Note
Studied by 11 peopleEcology Exam 2
Population Distribution and Abundance
Population: A population is defined as a collective group of individuals belonging to the same species that reside in a specific geographic area and engage in various interactions. These interactions can involve reproduction, competition for resources, and predation. For instance, in a forest ecosystem, a population of deer interacts with one another through mating, competing for food like grass and leaves, and serving as prey for predators such as wolves.
Dynamic Nature: Populations are inherently dynamic, meaning they are subject to change in size, structure, and distribution over time. Factors that cause these changes include birth rates, death rates, immigration (individuals moving into a population), and emigration (individuals moving out of a population).
Example: The Pacific herring population, studied across the marine environments from 1973 to 2016, shows significant fluctuations in spawning biomass. Such fluctuations can be influenced by environmental conditions like temperature changes, availability of food sources, and fishing pressures from humans.
Geographic Distribution
Populations can be found broadly across many habitats, extending from coastal areas to mountainous regions. For example, the populations of salmon are found in specific rivers across the United States and Canada.
Documented Spawning Grounds: The Southern Salish Sea is known for its diverse aquatic life and notable spawning grounds for various fish species, such as salmon and herring. This example illustrates the significance of localized habitats for sustaining historical fish populations, promoting biodiversity, and aiding in the recovery of endangered species.
Demography - The Study of Populations
Key Concepts in Demography
Demography: Demography is the statistical study of populations, focusing on aspects such as their size, structure, and distribution at given times. Key components of demography include:
Dispersal: The process by which individuals move from their birth sites to their breeding sites or among different breeding sites. This is distinct from migration, which often involves regular seasonal movement. For instance, young sea turtles exhibit dispersal by moving from beaches to offshore feeding areas often kilometers away.
Distribution: The specific geographic area where a species occurs. For example, the northern spotted owl has a distribution concentrated in old-growth forests of the Pacific Northwest, as indicated by various ecological studies that mapped their habitats.
Abundance and Density:
Abundance: This term refers to the total number of individuals of a species present in a specific ecosystem at a given time. A greater abundance of a species, such as rabbits in an area, indicates successful reproduction and resource availability.
Density: Density quantifies how many individuals exist per unit area or volume. For example, a densely populated area of trees may host 200 trees per acre, while a sparsely populated area might only have 50 trees per acre.
Spatial Arrangements in Populations
Dispersion Patterns
Population dispersion patterns are influenced by resource availability, individual behavior, competition, and environmental conditions. The three primary types of dispersion patterns include:
Random Dispersion: In this pattern, individuals are distributed with no apparent pattern and each individual has an equal chance of being found anywhere. This may occur in areas where resources are abundant and evenly distributed, like dandelions growing randomly across a field.
Regular Dispersion: Individuals are spaced evenly due to territoriality or limited resources, leading to a more uniform distribution. For example, penguins often exhibit regular spacing when nesting to reduce competition for space and food.
Clumped Dispersion: When individuals are concentrated in specific locations, often due to resource availability or social behavior. For instance, schools of fish tend to cluster together in areas of high food availability, leading to a clumped distribution pattern.
Variability in Population Metrics
Understanding population metrics hinges on analyzing central statistics, such as means and variance:
Mean: The mean signifies the average value derived from a set of population observations. For example, if 5 sample plots have tree counts of 10, 15, 20, 25, and 30, the mean tree density is 20 trees per plot.
Variance: Variance assesses the degree of variability or spread within the population data. If plots have tree counts of 5, 20, and 35 trees, the variance will indicate how spread out the counts are from the calculated mean.
Classification Based on Variance: Populations can also be classified based on the relationship between variance and mean:
Clumped: When variance is greater than the mean, indicating clusters of high abundance and areas with fewer individuals. For example, grasshoppers might cluster in a few rich patches of grass, leading to greater local density in specific areas.
Random: Variance equals the mean; this suggests a uniform population distribution across the area, typical in habitats with evenly distributed resources.
Regular: Variance is less than the mean, suggesting low variability and consistent spacing, often observed in territorial species like various bird species that maintain distance from each other.
Methods for Estimating Population Characteristics
Area-Based Sampling: This standard approach involves surveying individuals within a defined area or volume to estimate population size and distribution. It is commonly used in ecological studies for stationary organisms like plants. For example, counting all the flowering plants in a one-acre plot could yield insights into species abundance.
Line Transects: In this method, observers travel along a straight line in a designated habitat, counting individuals and measuring their distances from the line to account for potential biases in visibility. For instance, researchers may count birds within 50 meters of a transect line, allowing them to adjust for detection probabilities more accurately.
Mark-Recapture Studies: This method is particularly useful for populations of mobile organisms and involves three main steps:
Capture: A known number of individuals are captured, marked for identification, and recorded.
Release: The marked individuals are then released back into their environment to mix with the unmarked population.
Recapture: After some time, researchers recapture individuals to estimate total population size based on the ratio of marked to unmarked individuals.
Example Calculation: If 428 rats are initially marked and later, during the second capture, 380 rats are caught with 3 of them already marked, the population estimate (N) can be computed using the formula: N = (428 x 380) / 3. This formula helps to derive a more accurate total count of the population, aiding in ecological management practices.
Population Growth and Regulation
Population Dynamics
Temporal patterns in populations
Logistic growth
Variable fluctuations
K is population size where birth rate = death rate
The birth and death rates do not vary at a given density so they intersect at K, the carrying capacity.
