Ecology Exam 2

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57 Terms

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Population

A collective group of individuals belonging to the same species that reside in a specific geographic area. For example, gray wolves in Yellowstone National Park interacts with its environment and other species within that ecosystem.

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Dynamic Nature of Populations

  • subject to change in size, structure, and distribution over time due to factors such as birth rates (the number of births in a population), death rates (the number of deaths), immigration (individuals moving into a population), and emigration (individuals leaving a population).

  • For instance, the population of deer may increase during years of abundant food and decrease during harsh winters.

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Demography

The statistical study of populations focusing on size, structure, and distribution at given times. Demographers analyze data like age distributions and sex ratios to understand trends. For example, a study might show that a certain city has a growing population of young adults.

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Dispersal

The process by which individuals move from their birth sites to their breeding sites or among different breeding sites, influencing population structure. For example, young salmon may disperse from freshwater rivers to the ocean as part of their life cycle.

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Abundance

The total number of individuals of a species present in a specific ecosystem at a given time. For instance, a study of a forest may find an _____ of 500 oak trees in a 10-acre area.

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Density

Quantifies the number of individuals existing per unit area or volume. For example, a forest may have a density of 200 trees per acre, which can affect competition for sunlight and nutrients.

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Random Dispersion

A distribution pattern where individuals are distributed without apparent pattern, and each individual has an equal chance of being found anywhere. An example is a population of dandelions in a field that grow in seemingly random locations.

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Regular Dispersion

A distribution pattern where individuals are spaced evenly due to territoriality or limited resources. An example is penguins nesting with equal spacing to reduce competition.

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Clumped Dispersion

A pattern where individuals are concentrated in specific locations, often due to resource availability or social behavior. For instance, schools of fish often gather in groups to enhance protection from predators.

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Variance

A statistical measure that quantifies the degree of variability or spread in a dataset relative to the mean. For example, a variance analysis on fish sizes in a lake can reveal whether the sizes are consistently similar or widely different.

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Area-Based Sampling

A method of surveying individuals within a defined area or volume to estimate population size and distribution. For example, researchers might survey a 1-hectare plot in a forest to estimate the total number of bird species present.

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Line Transects

A technique for counting individuals along a straight line in a designated habitat to estimate population density. For instance, ecologists might use line transects to assess the number of plants in different vegetation zones.

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Mark-Recapture Studies

An ecological method for estimating population sizes; it involves capturing, marking, releasing, and recapturing individuals to assess the population size. For example, scientists may capture a sample of turtles, mark them, and then determine population size by capturing again.

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Exponential Growth

  • Population growth occurring rapidly under optimal environmental conditions, represented mathematically as N(t) = N_0 e^{rt}, where N(t) is the future population size, N_0 is the initial population size, r is the growth rate, and t is time. This growth can be seen in bacteria populating a nutrient-rich agar dish.

  • population increase that occurs continuously at a constant percentage rate. It results in rapid increases in population size when resources are abundant. Unlike geometric growth, exponential growth does not consider environmental limitations. For instance, bacteria can exponentially grow in a nutrient-rich environment until resources are depleted.

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Geometric Growth

  • Population growth occurring at specific intervals characterized by a constant growth rate, modeled as N(t) = N_0 × λ^t. An example is a rabbit population that reproduces seasonally, leading to distinct increases in population each breeding period.

  • type of population increase that occurs at discrete intervals, characterized by a constant growth rate. This leads to a series of population sizes that can be modeled mathematically as a geometric progression. For example, in seasonal breeders like certain fish, the population may double each breeding season under optimal conditions.

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Carrying Capacity (K)

The maximum sustainable population size that an environment can support without degradation. For instance, a lake may have a carrying capacity of 1,000 fish based on its resources.

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Density-Dependent Factors

affecting population growth rates that are based on population density, such as competition for resources and predation. For example, as a population of moose increases, competition for food like lichens can limit further growth.

