1. Chapter 8 Environmental Science
Understanding Populations

2. Bellringer

3. Objectives Describe the three main properties of a population.
Describe exponential population growth.
Describe how the reproductive behavior of individuals can affect the growth rate of their population.
Explain how population sizes in nature are regulated.

4. How Populations Change in Size
Charles Darwin calculated that a single pair of elephants could theoretically produce 19 million descendants within 750 years, making the point that the actual number of elephants is limited by their environment.

5. A. What is a Population?
Population – all the members of a species living in the same place at the same time
-a population is a reproductive group because organisms usually breed with members of their own population
-population also refers to the size – or number of individuals it contains

6. B. Properties of Populations
Populations can be described in terms of size, density, or dispersion
Density – the number of individuals per unit area or volume
Dispersion – relative distribution or arrangement of its individuals within a given amount of space
-dispersion may be even, clumped, or random

7. C. How Does a Population Grow?
A population grows with births and shrinks with deaths.
Population change over time is represented by:

8. Growth rate Growth rate – change in a population’s size over time
Over time, the growth rates change in a population because birth and death rates increase or decrease

9. Growth rates can be positive, negative, or zero
for a zero population growth the average number of births must equal the average number of deaths
-a population would remain the same size if each pair of adults produced exactly two offspring and each of those offspring survived to reproduce
-if the adults in a population are not replaced by new births, the growth rate will be negative and the population will shrink

10. D. How Fast Can a Population Grow?
Populations usually stay about the same size from year to year because various factors kill many individuals before they can reproduce

11. Biotic potential
Biotic potential – the fastest rate at which its populations can grow
-this number is limited by the maximum number of offspring that each member of the population can produce – reproductive potential

12. Reproductive Potential
some species have much higher reproductive potentials than others
-750 years for a pair of elephants to produce 19 million descendants
It takes a few days or weeks for a single bacterium to produce 19 million descendants
Reproductive potential increases when
-individuals produce more offspring at a time
-reproduce more often
-reproduce earlier in life – this has the greatest effect on reproductive potential

13. Early reproduction shortens the generation time – the average time it takes for member of the population to reach the age when it reproduces
Small organisms like bacteria and insects have short generation times
-they can reproduce when they are a few hours or days old
-their populations can grow quickly
Large organisms like elephants and humans become sexually mature after a number of years
Human generation time is about 20 years so humans have a much lower reproductive potential

14. Exponential Growth
In exponential growth, a large number of individuals is added to the population in each succeeding time period.

15. Exponential growth
Exponential growth – when a population grows faster and faster
-graph represents a J-curve
-occurs in nature only when populations have plenty of food and space and have no competition or predators

16. E. What Limits Population Growth?
Because natural conditions are neither ideal nor constant, populations cannot grow forever and rarely grow at their reproductive potential
-eventually resources are used up or the environment changes, and deaths increase or births decrease
-under the forces of nature only some members of a given population will survive and reproduce, thus the properties of a population may change over time

17. Carrying capacity
Carrying capacity – the maximum population that the ecosystem can support indefinitely
-a population may increase beyond this number, but it cannot stay that way for long
-because ecosystems change it is difficult to predict or calculate exactly
-can be estimated by looking at average population sizes or by observing a population crash after a certain size has been exceeded
example: Rabbits in Australia are the most serious mammalian pests, an invasive species whose destruction of habitats are responsible for the extinction or major decline of many native animals

18. Resource limits
a species reaches its carrying capacity when it consumes a particular natural resource at the same rate at which the ecosystem produces the resource called the limiting resource
plant growth is limited by supplies of water, sunlight, and mineral nutrients
-supply of the most severely limited resources determines the carrying capacity of an environment for a particular species at a particular time

19. Carrying Capacity

20. Competition
-members of a population use the same resources in the same ways so they will eventually compete with one another as the population approaches its carrying capacity
-instead of competing for a resource such as food, individuals can compete for territory
-territory – an area defended by one or more individuals against other individuals
area valuable for the shelter, food, or breeding sites it contains
competition is part of the pressure of natural selection

21. F. Two Types of Population Regulation
Population size can be limited in ways that may or may not depend on the density of the population
causes of death in a population can be density-dependent or density-independent

22. Density-dependent
Density-dependent – when deaths occur more quickly in a crowded population than in a sparse population
-happens when individuals in a population are densely packed together such as when a population is growing rapidly
-competition for resources, mates, disease

23. Density-independent
Density-independent – when a certain proportion of a population dies regardless of the population’s size
-this type of regulation affects all populations in a general or uniform way
-severe weather, natural disasters, etc.

24. Quick LAB

25. Math Practice

26. Bellringer

27. Objectives Explain the difference between niche and habitat.
Give examples of parts of a niche.
Describe the five major types of interactions between species.
Explain the difference between parasitism and predation.
Explain how symbiotic relationships may evolve.

