Ø Chapter 53: Population Ecology
• Overview: Counting Sheep
• A small population of ______were introduced to Hirta Island in 1932
• They provide an ideal opportunity to study changes in population size on an isolated island with abundant food and no predators
• ______is the study of populations in relation to environment.
• A ______is a group of individuals of a single species living in the same general area.
• Three characteristics of a population are its ______
• Density and Dispersion
– ______ is the number of individuals per unit area or volume
• Ex: Number of maple trees in Cambria County
– ______ is the pattern of spacing among individuals within the boundaries of the population
• Density: A Dynamic Perspective
– In most cases, it is impractical or impossible to count ______ in a population
– ______can be used to estimate densities and total population sizes
– Population size can be estimated by either ______from small samples, an ______, or the ______
– Density is the result of an interplay between ______that ______ individuals to a population and those that ______ individuals
• ______ is the influx of new individuals from other areas
• ______ is the movement of individuals out of a population
• ______is the number of new individuals born into a population
• ______is the number of individuals that die in a population
• Patterns of Dispersal
– ______influence ______ of individuals in a population
– In a ______, individuals aggregate in patches. It is most common.
• A clumped dispersion may be influenced by ______
______
– A ______is one in which individuals are evenly distributed. Not as common as clumped.
• It may be influenced by social interactions such as ______
– In a ______, the position of each individual is independent of other individuals. Wind-blown seeds for example, are randomly dispersed. This is not real common in nature.
• It occurs in the ______
• Demographics
– ______ is the study of the vital statistics of a population and how they change over time
– ______ are of particular interest to demographers
• A ______is an age-specific summary of the survival pattern of a population
• It is best made by following the fate of a ______, a group of individuals of the same age
• The life table of Belding’s ground squirrels reveals many things about this population
• Survivorship Curves
– A ______is a graphic way of representing the data in a life table
– The survivorship curve for Belding’s ground squirrels shows a ______
– Survivorship curves can be classified into three general types:
• ______: low death rates during early and middle life, then an increase among older age groups
• ______: the death rate is constant over the organism’s life span
• ______: high death rates for the young, then a slower death rate for survivors
– Many species actually fall somewhere between these basic types of curves and show more complex patterns.
• Reproductive Rates
– For species with sexual reproduction, demographers often concentrate on females in a population
– A ______, or fertility schedule, is an age-specific summary of the reproductive rates in a population
– It describes reproductive patterns of a population
– Species vary greatly in their reproductive patterns. Why this happens is the focus of ______.
Ø Concept 53.2: Life history traits are products of natural selection
• An organism’s ______ comprises the traits that affect ______
______: It entails three basic variables:
– The age at which reproduction begins
– How often the organism reproduces
– How many offspring are produced during each reproductive cycle
• Life history traits are evolutionary outcomes reflected in the ______
______(i.e. except for humans, organisms ______ when to reproduce or how many offspring to have.)
• Evolution and Life History Diversity
– Life histories are very diverse.
• Some species that exhibit ______, or ______, reproduce once and die. Ex: Pacific Salmon
• Some species that exhibit ______, or ______, produce offspring repeatedly. Ex: Animals with seasonal mating seasons.
– ______ likely favor big-bang reproduction. Survival rate is low—even for adults. So the produce a lot of young once—in hopes that a few will survive to reproduce.
– ______ may favor repeated reproduction. Survival rate is good—for young and adults. The adults will survive to reproduce again. A few large young should also be able to survive to reproductive age.
• “Trade-offs” and Life Histories
– Organisms have ______, which may lead to ______
• ______limit the reproductive capabilities of all organisms.
• Selective pressures influence the trade-off between the ______.
Ø Concept 53.3: The exponential model describes population growth in an idealized, unlimited environment
• It is useful to study population growth in an ______
• Idealized situations help us understand the ______and the ______
• Per Capita Rate of Increase
– If immigration and emigration are ignored, a population’s growth rate (per capita increase) ______
– ______occurs when the birth rate equals the death rate
– Most ecologists use differential calculus to express population growth as growth rate at a particular instant in time:
• Exponential Growth
– ______is population increase under idealized conditions
– Under these conditions, the rate of reproduction is at its ______, called the ______
– ______ of exponential population growth:
– Exponential population growth results in a ______
– The J-shaped curve of exponential growth characterizes ______
______
Ø Concept 53.4: The logistic model describes how a population grows more slowly as it nears its carrying capacity
• Exponential growth ______ in any population
• A more realistic population model limits growth by incorporating carrying capacity
• ______is the maximum population size the environment can support
• The Logistic Growth Model
– In the ______model, the per capita rate of increase declines as carrying capacity is reached
– We construct the logistic model by starting with the exponential model and adding an expression that reduces per capita rate of increase as N approaches K
– The logistic model of population growth produces a ______
• The Logistic Model and Real Populations
– The growth of laboratory populations of paramecia fits an S-shaped curve
– These organisms are grown in a constant environment lacking predators and competitors
– Some populations ______ before settling down to a relatively stable density
– Some populations fluctuate greatly and make it difficult to define K
– Some populations show an ______, in which individuals have a more difficult time surviving or reproducing if the population size is too small
– The logistic model fits few real populations but is useful for estimating possible growth
• The Logistic Model and Life Histories
– Life history traits favored by natural selection may vary with ______
______
• ______, or density-dependent selection, selects for life history traits that are sensitive to population density
• ______, or density-independent selection, selects for life history traits that maximize reproduction
Ø Concept 53.5: Many factors that regulate population growth are density dependent
• There are two general questions about regulation of population growth:
– ______ stop a population from growing indefinitely?