A real population will look similar but the lines would be significantly bigger showing a greater overlap resulting in multiple points of K
Outbreaks
Population outbreaks have negative impact on environment
Bugs, jellyfish
Regular cycles
Consistent cycles in population abundance
Populations that cycle undergo delayed density dependence - populations density in the past affects its future growth or survival
Can cause fluctuation and time lags - requires negative feedback mechanism (predation)
Oscillations
Induced defenses and predation cause oscillations in populations
Extinction in small populations
Effect of population size on extinction risk
The risk of extinction increases greatly in small populations
Fluctuations can be highly problematic for smaller populations that have less to lose
Primary factors underlying local extinction
Demographic stochasticity: the quality of lacking any predictable order or plan
Chance variation in individual birth and death
Chance variation in sex ratios
Random fluctuations in population size occur because the birth and death of each individual is a discrete and probabilistic event
Environmental stochasticity
Effect of random environmental fluctuations on growth rate in population
Genetic problems
Inbreeding depression
Genetic drift
Loss of heterozygosity
Behavioral problems
Allee Effects: Lamda or r decreases with an increase in population size
Extinction Vortex
Population Distribution and Abundance
Definition of Population:
A population is defined as a group of individuals belonging to the same species, inhabiting a specific area at a given time. This definition reflects the biological and ecological interactions of these individuals, which may include sexual reproduction, competition for resources, and predatory relations within their environment.
Dynamic Nature of Populations:
Populations are not static; they are dynamic entities that experience fluctuations in size and distribution over time and across different geographies.
For example, studies of the Pacific herring population from 1973-2016 in the Southern Salish Sea have revealed significant variability in population size. Key locations observed include:
San Juan Islands
Squaxin Island
Cherry Point
Other significant estuarine and coastal areas in Canada and the United States.
Population dynamics for Pacific herring are measured in metric tonnes, focusing on cumulative spawning biomass estimates derived from various genetic groups, informing conservation efforts and fisheries management.
Key Demographic Concepts:
Demography: The statistical study of populations, encompassing the examination of structures, patterns, and changes over time, which is crucial for understanding the ecology and management of species.
Dispersal: Refers to the movement of individuals from their birthplace or breeding grounds to new locations, a process integral to population dynamics and genetic diversity, distinct from seasonal migration.
Distribution: Refers to the geographic regions where individuals of a species are found; crucial for studying habitat preferences and ecological niches.
Observations on Species Distribution:
The American crow is a case study in species distribution, showcasing how a species can be widely distributed yet exhibit higher concentrations in specific 'hot spots.' This distribution has been assessed using comprehensive long-term data from the Audubon Christmas Bird Count, which was initiated in 1900, allowing researchers to track population trends and habitat changes over time.
Understanding Abundance and Density:
Abundance refers to the total number of individuals of a species within a specific area, an essential measure for assessing ecosystem health.
Density provides a nuanced view of abundance by quantifying it per unit area or volume, enabling ecologists to evaluate population pressure and habitat suitability.
Dispersion Patterns in Populations:
Dispersion describes the spatial arrangement of individuals within a habitat, influenced by key ecological factors such as:
The availability and distribution of resources.
Intraspecies competition, behavioral interactions, and dispersal strategies.
Types of Dispersion Patterns Include:
Random Dispersion: Individuals are distributed without a defined pattern, having an equal probability of occurring anywhere.
Regular Dispersion: Individuals are evenly spaced across the environment, potentially due to territorial behavior.
Clumped Dispersion: Individuals are grouped in clusters, often in areas of high resource availability, reflecting social behavior or resource clumping.
Statistical Measures in Demography:
Mean: Represents the average value within a dataset, determined by the sum of observations divided by their total count, a basis for comparative analysis.
Variance: A measure that quantifies the degree of variability or spread in a dataset relative to the mean, informing our understanding of population stability.
The relationship between variance and mean can help categorize population distributions into three main types:
Clumped Distribution: Variance is greater than the mean, indicating high variability in individual positions.
Random Distribution: Variance is equal to the mean, suggesting that individuals are dispersed independently.
Regular Distribution: Variance is less than the mean, indicating a more uniform spacing of individuals in the habitat.
Individual Definition in Populations:
An individual organism can be precisely defined as the product of a single fertilization, forming a distinct genetic unit; however, in certain plant species like aspen, which can produce genetically identical clones known as a "genet," the term may refer to a group of such clones, with physiologically independent members termed "ramets" (e.g., strawberries).
Estimating Population Abundances and Distributions:
Effective approaches to estimate population sizes and distributions include:
Area-based counts: Involves counting individuals within a defined area or volume, providing total counts for specific habitats.
Line transects: This technique involves counting individuals along a predetermined linear pathway and estimating distances to individuals away from the line, yielding population density estimates.
Mark-recapture studies: A critical method for estimating population sizes wherein individuals are captured, marked, and released, with follow-up captures used to gauge the proportion of marked individuals in subsequent populations.
Example Calculation in Mark-Recapture Studies:
The total population size can be estimated using the formula:
N = (M x C) / R, where:
N = estimated total population size.
M = number of marked individuals in the initial sample.
C = total number of individuals captured in the second sample.
R = number of marked individuals that were recaptured.
For instance, if 428 rats were initially marked, and in a subsequent capture, 380 were caught with 3 of those marked, the total population can be roughly estimated, facilitating further research and management practices.
