Environmental Science Chapter 4

Section 1 Objectives: 1. Describe the different levels of organization studied by ecologists 2. Explain the difference between biotic and abiotic factors. 3. Discuss how an organism’s habitat relates to its survial.

Section 1 The Central Case How do changes in population size relate to environmental conditions?

Section 1 Scientists study life at many levels, from individual organisms to the entire biosphere. Lets begin by taking a look at those different levels……………

Section 1 Ecology (figure 1) – Ecologist

Section 1 Levels of ecological organization 1. Individuals What ecologists study: 2. Populations

Section 1 Species 3. Communities What ecologists study:

Section 1 4. Ecosystems – What ecologists study 5. The Biosphere

Section 1 Ecosystems include both biotic and abiotic factors.

Section 1 The specific environment in which an organism lives is its ____________________. It consists of both ________________ and ____________________ factors. Anything an organism needs, including nutrition, shelter, breeding sites, and mates is a _________________________.

Section 2 Objectives: 1. Explain the usefulness of tracking population size. 2. Describe population density. 3. Describe the 3 ways populations can be distributed. 4. Explain what age structure diagrams tell you about a population.

Section 2 The overall health of a population can often be monitored by tracking how its size changes, population density changes, and distribution changes. The number of individual organisms present in a given population at a given time is called the _______________________.

Section 2 If a population size increases or remains the same it is a sign of a _______________________________________. If a population size decreases it can lead to __________________________________. The Passenger Pigeon

Section 2 Determining population size Do you think Alexander Wilson actually counted 2 billion passenger pigeons??? NO!!!! He took a SAMPLE

Section 2 They take a reasonable area, count the number of individuals, and estimate the number of individuals of a much larger area. Scientists also look for EVIDENCE that the organisms exist. Animal droppings or tracks

Section 2 The number of individuals within a population per unit area describes the ____________________ ___________________. High population densities Pros: Cons:

Section 2 The number of individuals within a population per unit area describes the ____________________ ___________________. High population densities Pros: Cons:

Section 2 Low population densities Pros: Cons:

Section 2 How the organisms are arranged within an area is called __________________ ___________________________. Populations can be arranged ________________, ___________________, or in ____________________.

Section 2 Random distribution: Uniform distribution: Clumped distribution:

Section 2 Age structure and sex ratios This describes the relative numbers of organisms of each age within a population: ___________ ________________. ______ ____________________ ____________ are visual tools to show the age structure of populations.

Section 2 Pre-reproductive organisms: Post-reproductive organisms: The proportion of males to females in a population describes _____________ __________.

Section 3 Objectives: 1. Describe the factors that influence a population’s growth rate. 2. Explain exponential growth and logistic growth. Explain how limiting factors and biotic potential affect population growth.

Section 3 A population’s growth rate is determined by births, deaths, immigration, and emigration. The rate at which individuals are born is called _________________________. The rate at which individuals die is called ___________________________.

Section 3 To show how the likelihood of death varies with age, population ecologists use graphs called _______________ ___________. There are 3 types of survivorship curves: I: II: III:

Section 3 Population size can also be affected by people moving in or out of a population. ____________ is the arrival of individuals from outside a given area. _____________ is the departure of individuals from a given area. _________________ is the seasonal movement into and out of an area.

Section 3 Calculating Population Growth (individuals added)-(individuals subtracted) = population growth Or (birthrate + immigration rate)-(death rate + emigration rate) = population growth Example:

Section 3 How populations grow Growth rates change depending on resources available to the organisms in the population 2 ways for populations to grow: 1. 2. 1. _______________________ occurs when a population increases by a fixed percentage each year Produces a J-shaped curve on a graph

Section 3 1. _______________________ occurs when a population increases by a fixed percentage each year Produces a J-shaped curve on a graph Exponential growth occurs when: 1. 2. Examples: 1. Mold growing on bread 2. bacteria growing on dead organisms

Section 3 2. ___________________ describes how a population’s initial exponential increase is slowed and finally stopped by limiting factors. Produces an S-curve on a graph ____________ are characteristics of the environment that limit population. _____________ is the largest population size a given environment can sustainably support.

Section 3 Limiting Factors and Biotic Potential _______________________ is a limiting factor whose influence changes with population density Ex: competition, predation, disease __________________ is a limiting factor whose influence is not affected by population density Ex: catastrophic events

Section 3 _________________ is the growth rate of a population under ideal conditions Factors that affect the biotic potential: 1. 2.