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Density-Independent Factors

  • Environmental influences that affect population size regardless of population density, such as natural disasters or climate changes. For instance, a hurricane may wipe out a coastal bird population irrespective of its size.

  • As more individuals inhabit an area, struggles for resources can limit reproduction and increase mortality rates. For instance, in a crowded deer population, limited food resources can lead to reduced female reproductive rates.

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Type I Survivorship Curve

This curve represents species with high survival rates during early and middle life and significant drop-offs in older age. Humans exhibit a this curve, where most individuals survive to old age.

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Cohort Life Table

A dynamic tool tracking a specific group of individuals from birth through death over time, providing insights into population dynamics. For example, could be created for a group of sea turtles, showing survival rates at various life stages.

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Competitive Exclusion Principle

This principle states that two species competing for the same limited resources cannot coexist indefinitely. An example is two species of barnacles competing for space on a rock, where one may outcompete the other.

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Asymmetrical Competition

A type of competition where one species significantly negatively impacts another much more than vice versa, potentially leading to exclusion. For instance, when a dominant plant species crowds out a weaker species in a forest.

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What is Logistic Population Growth?

population growth starts with an initial exponential growth phase followed by a slowdown as the population reaches the carrying capacity (K) of its environment. For example, a rabbit population may grow rapidly until food and space limit further increases, stabilizing around K.

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How does age and size structure influence population growth?

The age and size structure of a population significantly affects its growth potential. Younger individuals typically have higher reproductive rates, thereby contributing more to population growth. In contrast, older individuals may have lower birth rates and higher risks of mortality. For instance, a population with many juveniles can increase rapidly while a population predominantly composed of older individuals may decline if not replaced effectively.

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What are the three types of Survivorship Curves?

Survivorship curves depict mortality rates in populations:

  • Type I: High survival in early life, with significant mortality in older age (e.g., humans, elephants).

  • Type II: Constant mortality rate throughout life (e.g., birds, some reptiles).

  • Type III: High juvenile mortality rate, with survivors living longer (e.g., fish, amphibians). Differences arise from varying reproductive strategies and environmental influences.

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Cohort and Static Life Table?

  • one tracks a specific group of individuals born at the same time throughout their lives, allowing for detailed observation of mortality and reproduction rates over time.

  • the other table provides a snapshot of a population's age distribution at a specific time, using various aged individuals to estimate life expectancy and survival rates.

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What does K represent in the Logistic Growth Model?

signifies the maximum population size that an environment can sustainably support indefinitely without degrading its habitat. Populations at K do not necessarily stay static; they may fluctuate around this value due to environmental changes, resource availability, and interspecies interactions.

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What does a Population Pyramid show?

Represents the age and sex distribution of a population, providing insights into birth rates, death rates, and overall population growth trends. Analyzing its shape helps indicate whether a population is growing, stable, or declining, allowing predictions about future demographic changes.

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What factors contribute to smaller organisms having higher r values?

  • shorter lifespans facilitate more frequent reproduction; they typically produce larger numbers of offspring per breeding event; and they can quickly exploit available resources.

  • Additionally, tend to reach sexual maturity at an earlier age, further enhancing their reproductive potential.

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What does λ = 1 indicate?

population is stable; the number of individuals remains constant over time because births and deaths are equal. Conversely, when λ < 1, the population is declining since deaths outnumber births, leading to a decrease in overall population size.

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What are some assumptions of Exponential Growth?

  1. The population grows in an ideal environment with unlimited resources.

  2. Individuals are identical in their chances of survival and reproduction.

  3. There are no immigration or emigration effects influencing the population size.

  4. The growth rate remains constant over time, irrespective of population density.

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What is an Inflection Point?

signifies where the curvature changes direction, indicating a shift in the growth rate of the population. It marks the transition from accelerating growth to decelerating growth as resources become limited.

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Define Resource

any substance or factor that organisms consume, which supports population growth when available.

  • are effectively utilized for survival and reproduction.