Population Distribution and Abundance
Definition of Population:
A population is defined as a group of individuals belonging to the same species, inhabiting a specific area at a given time. This definition reflects the biological and ecological interactions of these individuals, which may include sexual reproduction, competition for resources, and predatory relations within their environment.
Dynamic Nature of Populations:
Populations are not static; they are dynamic entities that experience fluctuations in size and distribution over time and across different geographies.
For example, studies of the Pacific herring population from 1973-2016 in the Southern Salish Sea have revealed significant variability in population size. Key locations observed include:
San Juan Islands
Squaxin Island
Cherry Point
Other significant estuarine and coastal areas in Canada and the United States.
Population dynamics for Pacific herring are measured in metric tonnes, focusing on cumulative spawning biomass estimates derived from various genetic groups, informing conservation efforts and fisheries management.
Key Demographic Concepts:
Demography: The statistical study of populations, encompassing the examination of structures, patterns, and changes over time, which is crucial for understanding the ecology and management of species.
Dispersal: Refers to the movement of individuals from their birthplace or breeding grounds to new locations, a process integral to population dynamics and genetic diversity, distinct from seasonal migration.
Distribution: Refers to the geographic regions where individuals of a species are found; crucial for studying habitat preferences and ecological niches.
Observations on Species Distribution:
The American crow is a case study in species distribution, showcasing how a species can be widely distributed yet exhibit higher concentrations in specific 'hot spots.' This distribution has been assessed using comprehensive long-term data from the Audubon Christmas Bird Count, which was initiated in 1900, allowing researchers to track population trends and habitat changes over time.
Understanding Abundance and Density:
Abundance refers to the total number of individuals of a species within a specific area, an essential measure for assessing ecosystem health.
Density provides a nuanced view of abundance by quantifying it per unit area or volume, enabling ecologists to evaluate population pressure and habitat suitability.
Dispersion Patterns in Populations:
Dispersion describes the spatial arrangement of individuals within a habitat, influenced by key ecological factors such as:
The availability and distribution of resources.
Intraspecies competition, behavioral interactions, and dispersal strategies.
Types of Dispersion Patterns Include:
Random Dispersion: Individuals are distributed without a defined pattern, having an equal probability of occurring anywhere.
Regular Dispersion: Individuals are evenly spaced across the environment, potentially due to territorial behavior.
Clumped Dispersion: Individuals are grouped in clusters, often in areas of high resource availability, reflecting social behavior or resource clumping.
Statistical Measures in Demography:
Mean: Represents the average value within a dataset, determined by the sum of observations divided by their total count, a basis for comparative analysis.
Variance: A measure that quantifies the degree of variability or spread in a dataset relative to the mean, informing our understanding of population stability.
The relationship between variance and mean can help categorize population distributions into three main types:
Clumped Distribution: Variance is greater than the mean, indicating high variability in individual positions.
Random Distribution: Variance is equal to the mean, suggesting that individuals are dispersed independently.
Regular Distribution: Variance is less than the mean, indicating a more uniform spacing of individuals in the habitat.
Individual Definition in Populations:
An individual organism can be precisely defined as the product of a single fertilization, forming a distinct genetic unit; however, in certain plant species like aspen, which can produce genetically identical clones known as a "genet," the term may refer to a group of such clones, with physiologically independent members termed "ramets" (e.g., strawberries).
Estimating Population Abundances and Distributions:
Effective approaches to estimate population sizes and distributions include:
Area-based counts: Involves counting individuals within a defined area or volume, providing total counts for specific habitats.
Line transects: This technique involves counting individuals along a predetermined linear pathway and estimating distances to individuals away from the line, yielding population density estimates.
Mark-recapture studies: A critical method for estimating population sizes wherein individuals are captured, marked, and released, with follow-up captures used to gauge the proportion of marked individuals in subsequent populations.
Example Calculation in Mark-Recapture Studies:
The total population size can be estimated using the formula:
N = (M x C) / R, where:
N = estimated total population size.
M = number of marked individuals in the initial sample.
C = total number of individuals captured in the second sample.
R = number of marked individuals that were recaptured.
For instance, if 428 rats were initially marked, and in a subsequent capture, 380 were caught with 3 of those marked, the total population can be roughly estimated, facilitating further research and management practices.
Definition of Population
Population: A population is defined as a collective group of individuals belonging to the same species that reside in a specific geographic area and engage in various interactions. These interactions can involve reproduction, competition for resources, and predation. For instance, in a forest ecosystem, a population of deer interacts with one another through mating, competing for food like grass and leaves, and serving as prey for predators such as wolves.
Characteristics of Populations
Dynamics of Populations
Dynamic Nature: Populations are inherently dynamic, meaning they are subject to change in size, structure, and distribution over time. Factors that cause these changes include birth rates, death rates, immigration (individuals moving into a population), and emigration (individuals moving out of a population).
Example: The Pacific herring population, studied across the marine environments from 1973 to 2016, shows significant fluctuations in spawning biomass. Such fluctuations can be influenced by environmental conditions like temperature changes, availability of food sources, and fishing pressures from humans.
Geographic Distribution
Populations can be found broadly across many habitats, extending from coastal areas to mountainous regions. For example, the populations of salmon are found in specific rivers across the United States and Canada.
Documented Spawning Grounds: The Southern Salish Sea is known for its diverse aquatic life and notable spawning grounds for various fish species, such as salmon and herring. This example illustrates the significance of localized habitats for sustaining historical fish populations, promoting biodiversity, and aiding in the recovery of endangered species.
