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Populations, Communities,and Species Interaction

Chapter 3

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Outline:

• Critical Factors and Tolerance Limits• Adaptation and Natural Selection• Speciation• Taxonomy• Ecological Niche• Species Interaction• Population Growth• Community Properties and Structure• Succession

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Population,Communities & Species Interaction

• Why, where and How?• Why a particular organism lives in a

particular area? Where he lives and how it interacts with its environment?

• How he deals with environmental stresses?• Why one species is dominant over the other? • How species interact with each other in a

community to survive?

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Critical Factors and Tolerance Limits

• Environmental factors should be within tolerable limit for organims to survive

• Critical Factor - Single factor in shortest supply relative to demand is a critical determinant in species distribution. Tolerance Limits refer to minimum and

maximum levels beyond which a particular species cannot survive or reproduce.

- Many species exhibit tolerance limits that are more critical for young than adults.

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Tolerance Limits

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Adaptation

• Adaptation - Process where species acquire traits that allow them to survive in their environments. Limited range of physiological modifications. E.g transferring an indoor winter plant

outside to outside during spring . Inheritance of specific genetic traits allowing

a species to live in a particular environment.Is explained by the theory of Evolution

(Charles Darwin).

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Natural Selection

• Natural Selection - Describes process where better competitors survive and reproduce more successfully. Small, spontaneous, random mutations

occur in every population creating genetic diversity& one trait could be better than other, means of survival.

Limited resources or environmental conditions may exert selective pressure on a population (influence fertility or survivorship in nature).

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Factors Exerting Selective Pressure

• Physiological stress due to in appropriate levels of a critical environmental factor. Moisture, Light, pH, temperature

• Predation includes Parasitism, Disease

• Competition:

Some organisms when they move to new habitat, may be just lucky to survive than better suited.

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Speciation

• Given enough time, mutations may collectively allow a species to become better suited to new environmental conditions.

• Evolution sometimes creates entirely new species, physically distinct from their ancestors. Divergent Evolution- Separation of one

species into new species even though they occupy the same territory. Compare the Cheetahs with House cat.

Convergent Evolution- Unrelated organisms evolve to look and act alike. E.g Fruit eating Galapagos finch looks and behave like the parrots but they are genetically different.

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Taxonomic Naming System

• Binomial - based on Latin.• Taxonomic classification of Corn:

Kingdom - Plantae Phylum-Anthophyta Class-Monocotyledons Order-Commenales Family-Poaceae Genus -Zea Species-Zea Mays Refer pg 54 Table 3.1 for Humans .

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Ecological Niche

• Habitat - Set of environmental conditions in which a particular organism lives. Ecological Niche is described as either

A description of role played by a species in a biological community or

A total set of environmental factors that determines species distribution.

Generalists –A broad niche eg Racoons have a wide range of habitat.

Specialists – A narrow niche e.g Panda occupy a specific habitat.

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Resource Partitioning

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Ecological Niche

• Resource Partitioning - Alter behavior or physiology to minimize competition ( Move to other areas, or become extinct). Partition then allows several species to

utilize different parts of the same resource and co exists within a single habitat).

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Ecological Niche of Wood Warblers

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Weedy Species

• Opportunistic Species - Quickly appear when opportunities arise. Many weeds e.g the Dandelions

• Pioneer Species – The opportunistics can quickly colonize open, disturbed, or bare ground.They can be useful in minimising soil erosion or a nuisnance.

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SPECIES INTERACTION

• Predation Any organism that feeds directly on another

living organism is termed a predator. Predation influences population balance of

communities involving:- All stages of life cycles of predator and prey.- Specialized food-obtaining mechanisms.- Specific predator-prey adaptations.

Predation can exert selective pressures which is called co-evolution (both predator and prey adapt to suit the situation, both adapt to new situation and allow the sps to survive and evolve.

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Competition

• Intraspecific - Competition among members of the same species e.g Within a patch of grass,,some are tall, some dwarf,some, sickly looking….all plants of the same sps absorb the same nutrients for growth.

• To survive they are aided by: Dispersal ( e.g seed dispersal by wind, air , Rain Territoriality : Defending resource-rich area,

primarily against members of own species Resource Partitioning (to reduce intraspecies

competition, sps move away from area)• Interspecific - Competition between members of

different species for the same nutrients. E.g Different sps of birds feeding for the same plot of corn.

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Symbiosis

• Symbiosis - Intimate living together of members of two or more species for mutual benefits. Types: Commensalism - One member benefits while

other is neither benefited nor harmed.- Cattle and Cattle Egrets

Mutualism - Both members benefit.- Lichens (Fungus and cyanobacterium)

Parasitism - One member benefits at the expense of other.

Humans and Tapeworms

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Defensive Mechanisms

Batesian Mimicry (H.W Bates,1857)- Harmless species evolve characteristics that mimic unpalatable or poisonous species.E.g the Wasp & the longhorn beetle (Pg 60)

Mullerian Mimicry (F. Miller,1878) - Two unpalatable or dangerous species evolve to look alike.E.g several species of mushrooms looks alike and produce fungal toxin which may be deadly.

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POPULATION DYNAMICS

• Population Growth Exponential Growth - Growth as a percentage

of the whole :dN/dt=rN dN= change in numbers of individual Dt= change in time R= rate of growth N= no. of individuals in a population Biotic Potential - Potential of a population to

grow in the absence of expansion limitations (if nothing was limiting its expansion).

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Limiting Factors

• Population growth is regulated by internal ( Maturity , body size, hormones) & external factors (Food, habitat, interaction).

• Environmental Resistance (factors which reduce pop growth rates) Density-Dependent Factors - Mortality rates

increase as the density of the population increases. Pop density is dependent on: E.g: Disease, Stress, Predation

Density-Independent Factors - Effect on mortality rate is independent of population density.

- Abiotic conditions eg drought, frost may kill mosquito pop.immaterials of the number with which they started the pop.

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• Abundance -Total number of organisms in a community.

• Diversity - Number of different species, ecological niches, or genetic variation

• Complexity - Number of species at each trophic level, and the number of trophic levels, in a community.

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Resilience and Stability

• Constancy (Lack of fluctuation)• Inertia (Resistance to pertubation)• Renewal (Ability to repair damage)

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Community Structure

• Randomly Arranged Individuals live wherever resources are

available.• Clumped

Individuals cluster together for protection, assistance, or resource access.

• Regularly Arranged

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Community Structure

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COMMUNITIES IN TRANSITION

• Ecological Succession Primary Succession - A community begins

to develop on a site previously unoccupied by living organisms.

- Pioneer Species Secondary Succession - An existing

community is disrupted and a new one subsequently develops at the site.

- Ecological Development

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Primary Succession

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Ecological Succession

• Climax Community - Community that develops and seemingly resists further change.

• Individualistic Community - Species become established according to their ability to colonize and reproduce in a given area.

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