28. II. How Species Interact with Each Other
A. An Organism’s Niche
Niche – the unique role of a species within an ecosystem
-includes the species’ physical home, environmental factors necessary for the species’ survival, all of the
other species’ interactions with other organisms

29. Niche
-a niche is different from a habitat – habitat is location, but niche is an organism’s pattern of use of its habitat
-the functional role, or job of a particular species in an ecosystem

30. B. Ways in Which Species Interact
The five major types of species interaction
competition, predation, parasitism, mutualism, and commensalism
Based on whether each species causes benefit or harm to the other species
Many interactions cannot be categorized or well studied

31. Species Interactions

32. C. Competition
Competition – a relationship in which different individuals or populations attempt to use the same limited resource
-each individual has less access to the resource and so is harmed by the competition
-competition can occur both within and between species

33. 2 Types of Competition
-intraspecific competition – occurs among individuals of the same species
Ex: Deer against Deer
-interspecific competition – occurs between different species
Ex: Deer against Rabbit
-members of the same species must compete with each other because they require the same resources because they occupy the same niche

34. Overlap
Resource use
-overlap – when members of different species compete for the same resources their niches overlap
-each species uses some of the same resources in a habitat
Number of individuals
Species 1
Species 2
Region of
niche overlap

35. Indirect competition
-species can compete even if they never come into direct contact with each other
-if one insect species feeds on a certain plant during the day and another species on the same plant at night
-two plants that flower at the same time compete for pollinators
-humans and the insects that eat our crops – both compete for the same crops

36. Adaptations to competition
-when two species with similar niches are placed together in the same ecosystem
-one species will probably be more successful than another
-the better adapted would be able to use more of the niche
-during the course of evolution adaptations that decrease competition would be advantageous for those species whose niche’s overlap

37. Adaptations to Competition

38. Law of competitive exclusion
Law of competitive exclusion – no two species can occupy the same ecological niche for very long
Competition can be reduced between species is by dividing up the niche in time or space
-niche restriction – when each species uses less of the niche than they are capable of using

39. Sharing observed in closely related species that use the same resources within a habitat-resource partitioning
Black-throated Green Warbler
Cape May Warbler
Bay-breasted Warbler
Yellow-rumped Warbler

40. D. Predation Predation – an organism that feeds on another organism
predator – the organism that eats, prey – the organism that gets eaten
Food webs can make predation a complicated interaction, the prey of one species can be the predator of another
Most organisms have evolved some mechanisms to avoid or defend against predators

41. CASE STUDY
camouflage, toxic chemicals, warning coloration, mimicry – 2 types, protective covering
Predator/prey populations tend to fluctuate together

42. Predators
Some predators eat only specific types of prey. In this kind of close relationship, the sizes of each population tend to increase and decrease in linked patterns, as shown below.

43. E. Parasitism
Parasite – an organism that lives in or on another organism and feeds on it
Host – the organism the parasite takes its nourishment from
Parasitism – the relationship between the parasite and the host

44. Bed Bugs

45. Parasites
ticks, fleas, tapeworms, heartworms, bloodsucking leeches, and mistletoe
Somewhat like predators except parasites spends some or all of its life in or on its host, and do not usually kill their host
A parasite can have an evolutionary advantage if it allows its host to live longer
Usually the host is weakened or exposed to disease by the parasite

46. Mistletoe

47. Mistletoe
Mistletoes have specialized roots with the ability to penetrate a host plant and absorb nutrients. Most mistletoe species are either full parasites like dwarf mistletoes (Arceuthobium spp.) or partial parasites, called hemiparasites, like the mistletoes (Viscum and Phoradendron spp.) used for holiday decoration.
Hemiparasites get a portion of their nourishment from their host, but they also contain chlorophyll, making them green and giving them the ability to conduct photosynthesis and make some sugars for themselves. The berries of most mistletoe species are white, but they can also be yellowish or even pink to red. Most parts of a mistletoe plant are toxic and should not be eaten.

48. F. Mutualism
Mutualism - a close relationship between two species in which each species provides a benefit to the other
-certain species of bacteria in the intestines of humans
-they help break down food, provide with vitamins and we provide it with a warm, food-rich habitat
Ant & acacia trees in Central America

49. G. Commensalism
Commensalism –a relationship in which one species benefits and the other is neither harmed nor helped
sharks and a fish called remoras – attach to sharks and feed on scraps of food left over from their meals
when birds nest in trees

50. H. Symbiosis and Coevolution
Symbiosis – a relationship in which two organisms live in close association with each other
parasitism, mutualism, commensalism are examples

51. Symbiosis
mostly used to describe situations in which at least one species benefits
Over time, species in a close relationship may coevolve – meaning they develop adaptations that reduce the harm or improve the benefit of the relationship
-coevolution is seen in the relationships of flowering plants and their pollinators

52. Graphic Organizer