Week 3_Lecture 1_Population and Community Ecology_Environmental Science

POPULATION & COMMUNITY ECOLOGY

• Connections among species within communities and the dynamics of individual populations.

Ecology Overview

• Definition: Study of the interactions between organisms and their environment and the balance in these relationships (British Ecological Society).

Biological Organization

• Levels of Organization:

  • Individual: A single organism.

  • Organism: Applies to the individual.

  • Population: A group of organisms of the same species in a given area.

  • Community: All the different populations that live together in an area.

  • Ecosystem: The community and its physical environment.

  • Biosphere: The global sum of all ecosystems, also known as the zone of life on Earth.

Factors to Consider When Studying Population

• Range: Geographic area where a population or species lives.

• Habitat: Specific area where a species finds all its necessary resources.

  • Determining habitat size can be challenging.

Ecological Niches

• Definition: A species’ use of resources and its role in a community.

  • Components:

    • Habitat use.

    • Consumption of certain foods.

    • Role in energy flow and matter cycling.

    • Interactions with other organisms.

  • Specialists: Narrow ecological niches with specific requirements (e.g., Panda, Karner Blue Butterfly, Tiger Salamander).

  • Generalists: Broad ecological niches; adaptable to various habitats (e.g., Raccoon, Rat, Coyote).

Niche Evolution

• Competitive Exclusion Principle: No two species can coexist if they exploit the same resources; illustrated by experiments with Paramecia species populations.

  • Resource Partitioning: Different species use scarce resources in different ways or times to reduce competition.

Types of Competition

• Intraspecific Competition: Competition within the same species (e.g., schools of fish competing for food).

• Interspecific Competition: Competition between different species (e.g., bats and frogs both consuming insects).

Population Growth Dynamics

• Biotic Potential: The capacity for a population to reproduce.

• Environmental Resistance: Factors that limit population growth.

Factors that Limit Population Growth

• Range of Tolerance: Variability in the physical and chemical environment in which organisms can survive (e.g., temperature, sunlight).

• Limiting Factors: Biotic and abiotic factors that restrict the number of organisms in a population (e.g., food, water, disease).

• Carrying Capacity: The maximum population that an ecosystem can sustain indefinitely; affected by limiting factors.

• Density-dependent Factors: Effects that depend on population density (e.g., space, predators, disease, food).

• Density-independent Factors: Factors that affect populations regardless of density (e.g., natural disasters, temperature extremes).

Patterns of Population Growth

• K-selected species:

  • Characteristics: Stability in population size, ecological specialists, slow reproduction, and long lifespan.

  • Examples: Species like elephants and humans.

• R-selected species:

  • Characteristics: Fluctuating population sizes, ecological generalists, rapid reproduction, and short lifespan.

  • Examples: Most insects and small rodents.

Natural Selection and Species Interactions

• Darwin's Idea of Natural Selection:

  • Observed that populations face predation, disease, and competition, leading to survival of individuals with favorable traits.

  • Over generations, favorable traits accumulate in the population.

Coevolution

• Interdependent evolution of two species interacting, leading to changes in their gene pools (e.g., bats and moths, lions and zebras).

Predator-Prey Interactions

• Relationship where one population benefits at the other’s expense, affecting both populations’ dynamics.

• Types include Plant-herbivore and Herbivore-carnivore.

  • Example: Brown tree snake extirpating various bird species in Guam.

Plant-Herbivore Interactions

• Adaptations of herbivores:

  • Seasonal fat accumulation, migration to food sources, hibernation during scarcity.

• Plant adaptations:

  • Producing enough tissue, developing deterrent chemicals, affecting herbivore physiology.

Organismal Defense Mechanisms

• Mimicry: Resembling an object or species to enhance survival (e.g., not being detected by predators).

• Camouflage Mimicry: Blending in with the environment.

• Eye Spot Mimicry: Features that divert predator attention.

• Müllerian Mimicry: Harmful species share similar warning signals for mutual benefit.

• Batesian Mimicry: Non-harmful species resemble harmful species to deter predators.

Symbiosis

• Living arrangements between two different species that can be beneficial or harmful. Types include:

  • Parasitism: One species benefits at the expense of another (e.g., tapeworms, mosquitoes).

  • Commensalism: One species benefits while the other is neither helped nor harmed (e.g., barnacles on whales).

  • Mutualism: Beneficial interactions for both species (e.g., pollinators and flowering plants).

Foundation Species

• Species that create or preserve habitats for other organisms (e.g., coral reefs, kelp forests).

Keystone Species

• Essential species whose removal causes drastic ecosystem changes (e.g., sea otters, wolves).

Indicator Species

• Species sensitive to environmental changes, used to monitor ecosystem health (e.g., lichens for air quality, amphibians for water quality).

