best

suited” for an environment to reproduce

Darwin’s FinchesDarwin’s Finches


B. (cont)• Acts on pre-existing genetic diversity

– Mutations can add to the genetic diversity

• Genes that suit the environment will become the dominant trait over time

• Darwin’s finches is a good example– Common, general ancestor becoming specialized

multiple current species

• Also called selective pressure


B. (cont)– Factors affecting selective pressure are

• Physiological stress due to inappropriate levels of some critical factors

• Predation, parasitism and disease• Competition• Luck?

• Geologic isolation can aid in different gene expression

– Possibly leading to speciation


B. (cont)• Natural Selection and Adaptation can cause

similar species or 2 groups of the same species to drift genetically apart

– Called Divergent Evolution

• Natural Selection and Adaptation can cause 2 different species to drift genetically together (considered the same species)

– They look and act alike– Called Convergent Evolution


C. The Ecological Niche– 1. General Information

• Habitat is the place where an organism lives• Ecological niche is a description of the role

of a species in a biological community– Niches can change as physical characteristics

change


C. (cont)– 2. Law of competitive exclusion

• States that no two species will occupy the same niche and compete fro exactly the same resources in the same habitat (for a long period of time)

• Creates niche specialization, which creates behavioral separation, when two niches overlap

Paramecium GraphParamecium Graph

Resource partitioning and niche Resource partitioning and niche specializationspecialization


C. (cont)– 2 (cont)

• The number of niches is determined by the resources and the extent by which they can be separated

– Some animals can share resources, but use them at different times

• Ex. Owls and Hawks, Bats and Mockingbirds

– Some animals can use the same resources, but use different portions of the same resource

• Ex. Finches, MacArthur's Warblers, Flickers and Woodpeckers

MacArthur's Warblers : Splitting the MacArthur's Warblers : Splitting the same resourcesame resource

Left to right: Cape May, Yellow-rumped, Black-throated Green, Left to right: Cape May, Yellow-rumped, Black-throated Green, Blackburnian, and Bay-breasted Warblers. Black areas in stylized conifers Blackburnian, and Bay-breasted Warblers. Black areas in stylized conifers show where feeding is concentrated.show where feeding is concentrated.

II. Species Interactions and II. Species Interactions and Population DynamicsPopulation DynamicsA. Predation

– An organism that feeds directly on another organism (living)

• Yes, Herbivores are predators!• Scavengers, detritovores and decomposers

(that feed on dead organisms) are NOT predators

• Parasites? , pathogens

– Predation is an influence on population balance in a community

II. Species Interactions and II. Species Interactions and Population DynamicsPopulation Dynamics

A. (cont.)• Involves 3 scenerios

– 1. Influences all stages of the life cycle for both predators and prey– 2. influences food obtaining mechanisms– Influences prey- predator adaptations to resist or encourage

predation

– As prey species mature, the predators change– As predators mature, the prey species change– Tend to be the most successful with the old and the

young (book says least fit)– Some prey have created defenses

• Spines, thorns, thicker bark, poisonous chemical mimicry, speed, etc

II. Species Interactions and II. Species Interactions and Population DynamicsPopulation DynamicsB. Keystone Species

– A species or group of species whose impact on its community is much larger and more influential than would be expected from mere abundance

– At one time they were thought to be top predators

– May be a species that has a significant impact on other organisms

• Ex: tropical figs, sea otters, prairie dogs

Keystone Species: Prairie DogsKeystone Species: Prairie Dogs

Keystone Species: Sea OttersKeystone Species: Sea Otters

Keystone Species: American BeaverKeystone Species: American Beaver


B. (cont.)– In some conditions microscopic organisms

may be the keystone species• Ex: mycorrhzae (root fungus)

C. Competition– When organisms compete over resources– 2 types:

• Interspecific: between organisms of different species• Intraspecific- between organisms of the same species

Interspecific CompetitionInterspecific Competition

Intraspecific Competition: Intraspecific Competition: TerritoriesTerritories


C. (cont.)– Interspecific competition is responsible for

niche specificity– Physically designed to tolerate conditions,

acquire foods, and reproduce at a time different from competitors

• Animal kingdom’s “arms race”• Bigger, stronger, faster, and smarter

– Avoids fighting as much as possible

– Where 2 different species that occupy the same niche compete in a habitat, one species will out compete the other

II. Species Interactions and II. Species Interactions and Population DynamicsPopulation DynamicsC. (cont)

• Described as the Lotka-Volterra Competition Model

• Mathematical equations to predict which species will out compete the other

• Depends on 2 factors– 1. The number of individuals of species 2

present; and (2) the intensity of the interference with species 1’s growth; or the intensity of the competition of species 2 on species 1