Demography - The Study of Populations
Key Concepts in Demography
Demography: Demography is the statistical study of populations, focusing on aspects such as their size, structure, and distribution at given times. Key components of demography include:
Dispersal: The process by which individuals move from their birth sites to their breeding sites or among different breeding sites. This is distinct from migration, which often involves regular seasonal movement. For instance, young sea turtles exhibit dispersal by moving from beaches to offshore feeding areas often kilometers away.
Distribution: The specific geographic area where a species occurs. For example, the northern spotted owl has a distribution concentrated in old-growth forests of the Pacific Northwest, as indicated by various ecological studies that mapped their habitats.
Abundance and Density:
Abundance: This term refers to the total number of individuals of a species present in a specific ecosystem at a given time. A greater abundance of a species, such as rabbits in an area, indicates successful reproduction and resource availability.
Density: Density quantifies how many individuals exist per unit area or volume. For example, a densely populated area of trees may host 200 trees per acre, while a sparsely populated area might only have 50 trees per acre.
Spatial Arrangements in Populations
Dispersion Patterns
Population dispersion patterns are influenced by resource availability, individual behavior, competition, and environmental conditions. The three primary types of dispersion patterns include:
Random Dispersion: In this pattern, individuals are distributed with no apparent pattern and each individual has an equal chance of being found anywhere. This may occur in areas where resources are abundant and evenly distributed, like dandelions growing randomly across a field.
Regular Dispersion: Individuals are spaced evenly due to territoriality or limited resources, leading to a more uniform distribution. For example, penguins often exhibit regular spacing when nesting to reduce competition for space and food.
Clumped Dispersion: When individuals are concentrated in specific locations, often due to resource availability or social behavior. For instance, schools of fish tend to cluster together in areas of high food availability, leading to a clumped distribution pattern.
Variability in Population Metrics
Understanding population metrics hinges on analyzing central statistics, such as means and variance:
Mean: The mean signifies the average value derived from a set of population observations. For example, if 5 sample plots have tree counts of 10, 15, 20, 25, and 30, the mean tree density is 20 trees per plot.
Variance: Variance assesses the degree of variability or spread within the population data. If plots have tree counts of 5, 20, and 35 trees, the variance will indicate how spread out the counts are from the calculated mean.
Classification Based on Variance
Populations can also be classified based on the relationship between variance and mean:
Clumped: When variance is greater than the mean, indicating clusters of high abundance and areas with fewer individuals. For example, grasshoppers might cluster in a few rich patches of grass, leading to greater local density in specific areas.
Random: Variance equals the mean; this suggests a uniform population distribution across the area, typical in habitats with evenly distributed resources.
Regular: Variance is less than the mean, suggesting low variability and consistent spacing, often observed in territorial species like various bird species that maintain distance from each other.
Methods for Estimating Population Characteristics
Area-Based Counts
Area-Based Sampling: This standard approach involves surveying individuals within a defined area or volume to estimate population size and distribution. It is commonly used in ecological studies for stationary organisms like plants. For example, counting all the flowering plants in a one-acre plot could yield insights into species abundance.
Line Transects
In this method, observers travel along a straight line in a designated habitat, counting individuals and measuring their distances from the line to account for potential biases in visibility. For instance, researchers may count birds within 50 meters of a transect line, allowing them to adjust for detection probabilities more accurately.
Mark-Recapture Studies
This method is particularly useful for populations of mobile organisms and involves three main steps:
Capture: A known number of individuals are captured, marked for identification, and recorded.
Release: The marked individuals are then released back into their environment to mix with the unmarked population.
Recapture: After some time, researchers recapture individuals to estimate total population size based on the ratio of marked to unmarked individuals.
Example Calculation: If 428 rats are initially marked and later, during the second capture, 380 rats are caught with 3 of them already marked, the population estimate (N) can be computed using the formula: N = (428 x 380) / 3. This formula helps to derive a more accurate total count of the population, aiding in ecological management practices.
Introduction
Population growth refers to the increase in the number of individuals within a specific population over a designated time frame. Understanding the dynamics of population growth is crucial for various fields, including ecology, conservation biology, and resource management.
Types of Population Growth
Exponential Growth:This type of growth occurs when populations increase rapidly due to optimal environmental conditions. For example, if a group of bacteria is placed in a nutrient-rich environment, they may multiply rapidly in a short period, leading to a dramatic increase in their numbers. This growth can continue unchecked until resources become limited. Exponential growth is mathematically represented as: [ N(t) = N_0 e^{rt} ]Where:
N(t): Population size at time t.
N_0: Initial population size.
r: Intrinsic growth rate.
Geometric Growth:This occurs at specific intervals, especially in species with distinct breeding seasons. For instance, if a breed of fish lays eggs once a year, their population may increase exponentially during that period if conditions are ideal. The equation for geometric growth is:[ N(t) = N_0 \cdot \lambda^t ]Where:
λ (lambda): Growth rate per time interval; values greater than 1 indicate growth, while values less than 1 indicate decline.
Age Structure
Age Structure:This concept refers to the distribution of individuals of different ages within a population. It is often depicted in population pyramids, which show the proportion of the population at each age. Understanding age structure helps predict future growth rates and demographic changes.
