Biological Populations, Ecosystem Dynamics, and Species Interactions
Biological Organization and Ecosystem Dynamics
Organism: A living thing that is capable of functioning on its own.
Species: A group of organisms that:
Resemble each other closely.
Are similar in genetic makeup, chemistry, and behavior.
Are able to interbreed and produce fertile offspring.
Interspecific: A term defined as occurring between or involving different species.
Population: A group of organisms belonging to the same species that interact with each other and occupy a specific geographical area.
Community: A biological collective consisting of populations of different species living together in a defined habitat.
Ecosystem: A functional system comprising a community of living (biotic) organisms interacting with the non-living (abiotic) components of their environment through various nutrient and energy cycles.
Ecological Niches and Adaptations
Ecological Niche: A particular area within a habitat occupied by an organism, as well as the complete function and role of that organism within its ecological community.
Physical Environment Influence: The physical environment influences both how organisms affect their ecosystem and how they are affected by available resources and competitors.
Evolutionary Basis: An ecological niche reflects the specific adaptations that a species has acquired throughout its evolutionary history.
Core Characteristics of a Niche:
The specific physical habitat.
Interactions with both living (biotic) and non-living (abiotic) environmental factors.
The exact place and functional role within the food web.
The specific types and amounts of resources available.
Generalist vs. Specialist Species
Generalist Species:
Niche Width: Live in broad niches.
Dietary Range: Able to survive on a wide variety of food resources.
Environmental Tolerance: Able to withstand a wide range of physical and chemical environmental conditions.
Examples: Cockroaches, humans, and mice.
Specialist Species:
Niche Width: Live in narrow niches.
Dietary Range: Depend on a specific or limited number of prey items.
Environmental Vulnerability: Sensitive to environmental changes and highly prone to extinction.
Examples: Giant pandas, koalas, and mountain gorillas.
Interspecific and Intraspecific Interactions
Symbiosis: A broad term used to describe any type of close and long-term biological interaction between two different biological organisms, which may belong to the same or different species.
Types of Symbiotic and Ecological Interactions:
Amensalism: An interaction between two species where one species suffers or is destroyed while the other species remains completely unaffected.
Example: The black walnut tree releases a chemical that kills neighboring plant species.
Commensalism: An interaction between two species where one organism benefits while the other species is unaffected (neither helped nor harmed).
Forms of Commensalism Include:
Using another organism for transportation.
Using another organism for housing or shelter.
Using something that another organism has created.
Mutualism: An interaction between two species where both participating species derive a benefit.
Parasitism: An interaction between two species where one species benefits at the expense of another species, which is harmed.
Predation: A biological interaction where predators hunt, capture, and kill their prey.
Opportunistic Predators: Kill and consume almost anything available.
Specialist Predators: Exclusively prey upon certain specific organisms.
Saprotrophism: A mode of nutrition where saprotrophs obtain their essential nutrients from dead or decaying plant or animal matter through the direct absorption of soluble organic compounds.
Evolutionary Driving Forces and Competition
Competition: The interaction among organisms seeking the same resource in an ecosystem (such as food, mating partners, or territory). It serves as the primary driving force of evolution.
Intraspecific Competition: Competition that occurs between members of the same species.
Interspecific Competition: Competition that occurs between members of different species.
Role in Predator-Prey Dynamics: Competition is particularly prominent in predator–prey relationships, where the predator actively seeks food while the prey seeks survival.
Resource Partitioning: Evolutionary strategies that minimize direct competition among species sharing common resources.
Morphological Partitioning: Occurs when two competing species share the same resource but have evolved slightly different anatomical structures to utilize that resource in different ways.
Spatial Partitioning: Occurs when competing species utilize the same resource by occupying distinct areas or microhabitats within the geographic range of the resource.
Temporal Partitioning: Occurs when two species eliminate direct competition by utilizing the same resource at different times of the day, season, or year.
Ecological Constraints: Law of Tolerance and Limiting Factors
Law of Tolerance: States that the existence, abundance, and spatial distribution of any species depend on the tolerance level of that species to both physical and chemical environmental factors.
If specific environmental factors exceed a species' minimum or maximum tolerance limits, those factors will directly control and limit the organism's overall abundance or geographic distribution.
Limiting Factor: Any non-living (abiotic) factor that restricts, controls, or prevents the growth and expansion of a biological population.
Terrestrial Ecosystem Limiting Factors:
Concentration and level of soil nutrients.
Total available amount of water.
Available light intensity and duration.
Ambient temperature conditions.
Aquatic Ecosystem Limiting Factors:
The pH of the water.
The concentration of dissolved oxygen.
Light penetration depth.
The degree of water salinity.
Predator-Prey Population Dynamics
Predator-Prey Cycles: Population fluctuations driven directly by the feeding relationship between two species.
Cyclical Sequence of Population Changes:
If the prey species rapidly multiplies, the increased availability of food causes the number of predators to increase.
As predator numbers rise, they consume large quantities of prey until the prey population dwindles.
With the reduction in the prey population, food becomes scarce, causing predator numbers to drop.
The reduction in predator pressure subsequently allows the prey population to recover and multiply again, perpetuating the cycle.