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Explain Conditions

environmental influences that affect growth and survival, but unlike resources, they are not consumed. Examples include temperature, humidity, and light.

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Explain Exploitation Competition

occurs when individuals utilize shared resources, decreasing their availability for others without direct interaction. Each competitor reduces the resource pool through consumption.

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Explain Interference Competition

involves direct and aggressive interactions between individuals, restricting each other's access to resources. This type of competition can lead to physical confrontations or behaviors that block resource access.

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Define Temporal Variation in Competition

how competitive interactions change over time due to shifts in resource availability, population densities, and seasonal conditions that affect competitive environments.

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Define Spatial Variation in Competition

how competitive interactions differ across different locations, influenced by localized resource distribution and environmental factors.

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Define Fundamental Niche

full range of environmental conditions and resources a species could utilize in the absence of competition, representing the ideal conditions for survival and reproduction.

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Define Realized Niche

actual conditions and resources a species uses, shaped by competition and other ecological interactions. It is generally smaller than the fundamental niche.

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Explain the Competitive Exclusion Principle

two species competing for the same limited resources cannot coexist indefinitely. Coexistence happens through niche differentiation or temporal resource utilization.

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Define Niche Partitioning

process where species reduce competition by utilizing different resources or exploiting the same resources at different times, allowing for coexistence.

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Define Character Displacement

evolutionary changes in species' traits that reduce competition, often resulting from niche partitioning. Over time, species evolve to exploit different resources more effectively.

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Describe Type I Response in Predator Functional Response

characterized by a linear increase in predation with increasing prey density; it is common in filter feeders, where predation rate does not saturate.

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Describe Type II Response in Predator Functional Response

while predation increases with prey density, it eventually levels off due to handling time and the limits to how fast predators can consume prey.

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Describe Type III Response in Predator Functional Response

low predation rates at low prey densities, increased predation at moderate densities, and a plateau at high densities due to resource limitation and handling time.

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Why are Parasites Specialists?

are able to adapt to efficiently exploit specific host species, which enhances their survival and reproductive success by focusing their energy and strategies on a limited set of suitable hosts.

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How do Behavior-Altering Parasites Facilitate Transmission?

modify their host's behavior to enhance their transmission to new hosts, sometimes increasing the risk of predation for their host, which ensures the parasite’s lifecycle continues.

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Effects Beyond Mortality from Predators and Parasites

causing stress responses that can alter growth rates and reproduction, impacting overall population dynamics.

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How can a Predator Create a Trophic Cascade?

By controlling herbivore populations, which in turn influences vegetation dynamics and the overall health of the ecosystem by affecting resource availability.

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Components of Lotka-Volterra Predator-Prey Models

showing how prey populations grow based on reproduction and decline due to predation, resulting in oscillating dynamics where both populations influence each other.

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Lotka-Volterra Competition Model Components

dN1/dt = r1N1(1 - (N1 + αN2)/K1) for species 1 and dN2/dt = r2N2(1 - (N2 + βN1)/K2) for species 2, where α and β are coefficients indicating competitive effects.

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Predator Presence and Competition Outcomes

reducing the populations of dominant competitors, allowing subordinate species to thrive and coexist in the habitat.

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Disturbances and Coexistence

can reset competitive hierarchies, enabling coexistence between highly asymmetrical competitors by providing opportunities for less competitive species to establish and flourish.

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Barnacle Competition Dynamics

In Balanus versus Chthamalus competition, Balanus has a broader fundamental niche, but Chthamalus occupies higher intertidal zones where competitive pressure is lower, allowing it to persist.

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Carnivores as Generalists vs. Herbivores as Specialists

  • Carnivores consuming a variety of prey,

  • herbivores tend to specialize on a narrower range of plant species that maximize nutrient absorption and efficient feeding.

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Pros and Cons of Ecto- and Endoparasites

Ectoparasites benefit from easier dispersal but face greater environmental risks, while endoparasites have easier access to nutrients but depend heavily on host survival and face immune responses.