– Why do some populations show radical ______ in size over time, while others ______?
• Population Change and Population Density
– In ______populations, birth rate and death rate ______ with population density
– In ______ populations, birth rates fall and death rates rise with population density
– The following diagrams show how a population may stop increasing and reach equilibrium as a result of various combinations of density-dependent and density-independent regulation.
• Density-Dependent Population Regulation
– Density-dependent birth and death rates are an example of ______that ______
– They are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors
• Territoriality
– In many vertebrates and some invertebrates, ______
______
• Disease
– Population density can influence the health and survival of organisms
– In dense populations, ______
• Predation
– As a prey population builds up, predators may ______ on that species
• Toxic Wastes
– ______ can contribute to density-dependent regulation of population size
• Intrinsic Factors
– For some populations, ______factors appear to regulate population size
• Population Dynamics
– The study of ______ focuses on the interactions between ______ that cause variation in population size
– Two examples:
• Long-term population studies have challenged the hypothesis that populations of large mammals are relatively stable over time. The sheep mentioned at the beginning of the chapter are an example of this. ______ seems to greatly affect their population size over time
• In another example: Changes in predation pressure can drive population fluctuations. The following graph shows the fluctuations in moose and wolf populations on an isolated island.
• The moose population crashed twice: once when the wolf population was at its peak and once following a terribly harsh winter.
• Population Cycles: Scientific Inquiry
– Some populations undergo regular ______
– ______ populations follow the 10 year boom-and-bust cycle of ______populations
– Three hypotheses have been proposed to explain the hare’s 10-year interval
– Hypothesis #1: The hare’s population cycle follows a cycle of winter food supply
• If this hypothesis is correct, then the cycles ______
• Additional food was provided experimentally to a hare population, and the whole population increased in size ______
– Hypothesis #2: The hare’s population cycle is ______
• In a study conducted by field ecologists, 90% of the hares were killed by predators
• No hares appeared to have died of starvation
• These data support this second hypothesis
– Hypothesis #3: The hare’s population cycle is ______
• Sunspot activity affects light quality, which in turn affects the ______
• There is good correlation between sunspot activity and hare population size
• The results of all these experiments suggest that ______predation ______ sunspot activity regulate hare numbers and that food availability plays a less important role
• Immigration, Emigration, and Metapopulations
– ______ are groups of populations linked by immigration and emigration
– High levels of immigration combined with higher survival can result in greater stability in populations
Ø Concept 53.6: The human population is no longer growing exponentially but is still increasing rapidly
• No population can grow indefinitely, and humans are no exception
– Human population increased rather slowly until 1650, at which time there were about 500 million people on Earth.
– We doubled to 1 billion within the next two centuries
– Doubled again to 2 billion between 1850 and 1930.
– Doubled again to 4 billion by 1975
– We are now more than 6.6 billion (increasing by about 75 million each year; or 200,000 each day)
– It is predicted that a population of 7.8 – 10.8 billion people will inhabit Earth by 2050.
• Regional Patterns of Population Change
– To maintain population stability, a regional human population can exist in one of two configurations:
• Zero population growth = High birth rate – High death rate
• Zero population growth = Low birth rate – Low death rate
• The demographic transition is the move from the first state toward the second state
• The ______is associated with an increase in the quality of health care and improved access to education, especially for women
– Most of the current global population growth is concentrated in developing countries
• Age Structure
– One important demographic factor in present and future growth trends is a country’s ______
– Age structure is the ______
– Age structure diagrams can predict a ______
– They can ______ and help us plan for the future
• Infant Mortality and Life Expectancy
– Infant mortality and life expectancy at birth vary greatly among ______countries but do not capture the wide range of the human condition
• Global Carrying Capacity
– How many humans can the ______?
– The carrying capacity of Earth for humans is ______
– The ______
• Limits on Human Population Size
– The ______concept summarizes the ______to sustain the people of a nation
– It is ______ we are to the carrying capacity of Earth
– Countries vary greatly in ______and available ecological capacity
– One way to estimate the ______ of the human population is to add up all the ecologically productive land on the planet and divide by the population.
– This calculates to about ______.
– Typically, we reserve some land for parks and conservation so the actual number used is ______.
– One who consumes more resources than can be produced on 1.7 ha is using ______.
– The average person in the U.S. has an ecological footprint of ______.
– Our carrying capacity could potentially be limited by ______
______
– ______, we ______whether zero population growth will be attained through social changes based on human choices or through increased mortality due to resource limitation, plagues, war and environmental degradation.
You should now be able to:
1. Define and distinguish between the following sets of terms: density and dispersion; clumped dispersion, uniform dispersion, and random dispersion; life table and reproductive table; Type I, Type II, and Type III survivorship curves; semelparity and iteroparity; r-selected populations and K-selected populations