1. The characteristics of populations are shaped by the interactions between individuals and their environment

Transcription

1 1. The characteristics of populations are shaped by the interactions between individuals and their environment Populations have size and geographical boundaries. The density of a population is measured as the number of individuals per unit area. The dispersion of a population is the pattern of spacing among individuals within the geographic boundaries.

2 Measuring density of populations is a difficult task. We can count individuals; we can estimate population numbers. Fig. 52.1

3 Unfortunately, it is usually impractical to attempt to count all the individuals in a population. One sampling technique that researchers use is known as the mark-recapture method. Individuals are trapped in an area and captured, marked with a tag, recorded, and then released. After a period of time has elapsed, traps are set again, and individuals are captured and identified. This information allows estimates of population changes to be made.

4 The Lincoln Index is one such way Population size = n 1 x n n 3 n1 = # initially caught, marked and released n2 = # caught in second sample n3 = # of marked individuals in second sample

5 1. Here s the EOC stuff. The exponential model of population describes an idealized population in an unlimited environment We define a change in population size based on the following verbal equation. Change in population = Births during - Deaths during size during time interval time interval time interval In addition to this, add immigration and subtract emigration.

6 Using mathematical notation we can express this relationship as follows: If N represents population size, and t represents time, then N is the change is population size and t represents the change in time, then: N/ t = B-D + immigration emigration. Where B is the number of births and D is the number of deaths MIGRATION is the other way that population size might change. Births, deaths, migration.

7 If B = D then there is zero population growth (ZPG). Under ideal conditions, a population grows slowly at first (the lag phase), because there are few reproducing individuals, then very rapidly. Exponential population growth is said to be happening, like with the tribbles.

8 Fig. 52.9

9 2. The logistic model of population growth incorporates the concept of limiting factors that determine carrying capacity Typically, unlimited resources are rare. Population growth is therefore regulated by carrying capacity (K), which is the maximum stable population size a particular environment can support.

10 This is logistic growth - lag, exponential growth, then biotic and abiotic limiting factors (food, space, water, predators, etc.) slows growth and keeps the population around the carrying capacity. Fig

11 How well does the logistic model fit the growth of real populations? The growth of laboratory populations of some animals fits the S-shaped curves fairly well. Fig a, b

12 Some of the assumptions built into the logistic model do not apply to all populations. It is a model which provides a basis from which we can compare real populations. Fig c

13 Introduction What environmental factors stop a population from growing? Name some biotic factors. Some abiotic ones? Remember those for an aquatic ecosystem? The first step to answering these questions is to examine the effects of increased population density.

14 1. Negative feedback prevents unlimited population growth. Like temp. control! Many factors can cause negative feedback. Resource limitation in crowded populations can stop population growth by reducing reproduction. Fig.52.14

15 Intraspecific competition for food can also cause density-dependent behavior of populations. Territoriality, defense of a space, may set a limit on density. Predation may also be a factor because it can cause mortality of prey species. These are biotic factors. Fig

16 How about the effect of these EOC things? Seasonal variation Climate change Catastrophic events Human impact Invasive, non-native, introduced species

17 1. The human population has been growing almost exponentially for three centuries but cannot do so indefinitely The human population increased relatively slowly until about 1650 when the Plague took an untold number of lives. Ever since, human population numbers have doubled twice How might this population increase stop?

18 Fig

19 Age structure. Age structure is the relative number of individuals of each age. Age structure diagrams can reveal a population s growth trends, and can point to future social conditions.

20 Fig

21 2. Estimating Earth s carrying capacity for humans is a complex problem Predictions of the human population vary from 7.3 to 10.7 billion people by the year Will the earth be overpopulated by this time? How about some practice questions?

22 Thick, low clouds, like sea ice, reflect more sunlight than the open ocean. How would an increase in the number of low clouds over the Arctic Ocean most likely affect the polar bears? A. The amount of sea ice would increase, giving the bears more area in which to hunt B. The amount of sea ice would increase, making it harder for the bears to find mates C. The amount of sea ice would decrease, giving the bears less area in which to hunt D. The amount of sea ice would decrease, making it easier for the bears to find and capture seals

23 Biodiversity refers to the number of different kinds of organisms living in an ecosystem. Which of the following is least likely to reduce the biodiversity in an ecosystem? A. Farmers in an area clear several hundred hectares of forest to grow crops B. Heavy rains cause major flooding in an area, destroying many trees and homes C. When there is a shortage of their usual food, birds switch to a different food source D. People release unwanted pet snakes from a foreign country into the wild

24 A non-native species is introduced into an ecosystem. How might this introduction harm native species in the ecosystem? A. It might result in an increase in predation B. B. It might result in an increase in available prey C. It might result in a decrease in predation D. It might result in a decrease in pathogens

25 Different ecosystems can support different numbers of organisms. Which of the following is the number of individuals of a species that a particular ecosystem can support? A. Population B. Community C. Biotic potential D. Carrying capacity

26 The growth of populations is limited by factors in the ecosystem. Which of the following is an abiotic limiting factor? A. Parasites B. Pathogens C. Predators D. Soil nutrients

27 If the climate in southern Florida changed so that it was hot and dry year-round, with very little rain, which of the following would most likely occur? A. Plant diversity in the area would increase B. Animals in the area would find ways to adapt C. Plants usually found in deserts would begin to grow in the area D. Animals in the area would begin seasonal migrations

28 Corals live near the surface of the ocean water in some warm regions of the world. The corals provide a home for algae. The algae, in turn, produce food that is used by the corals. Which is a biotic factor in this ecosystem? A. Temperature of the water B. Salt content of the water C. The size of the algae population D. The amount of sunlight that reaches the coral