Age-Specific Survivorship and Fecundity:These measures indicate the probability of survival (survivorship) and reproductive output (fecundity) for different ages. For instance, a life table might show that juveniles of a species have a 90% survival rate to age one, while adults have a survival rate of 70%. In such a case, those juvenile individuals will not contribute as much to the population's growth compared to older, reproducing individuals.
Population Growth Rate
Growth Rate:This is defined as the difference between the number of new individuals produced and the number of individuals that die during a given period. It can be affected by immigration (influx of new individuals) and emigration (outflux of individuals from a population). The growth rate can be expressed mathematically as: [ ext{Growth Rate} = \frac{(B + I) - (D + E)}{N} ]Where:
B: Number of births.
D: Number of deaths.
I: Immigration.
E: Emigration.
Population Size Variables
N: Represents the total population size.
Nt: Refers to the population size at a specific point in time.
Population Growth Calculation:The fundamental formula for calculating future population size (Nt+1) is: [ N_{t+1} = N_t + B - D + I - E ]Where:
B: Births.
D: Deaths.
I: Immigration.
E: Emigration.
Continuous Growth Model
This model assumes that population growth occurs continuously over time rather than in discrete intervals. It can be modeled using differential equations, which provide more precise insights into population dynamics. Factors influencing continuous growth include the current population size and the birth rates.
Differential Equations in Population Dynamics
Change in Population Size:The change in the population size over an infinitesimal time interval is represented by ( \frac{dN}{dt} ).
Birth Rate Equation:The equation ( B = bN ) illustrates that the number of births (B) equals the instantaneous birth rate (b) multiplied by the current population size (N).
Intrinsic Rate of Change (r):This represents the potential growth rate of a population and is calculated as the difference between birth and death rates (b - d). It’s crucial in determining how rapidly a population can grow under given conditions.
Exponential Growth Equation
The exponential growth model can be expressed as: [ N_{t+1} = N_0 e^{rt} ]Where:
N_0: Initial population size.
r: Intrinsic growth rate.
t: Time period.Example Calculation:If you start with an initial population of 100 individuals (N0) and an intrinsic growth rate (r) of 0.1, then after one day (t = 1):( dN/dt = rN = (0.1)(100) = 10 )This results in a new population size of 110 individuals after one day.
Characteristics of Exponential Growth
Rapid Increases: Under optimal conditions, species like rats can increase their populations from 25 to 304 individuals in just 100 days.
Influence of Life History Traits: Smaller organisms often display higher growth rates because of shorter life cycles and faster maturation compared to larger species.
Geometric Growth
Constant Growth Rates:This growth model is characterized by a constant growth rate over discrete time intervals, particularly in species with non-overlapping generations or defined breeding seasons.
Geometric Growth Example:For example, a species of tree that grows by a fixed percentage annually would demonstrate geometric growth.
Geometric Growth Equations:
Nt+1 = Nt x λ
λ (lambda): Growth rate parameter; if λ > 1, the population increases, while λ < 1 indicates a decrease.
Population Age Distributions
Age distributions within a population can significantly influence future growth patterns. For instance, a population with a high proportion of older individuals may face declines, while one with many young individuals may expand rapidly. Analyzing these distributions helps in forecasting potential demographic shifts and their socioeconomic impacts.
Survivorship Curves
Survivorship curves depict patterns of mortality among individuals in a population and are classified into three primary types:
Type I:Characterized by high survival rates until old age, typical of species like elephants and humans, where mortality increases significantly in the later stages of life.
Type II:Exhibits a constant mortality rate at all ages, such as many bird species, where survival chances are relatively uniform.
Type III:Characterized by high mortality rates among juveniles, as seen in species like oysters or many fish, which produce a large number of offspring with low chances of survival to adulthood.
Life Tables
Cohort Life Table:This table tracks a specific group of individuals from birth through death, offering valuable insights into the population dynamics of organisms, especially in sessile species like trees.
Static Life Table:Provides a snapshot of survival and reproduction at a single time, important for mobile species or those exhibiting long lifespans.
Factors Affecting Population Growth
Density-Dependent Factors:These factors impact population growth rates based on density, including resource competition (food, space), predator-prey dynamics, and disease spread.
Density-Independent Factors:These factors affect growth irrespective of population density, such as climate variations, natural disasters, or human activities like habitat destruction.
Logistic Growth
S-Shaped Curve:Logistic growth is characterized by an S-shaped curve, where growth acceleration occurs initially, followed by deceleration and stabilization as the population approaches its carrying capacity (K).
Carrying Capacity (K):Defined as the maximum sustainable population size that the environment can support without degradation. When the population size exceeds K, resources become scarce, leading to increased mortality and reduced reproduction
Compare and contrast geometric and exponential growth
Geometric Growth: This type of growth occurs in discrete time intervals, characterized by a constant growth rate, resulting in a series of population sizes that can be modeled as a geometric progression. It is often seen in populations with seasonal breeding.
Exponential Growth: Unlike geometric growth, exponential growth occurs continuously and is characterized by a constant percentage increase over time, leading to a rapid increase in population size when resources are abundant. This model does not account for environmental limitations, unlike logistic growth.
Describe some characteristics of geometric and exponential growth
Geometric Growth:
Occurs in discrete time intervals.
Constant growth rate.
Population sizes follow a geometric progression.
Common in seasonal breeders.
Growth is often limited by resource availability and environmental factors.
Exponential Growth:
Occurs continuously over time.
Characterized by a constant percentage increase.
Leads to rapid population increases under ideal conditions.
Assumes unlimited resources, not accounting for environmental constraints.