Ecological Succession

• Definition: Process by which species composition and habitat structure change over time.

  • Types:

    • Primary Succession: Colonization of lifeless habitats (e.g., after volcanic eruptions).

    • Secondary Succession: Recolonization after disturbances that do not sterilize the environment (e.g., after forest fires).

Population & Community Ecology

Population and community ecology examines the connections among species within communities and the dynamics of individual populations. Ecology is defined as the study of the interactions between organisms and their environment, focusing on the balance in these relationships (British Ecological Society). The levels of biological organization begin with the individual, which is a single organism, and apply to the organism itself. A population consists of a group of organisms from the same species in a specific area, while a community refers to all the different populations living together in that area. An ecosystem includes the community and its physical environment, culminating in the biosphere, the global sum of all ecosystems, also known as the zone of life on Earth.

When studying population characteristics, it is essential to consider the range, which is the geographic area where a population or species lives, and the habitat, the specific area where a species finds its necessary resources. Determining the size of habitat can be challenging. Ecological niches describe a species’ role in a community and its use of resources, including habitat use, food consumption, role in energy flow, matter cycling, and interactions with other organisms. Species can be classified as specialists, which have narrow ecological niches with specific requirements (e.g., Panda, Karner Blue Butterfly, Tiger Salamander), or as generalists, which have broad ecological niches and are adaptable to various habitats (e.g., Raccoon, Rat, Coyote).

Niche evolution can be understood through principles like competitive exclusion, which states that no two species can coexist if they exploit the same resources, illustrated through experiments with Paramecia species populations. In contrast, resource partitioning allows different species to utilize scarce resources in unique ways or during different times, thereby reducing competition. Competition can occur intraspecifically (within the same species, such as schools of fish competing for food) or interspecifically (between different species, such as bats and frogs both consuming insects).

Population growth dynamics are influenced by biotic potential, the capacity for a population to reproduce, and environmental resistance, which consists of the factors that limit this growth. Various factors affect population growth, including the range of tolerance, which indicates the variability in physical and chemical environments that organisms can survive (e.g., temperature, sunlight), as well as limiting factors like food, water, and disease. The carrying capacity refers to the maximum population an ecosystem can sustain indefinitely, subject to limiting factors. Density-dependent factors affect populations based on density (e.g., space, predators, disease, food), while density-independent factors impact populations regardless of density (e.g., natural disasters, temperature extremes).

Patterns of population growth can be categorized into K-selected and R-selected species; K-selected species are characterized by stability in population size, ecological specialists, slow reproduction, and long lifespan (e.g., elephants, humans), whereas R-selected species exhibit fluctuating population sizes, ecological generalists, rapid reproduction, and a short lifespan (e.g., most insects, small rodents). Darwin's idea of natural selection posited that populations face predation, disease, and competition, which leads to the survival of individuals with favorable traits that accumulate over generations.

Coevolution describes the interdependent evolution of two interacting species, affecting both gene pools (e.g., bats and moths, lions and zebras). Predator-prey interactions illustrate relationships where one population benefits at the cost of the other, impacting the dynamics of both populations. These interactions can be seen in types such as plant-herbivore and herbivore-carnivore interactions; for instance, the brown tree snake has extirpated various bird species in Guam.

In terms of plant-herbivore dynamics, herbivores may adapt through seasonal fat accumulation, migration to food sources, or hibernation during scarcity. Plants have their own adaptations, including producing sufficient tissue, developing deterrent chemicals, and affecting herbivore physiology. Organismal defense mechanisms encompass mimicry, wherein species resemble objects or other species for survival. Types of mimicry include camouflage mimicry, where an organism blends in with its environment; eye spot mimicry, which diverts predator attention; Müllerian mimicry, where harmful species share similar warning signals for mutual benefit; and Batesian mimicry, in which non-harmful species resemble harmful ones to deter predators.

Symbiosis refers to the living arrangements between different species, which can be beneficial or harmful. The types of symbiosis include parasitism (one species benefits at the expense of another, e.g., tapeworms, mosquitoes), commensalism (one species benefits while the other is unaffected, e.g., barnacles on whales), and mutualism (beneficial interactions for both species, e.g., pollinators and flowering plants).

Foundation species create or preserve habitats for other organisms (e.g., coral reefs, kelp forests), whereas keystone species are essential in their roles, and their removal leads to significant ecosystem changes (e.g., sea otters, wolves). Indicator species are sensitive to environmental changes and are used to monitor ecosystem health (e.g., lichens indicating air quality, amphibians indicating water quality). Finally, ecological succession is the process by which species composition and habitat structure change over time, categorized into primary succession (the colonization of lifeless habitats, e.g., after volcanic eruptions) and secondary succession (the recolonization following disturbances that do not sterilize the environment, e.g., after forest fires).