51 Population Ecology Flashcards
Population ecology
the study of how and why the number of individuals in a population changes over time and space
Range
geographic distribution of a species
What factors determine range?
abiotic factors (e.g. temperature, rainfall, geographical structures, large-scale historical processes like continental drift) and biotic factors (e.g. past and current presence of other species that provide habitat, food, or competition)
Population density
the number of individuals of a population per unit area
What are the types of arrangement of individual organisms within populations?
Random, clumped, uniform
Random arrangement
the position of each individual is independent of the others e.g. seeds dispersed by the wind
Clumped arrangement
the quality of the habitat is patchy or the organisms associate in social groups e.g. schools of fish
Uniform arrangement
negative interactions occur among individuals e.g. competition for space, water, or other resources
Metapopulation “beyond population”
a population made up of many small, physically isolated populations connected by migration; individuals from a species form many independent populations
How can the population size, density, or distribution pattern of individuals be determined?
sampling methods
Sampling method for sedentary or sessile (immobile) organisms
(1) Counting individuals that occur along transects or inside quadrats set up at random locations in the habitat (2) Counts are extrapolated to the entire habitat area to estimate population size (3) Counts are compared to later sampling efforts to document trends over time
Transects and quadrats
lines of known position and length; rectangular plots
Sampling method for mobile organisms
individuals can be captured and tagged to estimate the total population size by using mark-recapture
Mark-recapture study
(1) researchers catch individuals and mark them with leg bands, ear tags, or some other permanent/temporary identification (2) marked individuals are released and allowed to mix with those unmarked for a period of time (3) marked individuals are recaptured and recorded
What assumptions are made when estimating total population (N) in mark-recapture?
(1) Percentage of marked individuals (M) in the total population (N) = average percentage of marked individuals (m) found in each recapture sample (n); (2) Individuals are not moving in and out of study area; (3) Individuals mix between recaptures; (4) No bias regarding which individuals are recaptured; (5) Individuals do not learn to avoid or seek out traps after being caught; (6) Individuals do not change their behavior
What 4 processes do the number of individuals in a population depend on?
birth, death, immigration, and emigration
Immigration
the migration of individuals INTO a particular population from other populations
Emigration
the migration of individuals AWAY from one population to other populations
Demography
the study of factors that determine the size and structure of population through time
Age structure
the proportion of individuals in a population that are of each possible age
Generation
the average time between a mother’s first offspring and her daughter’s first offspring
Life table
a data set that summarizes the probability that an individual in a certain population will survive and reproduce in any given year over the course of its lifetime
2 general approaches to collecting data for life tables
tracking individuals from short-lived species over time AND taking a snapshot of the age structure of a population from longer-lived species at one particular time
Age class
all the individuals of a specific age in a population
Cohort
a group of individuals that are the same age and can be followed through time
Survivorship
on average, the proportion of offspring that survive to a particular age (the opposite of mortality); resistance to disease and predators
Survivorship curve
a graph depicting the percentage of a population that survives to different ages, with the number of survivors in the y-axis and age on the x-axis
Type 1 survivorship curve
survivorship throughout life is high and then drops dramatically in old age, indicating that most individuals approach the species’ maximum life span
Type 2 survivorship curve
individuals have about the same probability of dying in each year of life
Type 3 survivorship curve
extremely high death rates (low survivorship) for larvae or seedlings but high survival rates later in life
Fecundity
the average number of female offspring produced by a single female in the course of her lifetime
Age-specific fecundity
the average number of female offspring produced by a female in a certain age class
Net reproductive rate (R₀)
the growth rate of a population per generation; equivalent to the average number of female offspring that each female produces over her lifetime; the sum of the products of survivorship and fecundity
When is the population increasing or decreasing?
increasing when R₀ > 1 and decreasing when R₀ < 1
Fitness trade-off
inescapable compromise between 2 traits that cannot be optimized simultaneously e.g. survivorship and fecundity
Life history
sequence of events in an individual’s life from birth to reproduction to death, including how an individual allocates resources to growth, reproduction, and activities or structures related to survival
Per capita “for each head” rate of increase (r)
or instantaneous rate of increase; the difference between the birth rate per individual and the death rate per individual
Exponential population growth
the accelerating increase in the size of a population that occurs when the per capita growth rate (r) is constant and density independent; cannot continue indefinitely because resources are not infinite
Intrinsic rate of increase (rmax)
the rate of increase of a population when conditions are ideal (birth rates per individual are as high as possible and death rates per individual are as low as possible)
How is exponential growth density independent?
it’s a type of population growth that does not vary with population density (or size)
What two types of circumstances is exponential growth common in?
(1) Colonization of a new habitat with plentiful resources (2) Recovery after a disaster
Carrying capacity (K)
the maximum population size of a certain species that a given habitat can support over a sustained period of time; varies among species and populations and changes over time
Logistic population growth
the density-dependent decrease in growth rate as population size approaches the carrying capacity
What happens as population size approaches carrying capacity?
(1) Growth is exponential and r is constant (2) N increases to the point where competition for resources or other density-dependent factors occur and growth declines (3) Growth rate is 0 when population is at carrying capacity
What factors regulate population size?
Density-independent factors and density-dependent factors
Density-independent factors
alter birth rates and death rates irrespective of the number of individuals in the population, and usually involve changes in the abiotic environment (e.g. variation in weather patterns, catastrophic events)
Density-dependent factors
change in intensity as a function of population size, and are usually biotic e.g. competition for resources (intraspecific), disease and parasitism (interspecific), predation (inter), toxic wastes, social behavior (intra)
Population
group of individuals of the same species, in the same place
