Populations 43

Chapter 43 Populations Key Concepts Populations Are Patchy in Space and Dynamic over Time Births Increase and Deaths Decrease Population Size Life Histories Determine Population Growth Rates Populations Grow Multiplicatively, but Not for Long Extinction and Recolonization Affect Population Dynamics Ecology Provides Tools for Managing Populations

Concept 43.1 Populations Are Patchy in Space and Dynamic over Time Population—all the individuals of a species that interact with one another within a given area at a particular time. Population density—number of individuals per unit of area or volume Population size—total number of individuals in a population Counting all individuals is usually not feasible; ecologists often measure density, then multiply by the area occupied by the population to get population size.

Concept 43.1 Populations Are Patchy in Space and Dynamic over Time Abundance varies on several spatial scales. Geographic range—region in which a species is found Within the range, species may be restricted to specific environments or habitats. Habitat patches are “islands” of suitable habitat separated by areas of unsuitable habitat.

Concept 43.1 Populations Are Patchy in Space and Dynamic over Time Population densities are dynamic—they change over time. Density of one species population may be related to density of other species populations.

Math Practice go to: Population worksheet & print this out to follow alongworksheet

Concept 43.2 Births Increase and Deaths Decrease Population Size Change in population size depends on the number of births and deaths over a given time. “Birth–death” or BD model of population change: Example” Population 200 = 1,000 births-800 deaths t-time, t+1 time, =N=population, B=birth, d=death

Concept 43.2 Births Increase and Deaths Decrease Population Size Population growth rate (how fast it is changing): Δ= change, all other letters same as last slide Example (easier than below) BR-DR/10 Why 10? expressed as a percent Example /10=20% For the bottom equation example use the sheet from the web site to guide you. This is rate change over time.

Concept 43.2 Births Increase and Deaths Decrease Population Size Per capita birth rate (b)—number of offspring an average individual produces Per capita death rate (d)—average individual’s chance of dying Per capita growth rate (r) = (b – d) = average individual’s contribution to total population growth rate If b > d, then r > 0, and the population grows. If b < d, then r < 0, and the population shrinks. If b = d, then r = 0, and population size does not change.

Concept 43.5 Extinction and Recolonization Affect Population Dynamics The BIDE model of popultion growth adds the number of immigrants (I) and emigrants (E) to the BD growth model.

Which of the following factors can explain a decline in the size of a population through time? a. Per capita birth rates b have decreased b. Per capita death rates d have decreased c. Per capita death rates d have increased d. Both a and c e. None of the above Concept 43.2 Births Increase and Deaths Decrease Population Size

Concept 43.4 Populations Grow Multiplicatively, but Not for Long Population growth is multiplicative—(exponential) an ever-larger number of individuals is added in each successive time period. Think of compounding interest on savings. In additive growth, a constant number (rather than a constant multiple) is added in each time period.

Concept 43.4 Populations Grow Multiplicatively, but Not for Long r decreases as the population becomes more crowded; r is density dependent. Density dependent factors-birth rate, mates, competition As the population grows and becomes more crowded, birth rates tend to decrease and death rates tend to increase. Density Independent Factors- disease, weather, hunting When r = 0, the population size stops changing—it reaches an equilibrium size called carrying capacity, or K.

Concept 43.4 Populations Grow Multiplicatively, but Not for Long Multiplicative growth has a constant doubling time. The time it takes a population to double in size can be calculated if r is known. To calculate =70/r, AKA, Rule of 70. Example how many years will it take to double a population if rate of increase is 20%? 3.5 years In this graph we see Rate will slow over time When the population reaches K=carrying capacity Exponential growth Logistical growth curve

Concept 43.3 Life Histories Determine Population Growth Rates A life table shows ages at which individuals make life cycle transitions and how many individuals do so successfully. Life tables have two types of information: survivorship—fraction of individuals that survive from birth to different life stages or ages fertility—average number of offspring each individual produces at those life stages or ages

Figure 43.4 Resource Acquisition Increases with Resource Availability (Part 3)

Concept 43.3 Life Histories Determine Population Growth Rates Principle of allocation—once an organism has acquired a unit of some resource, it can be used for only one function at a time: maintenance, foraging, growth, defense, or reproduction. In stressful conditions, more resources go to maintaining homeostasis. Once an organism has more resources than it needs for maintenance, it can allocate the excess to other functions.

Figure 43.5 The Principle of Allocation

Concept 43.3 Life Histories Determine Population Growth Rates What’s the take away about resource acquisition? The more we take, the more resources are available to us as humans, the less available they are to other organisms. This leads to stress on an community and can lead to death, extinction, loss of diversity.

Concept 43.4 Populations Grow Multiplicatively, but Not for Long Charles Darwin was aware of the power of multiplicative growth: “As more individuals are produced than can possibly survive, there must in every case be a struggle for existence.” This ecological struggle for existence, fueled by multiplicative growth, drives natural selection and adaptation.

Figure 43.7 Environmental Conditions Affect Per Capita Growth Rates and Species Distributions (Part 1) Which insect pop. Performed better in higher temperatures?

Figure 43.8 Per Capita Growth Rate Decreases with Population Density (Part 1)

Figure 43.8 Per Capita Growth Rate Decreases with Population Density (Part 2)

Concept 43.6 Ecology Provides Tools for Managing Populations Understanding life history strategies can be useful in managing other species. Fisheries: Black rockfish grow throughout their life. The number of eggs a female produces is proportional to her size. Older, larger females also produce eggs with oil droplets that give the larvae a head start on growth. Fishermen prefer to catch big fish. Intense fishing reduced the average age of female rockfish from 9.5 to 6.5 years. These younger females were smaller, produced fewer eggs, and larvae didn’t survive as well. Management may require no-fishing zones where some females can mature and reproduce.

Concept 43.6 Ecology Provides Tools for Managing Populations Conservation plans begin with inventories of habitat and potential risks to the habitat. Largest patches can potentially have the largest populations and are given priorty. Quality (carrying capacity) of the patches is evaluated; ways to restore or maintain quality are developed. Ability of the organism to disperse between patches is evaluated.

Concept 43.6 Ecology Provides Tools for Managing Populations For some species, a continuous corridor of habitat is needed to connect subpopulations and allow dispersal. Dispersal corridors can be created by maintaining vegetation along roadsides, fence lines, or streams, or building bridges or underpasses that allow individuals to avoid roads or other barriers.