CHAPTER 4 Population Ecology
Chapter 4 TOPIC POPULATION ECOLOGY
Indicator Species Serve as Biological Smoke Alarms Indicator species Provide early warning of damage to a community Can monitor environmental quality Trout Birds Butterflies Frogs
Case Study: Monteverde Golden Toad Talk About It Why is the extinction of the golden toad a global concern? INDICATOR SPECIES Golden toads lived in Costa Rica s Monteverde cloud forest. Golden toads were first described in 1964. They were extinct by 1989. WHY?? Drier days pools and ponds dried up nowhere to lay eggs Warming Oceans cloud elevation higher drying out the rainforest Warmer nights increased growth of fungi that infected the frog skin What other factors may cause frog extinction??
Case Study: Why Are Amphibians Vanishing? (1) Habitat loss and fragmentation Prolonged drought Pollution Increase in UV radiation Parasites Viral and fungal diseases Climate change Overhunting Nonnative predators and competitors
Case Study: Why are Amphibians Vanishing? Fast Track pg 97 Frogs serve as indicator species because different parts of their life cycles can be easily disturbed. Figure 7-3
Many Costa Rican frogs are so specialized, that they have learned to survive in the canopies of trees by using the water that's deposited in bromeliads and tree trunks; this way, they don't have to descend to the ground and risk being attacked by predators or of their tadpoles being eaten by fish.
Tropical frogs are probably one of the most sensitive animals in the world and react very rapidly to substantial changes in their environments. They also form vital parts of the ecosystems to which they belong. That is why they are considered "an indicator species" - the species that "indicate" the state of the health of their ecosystems.
The frogs' disappearance could cause loss of control over some populations of insects and could let them grow in numbers, or it could be the cause of reduction in the quantity of food for other forest animals feeding on frogs etc.
Tropical Rain Forests Are Disappearing Cover about 2% of the earth s land surface Contain about 50% of the world s known plant and animal species Disruption will have three major harmful effects Reduce biodiversity Accelerate global warming Change regional weather patterns
Lesson 4.1 Studying Ecology Levels of Ecological Organization The study of how organisms interact with each other and with their environments Scientists study ecology at various levels of organization.
Biosphere Parts of the earth's air,water, and soil where life is found Ecosystem A community of different species interacting with one another and with their nonliving environment of matter and energy Community Populations of different species living in a particular place, and potentially interacting with each other Population A group of individuals of the same species living in a particular place Organism An individual living being Cell The fundamental structural and functional unit of life Water Hydrogen Oxygen Molecule Atom Chemical combination of two or more atoms of the same or different elements Smallest unit of a chemical element that exhibits its chemical properties Stepped Art Fig. 3-5, p. 58
Lesson 4.1 Studying Ecology Biotic and Abiotic Factors Biotic factors: Parts of an ecosystem that are living or used to be living Abiotic factors: Parts of an ecosystem that have never been living Water Air Nutrients Rocks Heat Solar energy Did You Know? Decaying organisms are biotic factors as long as their structure remains cellular.
Major Biotic and Abiotic Components of an Ecosystem Fig. 3-6, p. 59
Lesson 4.1 Studying Ecology Habitat The specific environment in which an organism lives Habitats provide an organism with resources anything an organism needs to survive and reproduce, including food, shelter, and mates.
Lesson 4.2 Describing Populations From 1900 to 2000, the white-tailed deer population of New York state grew from about 20,000 to more than 1 million. Densities of more than 100 deer per sq mi occur in some metropolitan areas.
Lesson 4.2 Describing Populations Population Size The number of individuals in a population at a given time Sudden and dramatic decreases in population size can indicate an unhealthy population headed toward extinction. Ecologists often use sampling techniques to estimate population size. Did You Know? The passenger pigeon was once North America s most abundant bird. Hunting drove them to extinction in less than 100 years. Counting Laysan Albatross Nests
Lesson 4.2 Describing Populations Population Density Measure of how crowded a population is Larger organisms generally have lower population densities. Low population density: More space, resources; finding mates can be difficult High population density: Finding mates is easier; tends to be more competition; more infectious disease; more vulnerability to predators Northern pintail ducks
Lesson 4.2 Describing Populations Population Distribution How organisms are arranged within an area: Random distribution: Organisms arranged in no particular pattern QuickTime and a decompressor are needed to see this picture. Uniform distribution: Organisms evenly spaced QuickTime and a decompressor are needed to see this picture. Clumped distribution: Organisms grouped near resources; most common distribution in nature QuickTime and a decompressor are needed to see this picture.