– It will be a negative factor

Lotka-Volterra Competition Model Lotka-Volterra Competition Model

II. Species Interactions and II. Species Interactions and Population DynamicsPopulation DynamicsC. (cont.)

– Intraspecific competition is more intense

• Battling with organisms with the exact same set of needs

• Plants have to battle with mature adults• Adaptive tendencies lead to greater

dispersal of seeds• Territories are a direct result of intraspecific

competition


C. (cont.)• Battle for an area with all of the needs of the

organism at all stages of the life cycle– Those animals without all either don’t reproduce or don’t

reproduce successfully

D. Symbiosis– Interactions between species

• Not always antagonistic

– Intimate living together of members of two or more species

II. Species Interactions and II. Species Interactions and Population DynamicsPopulation DynamicsD. (cont.)

– 4 types of symbiosis• Commensalism- one benefits while another

has no apparent effect• Mutualism- both organisms benefit• Predator/Prey- one benefits while the other

dies• Parasitism- one benefits the other has no

effect or bad effect

II. Species Interactions and II. Species Interactions and Population DynamicsPopulation DynamicsE. Defensive Mechanisms

– Toxic chemicals, body armor, similar coloration, and others to defend against predation

• Poison ivy, thorns• Batesian mimicry• Mullerian mimicry, 2 different species

unpalatable and dangerous looking very similar

III. Community PropertiesIII. Community Properties

General Information– Try to understand the factors which make up

the properties involving communities• Productivity, diversity, complexity, resilience,

stability, and structure

A. Productivity– Photosynthetic rates are regulated by light

levels, temperature, moisture, and nutrient availability.


A. (cont.)– Corn and sugar cane; under ideal

conditions, in the tropics can approach productivity as high as the rain forest

– A very small amount of available sunlight is captured by photosynthetic communities

B. Abundance and Diversity– Abundance is the total number of

organisms of a species in an area


B. (cont.)– Diversity is the number of different

species in an area– Abundance and diversity are inversely

related• High abundance means low diversity• High diversity means low abundance

– Diversity decreases away from the equator and toward the poles


B. (cont.)– Abundance increases away from the

equator and toward the poles– Diversities decreases moving upward in

attitudeC. Complexity and Connectedness

– Complexity is the number of species at each trophic level and the number of trophic levels in a community


C. (cont.)• A diverse community may not be a complex

community• Tropical rainforests have many trophic

levels that are compartmentalized – Called guilds

• Species that occupy the same trophic level• Fruit enters, leaf nibbles, seed gnawers, etc


D. Resilience and Stability– 3 Types

• 1. constancy, lacks fluctuations in composition and function

• 2. inertia, which indicates resistance to perturbations

• 3. renewal, which is the ability to repair damage after disturbances


D. (cont)– MacArthur believed the more complex a

community the more stable and resilient the community will be when disturbed (studies show no real consistency with this conclusion)

– Disturbances are based on the organism

• Ex. Earthquakes, flooding, traveling, spitting, etc.


E. Edges and Boundaries– Areas between 2 adjacent and different

communities– Edge effect is the relationship of communities

and the organisms that inhabit the edge of the 2 communities or habitats

• Considered secondary habitats

– Some boundaries are sharp and distinct, called edges


E. (cont)– When the 2 habitats or communities blend

together, it is called a boundary– Edges and boundaries are also called

Ecotones• Sharp divisions are called closed communities• Boundary divisions where many species cross are

called open communities

– Adjacent communities may be important for species that need both types during different stages of development in the life cycle

IV. Communities in TransitionIV. Communities in Transition

A. Ecological Succession– Transition of communities in an area

over time– 2 types

• Primary Succession – development starts with a site that is newly broken rock or an area unoccupied previously by organisms

– Starts with pioneer species, such as lichens and bacteria


A. (cont)• Secondary Succession – an existing

community is disrupted and a new, previous, community redevelops in the habitat or community

– Caused by wildfires, or farmland restoration• Starts with weeds or grasses, when dealing

with a fire (depends on the severity of the fire)

• Starts with grasses and shrubs when dealing with overgrown farmland


A. (cont)• Typical primary succession

– Rocks, lichens, weeds, grasses, shrubs, conifers, deciduous trees (TDF)

• Typical secondary succession– Climax community, fire, weeds, grasses, shrubs,

coniferous trees, deciduous trees– May be much faster and may skip some steps,

depending on what community surrounds the fire area and what plants are ready to spread seeds into the open area


B. Introduced Species and Community Change– Introduced species are non-native species – They can replace existing organisms or (by out

competing them for the same resources) or– They can wipe out an unintended species

• Ex. Mongooses in Hawaii

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Chapter 4: Biological Communities and Species Interactions Understand the fundamental factors...

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