Population Ecology Chapter 4 What is ecology Ecology

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Population Ecology Chapter 4

Population Ecology Chapter 4

What is ecology? • Ecology: study of how organisms interact with each other and

What is ecology? • Ecology: study of how organisms interact with each other and their environments

Levels of Organization • Organism: individual living thing • Population: group of individuals of

Levels of Organization • Organism: individual living thing • Population: group of individuals of same species • Community: all species living and interacting together • Ecosystem: living and nonliving things that interact in an area • Biosphere: All living things on earth

Biotic vs. Abiotic Factors • Biotic: things that are living, or used to be

Biotic vs. Abiotic Factors • Biotic: things that are living, or used to be living – Ex: Dead animals, fossil fuels, and plants are all biotic • Abiotic: never been living – Ex: light, oxygen, temperature, wind, etc.

Habitat • Habitat: specific environment in which an organism lives – Like ecosystems, but

Habitat • Habitat: specific environment in which an organism lives – Like ecosystems, but based on a single organism’s living space – Ex: a bug’s entire habitat my be 1 square meter of soil, a vulture’s may be hundreds of square kilometers • Resources: things organisms need to survive – Provided by habitat

Checking Our understanding: 1. Would all the different kinds of organisms in a pond

Checking Our understanding: 1. Would all the different kinds of organisms in a pond be a population, or a community? 2. Would mulch (chopped up tree bark and wood) be biotic or abiotic? 3. Why do different organisms live in different habitats?

Population Size • A species can be made of multiple, separated populations – Humans

Population Size • A species can be made of multiple, separated populations – Humans are so far-spread, we have one giant global population • Population Size: number of individuals present in a population at a given time – Fast decline may mean extinction – Passenger pigeon: used to be most common bird in North America, were hunted to

Measuring Population Size • Sampling: count all organisms in one small area, project answer

Measuring Population Size • Sampling: count all organisms in one small area, project answer to larger area – Works better with stationary things, like plants • Mark and Recapture: trap animals, mark them, release them, wait a long time, recapture and find the ratio of marked and unmarked animals

Population Density • Population Density: the number of individuals within a population per unit

Population Density • Population Density: the number of individuals within a population per unit area – Larger animals usually have lower densities, they need more resources and room to survive • Higher density makes it easier to find mates, but can also lead to more conflict and spread of

Population Distribution • Population Distribution: how organisms are arranged within an area – Random:

Population Distribution • Population Distribution: how organisms are arranged within an area – Random: no pattern, ex: wildflowers – Uniform: evenly spread, ex: nesting penguins each have the same amount of space – Clumped: individuals clump together, most common, ex: schools of fish

Age Structure Diagrams • Age structure describes the relative numbers of organisms of each

Age Structure Diagrams • Age structure describes the relative numbers of organisms of each age within a population – Pre-reproductive – Reproductive – Post-reproductive • Used to predict population growth – Bottom-heavy = rapid growth – Top-heavy = decline – Even = stable

Sex Ratios • Sex ratio: proportion of males to females • Monogamous animals (take

Sex Ratios • Sex ratio: proportion of males to females • Monogamous animals (take only 1 mate) usually have a 50: 50 ratio • Some species imbalanced – Ex. 1 male lion mates with multiple females, more females are born than males

Checking our Understanding 1. How is a population’s size related to its well-being? 2.

Checking our Understanding 1. How is a population’s size related to its well-being? 2. Which population is more dense: 15 flamingos in 5 square meters, or 40 flamingos in 10 square meters? 3. Describe three patterns of population distribution, and name the one that’s most common. 4. Which of the regions below is most likely to grow in size? West Africa Western Europe

Factors that Determine Population Growth • Birth Rates (natality) and Death Rates (mortality) –

Factors that Determine Population Growth • Birth Rates (natality) and Death Rates (mortality) – Expressed as births/death per 1000 organisms per time – If birthrate > death rate, population grows – If death rate > birth rate, population shrinks • Survivorship Curves: graph showing likelihood of dying with age – Type 1 Organisms: Most young survive, most death happens in old age (humans) – Type 2 Organisms: Equal mortality at all ages (birds) – Type 3 Organisms: Many young are killed off, survivors live a long time (sea turtles)

Factors that Determine Population Growth • Immigration (arriving) and Emmigration (leaving) – Animals migrating

Factors that Determine Population Growth • Immigration (arriving) and Emmigration (leaving) – Animals migrating affect local population size

Calculating Population Growth All added individuals – all subtracted individuals (birthrate + immigration rate)

Calculating Population Growth All added individuals – all subtracted individuals (birthrate + immigration rate) – (death rate + emigration rate) • All the above rates are per 1000, and your answer will be per 1000, too • Example: (18 + 5) – (10 + 7) = 6 • That ‘ 6’ means a net increase of 6 individuals per 1000, or 6/1000 • Multiply 6/1000 by 100 to get a percent growth rate. 006 x 100 =. 6% increase

How Populations Grow • Exponential Growth: population grows by a fixed percentage each year

How Populations Grow • Exponential Growth: population grows by a fixed percentage each year – Example: 1000 individuals grow 10% each year. – Year 1: (1000 + 100) = 1100 – Year 2: (1100 + 110) = 1210 – Year 3: (1210 + 121) = 1331 – Year 4: (1331 + 133) = 1464 – Notice rate stays the same, but increase in size grows bigger each year • Graph is J-shaped • Happens in ideal conditions, plentiful resources

How Populations Grow • Logistic Growth: when a population’s initial exponential growth is slowed

How Populations Grow • Logistic Growth: when a population’s initial exponential growth is slowed and stopped by limiting factors – Limiting factors: characteristics of the environment that limit population growth – Ex: Water, space, food, predators, disease – Carrying capacity: largest population size an area can support • S-shaped Graph

How Populations Grow In Nature • Logistic growth is overly simple • Populations overshoot

How Populations Grow In Nature • Logistic growth is overly simple • Populations overshoot carrying capacity, then die off, then rise again • Carrying capacity can change if conditions change – Example: Small plants in the forest get more light after a big tree falls down

Limiting Factors • Either decrease birth rate/immigration, increase death rate/emigration, or both • Density-dependent

Limiting Factors • Either decrease birth rate/immigration, increase death rate/emigration, or both • Density-dependent factors: influence depends on population density – Ex: competition for food, predation, disease • Density-independent factors: influence does not depend on population density – Ex: Catastrophic events like floods and fires, climate change

Biotic Potential • Biotic potential: maximum ability to produce offspring in ideal conditions –

Biotic Potential • Biotic potential: maximum ability to produce offspring in ideal conditions – Gestation time: how long for fetus to develop and be born – Generation time: time from birth until organism can have its own offspring – Number of offspring born at once • Ex: Scorpion fish reach maturity at 3 -4 years of age, then release 100, 000 eggs/year. Orangutans reach maturity at 10 years, and have 1 baby every 8 years. • Populations with high biotic potential can grow faster than those with low biotic potential

Checking Our Understanding 1. A population has a birthrate of 10/1000, a death rate

Checking Our Understanding 1. A population has a birthrate of 10/1000, a death rate of 9/1000, an immigration rate of 3/1000, and an emigration rate of 7/1000. What is the population’s growth rate? Is it getting bigger or smaller? 2. What’s the difference between exponential and logistic growth? Which is more common in nature? 3. In your own words, define ‘limiting factor’ and ‘biotic potential’.