Can result in population overshoot and subsequent crashes when resources become limiting.
Define what density-independent factors are, and how they affect population growth rate and population size.
Density-independent factors are environmental influences that affect population size regardless of the population's density, such as natural disasters, climate change, and human activities. These factors can lead to sudden and significant reductions in population size, impacting growth rates by causing fluctuations that are not related to the density of the population. Consequently, populations may experience dramatic declines even when they are not overcrowded, highlighting the importance of considering these factors in ecological studies.
Define what density-dependent factors are, and how they affect population growth rate and population size.
Density-dependent factors are influences on population size that vary with the population density, such as competition for resources, predation, and disease. As population density increases, these factors become more pronounced, leading to a decrease in growth rates and potentially stabilizing the population size. For example, higher densities can result in increased competition for food and space, which can limit reproduction and lead to higher mortality rates. Understanding the interplay between density-dependent and density-independent factors is crucial for comprehending population dynamics in ecological systems.
Define logistic population growth and compare it to exponential growth
Logistic population growth is characterized by an initial period of exponential growth followed by a slowdown as the population reaches the carrying capacity of its environment. Unlike exponential growth, which occurs when resources are unlimited and population increases rapidly, logistic growth takes into account the limitations imposed by resource availability, leading to a more stable population size over time. This model illustrates how populations can grow quickly when conditions are favorable but will eventually stabilize as environmental resistance factors, such as limited food and space, come into play. In contrast, exponential growth can lead to unsustainable population sizes, resulting in potential crashes when resources are depleted.
Describe how age and size structure influences population growth and population size
Age and size structure play a significant role in determining population growth rates and overall population size. Younger individuals typically have higher reproductive rates, contributing more to population growth, while older individuals may have lower reproductive rates and higher mortality. Additionally, the distribution of size classes within a population can affect its resilience and ability to adapt to environmental changes. For example, a population with a high proportion of juvenile individuals may grow rapidly, while a population dominated by older individuals may face declines if they do not replace themselves effectively. Understanding these dynamics is essential for predicting how populations will respond to environmental pressures and resource availability.
Compare the three types of survivorship curves, and list some examples of organisms that fall within each type. Discuss why there are differences within the shapes of these curves within populations.
Type I Survivorship Curve: Characterized by high survival rates during early and middle life, with a significant drop in survivorship in older age. Examples include humans and large mammals like elephants.
Type II Survivorship Curve: Exhibits a constant mortality rate throughout the life span. Organisms such as birds and some reptiles demonstrate this pattern, as they have a relatively stable chance of dying at any age.
Type III Survivorship Curve: Features high mortality rates for the young, but those that survive to adulthood can expect to live much longer. Examples include many fish species and amphibians, which produce large numbers of offspring to offset high juvenile mortality rates.
The differences in the shapes of these curves arise from various reproductive strategies, environmental factors, and life history traits that influence survival and reproduction in different species.
What is the difference between a cohort and static life table?
A cohort life table tracks a group of individuals born at the same time throughout their lives, allowing for the observation of mortality and reproduction rates over time, while a static life table provides a snapshot of the age distribution of a population at a specific time, using data from individuals of various ages to estimate life expectancy and survival rates. In essence, cohort tables are dynamic and follow a specific generation, whereas static tables are more static and provide a cross-sectional view that can be useful for understanding population structure at a given moment.
What is meant by K in the logistic growth model? Do populations that reach K stay static? Why or why not?
K, or carrying capacity, refers to the maximum population size that an environment can sustain indefinitely without degrading the habitat. Populations that reach K do not necessarily remain static; they often fluctuate around this value due to environmental changes, resource availability, and interactions with other species, leading to cycles of growth and decline as the population adjusts to the carrying capacity. These fluctuations can be influenced by factors such as predation, disease, and competition, which can cause temporary increases or decreases in population size, demonstrating the dynamic nature of ecosystems.
What does a population pyramid tell us about a population in ecology?
A population pyramid visually represents the age and sex distribution of a population, highlighting trends in birth rates, death rates, and overall population growth. By analyzing the shape of the pyramid, ecologists can infer whether a population is growing, stable, or declining, as well as predict future demographic changes and potential challenges related to resource allocation and social structures. Moreover, population pyramids can indicate the potential for future growth by showing the proportion of individuals in reproductive age versus those in non-reproductive age, thereby providing insights into reproductive trends and the sustainability of the population over time.
What are some reasons that smaller organisms typically have higher r values?
Smaller organisms often have higher r values due to their shorter lifespans, which allow them to reproduce more frequently within a given time period. Additionally, these organisms tend to produce larger numbers of offspring per reproductive event, increasing their overall reproductive output. Their ability to quickly exploit available resources and adapt to changing environments also contributes to their higher reproductive rates, enabling them to thrive in various ecological niches. Furthermore, smaller organisms often reach sexual maturity at a younger age, which accelerates the cycle of reproduction and enhances their population growth potential.
What happens when λ = 1? What about when it is < 1?
When ( \lambda = 1 ), it indicates that the population is stable, meaning that the number of individuals remains constant over time, with births equaling deaths. Conversely, when ( \lambda < 1 ), the population is declining, as the number of deaths surpasses the number of births, leading to a decrease in the overall population size. This decline can result from various factors, including limited resources, increased predation, or environmental changes that adversely affect survival and reproduction.
What are the assumptions of exponential growth?
The population grows in an ideal environment with unlimited resources.