Generalized Dispersion Patterns Fig. 5-12, p. 112
Why clumping??? Resources a species needs vary greatly in availability Protection from predators Gives predatory species a better success rate when hunting Temporary groups for mating and care of young (a) Clumped (elephants) Fig. 8-2a, p. 162
Why uniform distribution? Usually found when resources are scare but evenly spread out over an area Helps to reduce intraspecific competition over scarce resources (b) Uniform (creosote bush) Fig. 8-2b, p. 162
Why random??? Rarely occurs in nature. Will only occur when resources are fairly high and spread out over a large area. (c) Random (dandelions) Fig. 8-2c, p. 162
Lesson 4.2 Describing Populations Relative number of organisms of each age group within population Age Structure Can be used to predict future population growth of a population
Lesson 4.2 Describing Populations Sex Ratios Proportion of males to females Age structure diagrams give information about sex ratios. For a monogamous species, the ideal sex ratio is 50:50.
Lesson 4.3 Population Growth From 1800 to today, the human population has grown from about 1 billion to more than 6.8 billion an exponential rate of increase.
Populations Can Grow, Shrink, or Remain Stable Population size governed by Births Deaths Immigration Emigration Population change = (births + immigration) (deaths + emigration)
Lesson 4.3 Population Growth Immigration and Emigration In addition to births and deaths, population growth is affected by immigration and emigration individuals moving into and out of a population. Migration, seasonal movement into and out of an area, can temporarily affect population size.
Lesson 4.3 Population Growth Calculating Population Growth Determined by the following equation: (birthrate + immigration rate) (death rate + emigration rate) Growing populations have a positive growth rate; shrinking populations have a negative growth rate. Usually expressed in terms of individuals per 1000 Did You Know? Immigration contributes more than 1 million people to the U.S. population per year. QuickTime and a decompressor are needed to see this picture.
Lesson 4.3 Population Growth Biotic Potential An organism s maximum ability to produce offspring in ideal conditions Many factors influence biotic potential, including gestation time and generation time. Organisms with high biotic potential can recover more quickly from population declines than organisms with low biotic potential.
Lesson 4.3 Population Growth Birth and Death Rates A population s relative birth and death rates (mortality and natality) affect how it grows. Survivorship curves show how the likelihood of death varies with age. QuickTime and a decompressor are needed to see this picture. The way to represent the age structure of a population is with a survivorship curve. Late loss population live to an old age. Constant loss population die at all ages. Most members of early loss population, die at young ages.
Species Have Different Reproductive Patterns Type III Some species Many, usually small, offspring Little or no parental care Massive deaths of offspring Insects, bacteria, algae
Species Have Different Reproductive Patterns Type I Other species Reproduce later in life Small number of offspring with long life spans Young offspring grow inside mother Long time to maturity Protected by parents, and potentially groups Humans Elephants
Late loss Early loss Age
Lesson 4.3 Population Growth Logistic Growth and Limiting Factors Growth almost always slows and stops due to limiting factors. Limiting factors: Environmental characteristics slow population growth and determine carrying capacity. Density-dependent: Influence changes with population density. Density-independent: Influence does not change with population density.
Under Some Circumstances Population Density Affects Population Size Density-dependent population controls WAR DISEASE - FAMINE Predation Parasitism Infectious disease Competition for resources
Lesson 4.3 Population Growth Population increases by a fixed percentage every year. Exponential Growth Normally occurs only when small populations are introduced to an area with ideal environmental conditions QuickTime and a decompressor are needed to see this picture. Rarely lasts long