Individuals in the population are assumed to be identical, with equal chances of survival and reproduction.
There are no immigration or emigration effects influencing population size.
The growth rate remains constant over time, regardless of population density.
What is an inflection point?
An inflection point is a point on a curve where the curvature changes sign, indicating a shift in the growth rate of the population; specifically, it marks the transition from accelerating growth to decelerating growth as resources become limited. An inflection point is a critical moment in population dynamics where the growth rate shifts, transitioning from exponential growth to a more stabilized growth phase, often due to resource limitations or environmental constraints.
Competition
Metapopulation
The metapopulation model views a population as a set of subpopulations occupying patches of a particular habitat:
Intervening habitat is referred to as the habitat matrix:
The matrix is viewed only as a barrier to movement of individuals between subpopulations
In metapopulations, sets of spatially isolated populations are linked by dispersal
Ex: kettle lake is a body of water that forms in a depression left behind by a melting block of ice
Metapopulations are characterized by repeated extinctions and colonization of small individual populations, but the metapopulation persists
Some populations serve as sources for colonization of sinks (populations that receive more immigrants than the number of emigrants they produce).
Habitat Fragmentation: Spatially isolated habitat 'fragments'
Ex: Mangrove forests, Rainforests, seagrass
Competition
Resources
Any substance or factor that is consumed by an organism and/or that supports increased population growth as its availability in the environment increases:
Resources include foods that are eaten but also include:
Open space for sessile (non-motile) organisms
Hiding places and other safe sites
Nonrenewable resources (ex: space over generational time scales)
Renewable resources (ex: nutrients, light, water)
Conditions are not resources
Competition: any use or defense of a resource by one individual that reduces the availability of the resource to other individuals
(-,-) both organisms are harmed as opposed to (+,-) one organism benefits and the other is harmed
Intraspecific competition:
Competition among members of the same species
Reduces resources in a density-dependent manner
dN/dt = rN [1-N/K]
Interspecific competition:
Competition among individuals of two or more species - reduces fitness of individuals of both species
Intensity depends on density of each species and degree of overlap of resource use
Modes of Competition
Exploitative competition:
Use of resources by one or more individuals, thereby reducing the availability of resources for other individuals
Interference competition:
Direct aggressive interaction between individuals
Example of Exploitative competition:
Trees being tall and skinny and only growing leaves at the top to get some sunlight (more than other trees near them)
Preemptive exploitative competition: occurs when individuals occupy space and prevent access to resource by other individuals
Sometimes both types of competition (exploitative and Interference)
Direct, aggressive encounters are classic examples of interference competition
Hyena and vultures fighting over food
Allelopathy: Chemical Interference
Chemical competition, most frequently reported among plants:
Typically mediated by toxic substances that causes direct harm to other individuals
The chemical inhibition of one plant (or other organism) by another, due to the release into environment of substances acting as germination or growth inhibitors
Classic Lab Studies of Competition
Gause 1934: Competitive exclusion principle
Two species using a limited resource in the same way can't exist indefinitely
If niche overlap is high, then competitive exclusion is hypothesized to result
If they compete for a long time, then the green species would go extinct over time
Concept of a niche
Best known definition of a niche is G. Evelyn Hutchinson 1957
Role that organism plays in the environment
Role can be determined by measuring all
of an organism's activities and requirements
Examples
By extension…niche defined as N- dimensional (having an arbitrary number of dimensions)
Encompasses all requirements of a species
Two types of niches
Fundamental: niche space determined by physical factors and resource requirements. Manifest in the absence of other organisms
Realized: niche space determined by combined physical and biological factors (comp. and predation).
Is an organism's realized niche always going to be smaller than its fundamental niche
Asymmetric Competition: niches do not overlap completely, then weaker competitors are forced to use a range of resources that does not overlap with the range of resources used by stronger competitor, reducing the realized niche of the weaker competitor
Evidence for Competition: Character Displacement
Occurs when the phenotypes of competing species evolve to become different over time
Through character displacement, natural selection favors individuals that do not compete
The Lotka-Volterra (L-V) Competition Equations
Goal:
Understand how mutual competition between species affects growth of both
Is the L-V interspecific competition model, as written here legitimate (complete?)
Bracket: unused portion of the carrying capacity
Unused portion of the carrying capacity is the portion of the frame left empty
K = 100 and N = 4
Unused portion of carrying capacity is: [ 1-(4/100)] = 0.96
dN/dt = rN(0.96)
Interspecific competition is incorporated into the logistic equation:
Consumptive Interactions
Over half the species on Earth gets energy by feeding on other organisms in a variety of type of interactions
All forms of predations - individuals of one species (predators) benefit by feeding on, and directly harming, individuals of another species (prey) (+,-)
Carnivory- both predator and prey are animals
Herbivory - predator is an animal, prey are plants or algae
Parasitism - predator (a parasite) lives symbiotically on or in the prey (its host) and consumes certain tissues; may not kill the host. Some parasites (pathogens) cause disease
Subdivision
Omnivores, mixotrophy
Many carnivores, such as bears, also eat berries, nuts, and leaves
Parasitoids: insects that lay eggs on or in another insect host, After hatching, larvae remain in the host, which they eat and usually kill
P = E/t
Carnivore and Herbivore Dietary Preferences
Optimal foraging and dietary preferences depend on:
Encounter rate - if low, predators should be generalists, not choosy
Handling time - if prey are easy to find but handling time is long, immobile but less nutritious plants, then predators (herbivores) should be specialists
Ecologists are interested in feeding rates and functional response
Feeding Rate Functional Responses
Type 1: Filter Feeders 1:1 ration(sponges)
Type 2: Consumes more as density increases but is limited by handling time: Humans
Type 3: t is bigger than E so they won't eat (mayflies)
Where are organisms found, how many are there, and why?
For parasites, external and internal feeding matters
Advantages and Disadvantages of External or Internal Feeding
Ectoparasitism:
Dispersal: Easier
Feeding: More difficult
Vulnerability to host's immune system: Very Low
Vulnerability to external abiotic factors: High
Vulnerability to natural Enemies: Moderate to High
Endoparasitism:
Dispersal: More reliant on host
Feeding: Easier High
Vulnerability to host's immune system: Low
Vulnerability to external abiotic factors: Low
Vulnerability to natural Enemies: Moderate
Parasites typically feed on only one or a few host species, but host species have multiple parasite species
Humans are an amalgamation of parasite BIOMES
Behavior-altering parasites
Parasites with two or more hosts, capable of causing changes in the behavior of one of their hosts to facilitate their transmission, sometimes directly affecting the hosts' decision-making and behavior control mechanisms
Parasitic Castrator
Host energy spent on reproduction include not just gonads and gametes but also secondary sexual characteristics, mate-seeking behavior, competition and care for offspring
Prolonged host life may also result from parasitic castration, benefiting parasite
Coevolution- adaption in a population of one species (predators, parasites) may change then natural selection pressure on a population of another species (prey, hosts), giving rise to common antagonistic coevolution
Costly and comes with tradeoffs
Define Resource and Explain Conditions: Resource: A resource is any substance or factor that organisms consume and that supports population growth when it is available. Unlike resources, conditions are environmental influences that affect growth and survival but are not consumed.
Explain Exploitation vs. Interference Competition:
Exploitation Competition: Utilization of shared resources by individuals, which decreases availability for others without direct interaction.
Interference Competition: Direct and aggressive interactions between individuals that restrict access to resources for competitors.
/
Temporal and Spatial Variation in Competition: Competition can change over time and space because of shifts in resource availability, population densities, and environmental factors. Seasonal changes and localized conditions create different competitive environments.
Define Asymmetrical Competition: Asymmetrical Competition occurs when one species negatively impacts another much more than vice versa, potentially leading to the exclusion of the less competitive species.
Fundamental vs. Realized Niche:
Fundamental Niche: The full potential range of environmental conditions and resources a species can utilize without competition.
Realized Niche: The actual conditions and resources utilized by a species, affected by competition and other interactions, often smaller than the fundamental niche.
Explain the Competitive Exclusion Principle: The Competitive Exclusion Principle states that two species competing for the same limited resources cannot coexist indefinitely. Coexistence can occur through niche differentiation and temporal resource use.
Define Niche Partitioning and Character Displacement: Niche Partitioning involves species reducing competition by utilizing different resources or using resources at different times, which can lead to character displacement—evolutionary changes that reduce competition.
Describe Predator Functional Response Types:
Type I Response: Linear increase in predation with prey density, common in filter feeders.
Type II Response: Increases in predation but levels off due to handling time, seen in many predators.
Type III Response: Predation low at low prey densities, increases at moderate densities, plateaus due to availability and handling time, seen in learning predators.
Why are Parasites Specialists?:Parasites are often specialists because they adapt to exploit specific host species efficiently, enhancing survival and reproductive success.
How do Behavior-Altering Parasites Facilitate Transmission?:Behavior-altering parasites influence their host's behavior to enhance their transfer to new hosts, sometimes increasing predation risk to ensure their transmission.
Effects Beyond Mortality from Predators and Parasites: Predators and parasites affect the fitness of prey and host populations by causing stress responses and influencing growth rates and reproduction, leading to shifts in population dynamics.
How can a Predator Create a Trophic Cascade?:A predator can initiate a trophic cascade, influencing herbivore populations and subsequently affecting vegetation, leading to ecological changes across trophic levels.
Components of Lotka-Volterra Predator-Prey Models: The models illustrate interactions between predator and prey populations, including prey growth influenced by reproduction and predation rates, leading to oscillating population dynamics.
Lotka-Volterra Competition Model Components: The model for two competing species is expressed as:
For species 1: dN1/dt = r1N1 (1 - (N1 + αN2)/K1)
For species 2: dN2/dt = r2N2 (1 - (N2 + βN1)/K2) Where α and β are competitive coefficients.
Predator Presence and Competition Outcomes: Predators can alter competitive outcomes by reducing the numbers of dominant competitors, allowing subordinate species to thrive and coexist.
Disturbances and Coexistence: Disturbances can reset competitive hierarchies, fostering coexistence between species with high asymmetrical competitive interactions by allowing weaker competitors to establish.
Barnacle Competition Dynamics: In Balanus vs. Chthamalus competition, the fundamental niche for Balanus is broader; however, Chthamalus often occupies higher intertidal zones where competition is less intense.
Carnivores as Generalists vs. Herbivores as Specialists: Yes, carnivores often act as generalists while herbivores are specialists, adapting to a limited range of plant species for optimal nutrient absorption.
Pros and Cons of Ecto- and Endoparasites:
Ectoparasites: Easier dispersal but vulnerable to environmental hazards.
Endoparasites: Nutrient access is easier, but more reliant on the host and exposed to immune responses.