R 4 Population Ecology - Biology- Discover Life!

4 Population Ecology C

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Lesson 4.1 Studying Ecology

Ernst Haeckel defined ecology in 1866 as “the body of knowledge concerning the economy of nature—the total relations of the animal to both its inorganic and organic environment.”

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.


Levels of Ecological Organization

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


Did You Know? Decaying organisms

are biotic factors as long as their

structure remains cellular.

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.

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

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

Population Distribution


• How organisms are arranged within an area:

• Random distribution:

Organisms arranged in

no particular pattern

• Uniform distribution:

Organisms evenly spaced

• Clumped distribution:

Organisms grouped near resources;

most common distribution in nature.

Age Structure


• Relative number of organisms of each age group

within population

• Can be used to predict future population growth of a

population

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.

Calculating Population Growth


• A population’s relative birth and death rates (mortality and

natality) affect how it grows.

• Determined by the following equation:

(birthrate + immigration rate) – (death rate + emigration rate)

• (13) - (16)= -3/1000

• Growing populations have a positive growth rate.

• Shrinking (declining) 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.

Birth and Death Rates


• Survivorship curves show

how the likelihood of death

varies with age.

• Type I: Most young survive,

mortality rates are high in

old age.

• Type II: Equal mortality

rates at all ages.

• Type III: Many offspring are

produced with few surviving

to adulthood. Death is less

likely at an older age.

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.

Exponential Growth


• Population increases by

a fixed percentage

every year.

• Normally occurs only

when small populations

are introduced to an

area with ideal

environmental conditions

• Rarely lasts long

Logistic Growth and Limiting Factors


• The growth curve shows an increase at first, but stabilizes to

the carrying capacity due to limiting factors.

Logistic Growth and Limiting Factors

• Limiting factors: Environmental characteristics slow population growth and determine carrying capacity.

• Density-dependent: Influence changes with population density.

Ex: Food, Disease, predators

• Density-independent: Influence does not change with population density.

Ex: Climate change, drought, flood

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 5.3 Ecological Communities

The sun provides the energy for almost all of the ecological communities and species interactions on Earth.

Primary Producers (Autotrophs) • Capture energy from the sun or

from chemicals and store it in the bonds of sugars, making it available to the rest of the community

• Energy from the sun is captured by plants, algae, or bacteria through photosynthesis.

• Energy from chemicals is captured by some bacteria through chemosynthesis.


Did You Know? Deep-sea vents, far from sunlight, support entire communities of fish, clams, and other sea animals, which depend on energy converted through chemosynthesis.

Consumers (Heterotrophs) •Rely on other organisms for energy and nutrients

• Herbivores: plant-eaters

• Carnivores: meat-eaters

• Omnivores: combination-eaters

• Detritivores and decomposers: recycle nutrients within the ecosystem by breaking down nonliving organic matter

•Use oxygen to break bonds in sugar and release its energy through cellular respiration (primary producers do this, too)


California Condor

Did You Know? Scavengers, such as vultures and condors, are just large detritivores.

Energy in Communities • An organism’s rank in a

feeding hierarchy is its trophic level.

• Primary producers always occupy the first trophic level of any community.

• In general, only about 10% of the energy available at any trophic level is passed to the next; most of the rest is lost to the environment as heat.


Pyramid of Energy

Numbers and Biomass in Communities

• A trophic level’s biomass is the mass of living tissue it contains.

• In general, there are more organisms and greater biomass at lower trophic levels than at higher ones.


Food Chains and Webs

• Food web: Shows the overlapping and interconnected food chains present in a community


• Food chain: Linear series of feeding relationships

• Species that have strong and/or wide-reaching effects on a community

• Removal of a keystone species can significantly alter the structure of a community.

Keystone Species


Invasive Species

Lesson 5.4 Community Stability

•Nonnative organisms that spread widely in a community

• A lack of limiting factors such as predators,

parasites, or competitors enables their

population to grow unchecked.

• Not all invasive species are harmful.

Did You Know? Although the European honeybee is

invasive to North America, it is beneficial because it

pollinates our agricultural crops.

Lesson 5.2 Species Interactions

The zebra mussel has completely displaced 20 native mussel species in Lake St. Clair.

The Niche


• Describes an organism’s use of resources and functional

role in a community

• Affected by an organism’s tolerance—its ability to survive

and reproduce under changing environmental conditions

• Often restricted by competition

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.


Competition • Organisms compete when

they seek the same limited resource.

• In rare cases, one species can entirely exclude another from using resources.

• To reduce competition, species often partition resources, which can lead to character displacement.


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Resource Partitioning

Predation (+/–)

• The process by which a predator hunts, kills, and consumes prey

• Causes cycles in predatory and prey population sizes

• Defensive traits such as camouflage, mimicry, and warning coloration have evolved in response to predator-prey interactions.

• Some predator-prey relationships are examples of coevolution, the process by which two species evolve in response to changes in each other.


Did You Know? A single rough-skinned newt contains enough poison to kill 100 people. Unfortunately for the newt, its predator, the common garter snake, has coevolved resistance to the toxin.

Rough-Skinned Newt

Parasitism and Herbivory (+/–)


Did You Know? One study of Pacific estuaries suggests that parasites play an important role in keeping these ecosystems healthy by controlling host populations.

Hookworm (a parasite)

• Parasitism: One

organism (the parasite)

relies on another (the

host) for nourishment or

for some other benefit

• Herbivory: An animal

feeding on a plant

Mutualism (+/+) and Commensalism (+/0)


Did You Know? Symbiosis describes a long-lasting and physically close relationship between species in which at least one species benefits.

• Mutualism: a

relationship in which two

or more species benefit

• Commensalism: a

relationship in which one

species benefits while

the other is unaffected Lichen: a symbiotic relationship between a

fungus and a photosynthetic partner, such as

an alga


A 2010 report on invasive species suggests that they cost the U.S. $120 billion a year in environmental losses and damages.

Invasive kudzu

Ecological Disturbances


• A community in equilibrium is generally stable and balanced, with most populations at or around carrying capacity.

• Disturbances or changes in the environment can throw a community into disequilibrium.

• Severe disturbances can cause permanent changes to a community and initiate a predictable series of changes called succession.

Forest fire

Primary Succession


• Occurs when there are no traces of the original community remaining, including vegetation and soil

• Pioneer species, such as lichens, are the first to colonize.

• The environment changes as new species move in, adding nutrients and generating habitat.

Secondary Succession


• Occurs when a disturbance dramatically alters a community but does not completely destroy it

• Common after disturbances such as fire, logging, or farming

• Occurs significantly faster than primary succession

Succession in Water


• Primary aquatic succession occurs when an area fills with water for the first time.

• Disturbances such as floods or excess nutrient runoff can lead to secondary aquatic succession.

Climax Communities


• Ecologists once thought succession leads to stable “climax” communities.

• Today, ecologists see communities as temporary, ever-changing associations of species.

• Communities are influenced by many factors and constant disturbances.

Beech-maple forest, a classic “climax community”

Lesson 5.1 Evolution

Scientists have identified and described over 1.5 million species. Millions more have yet to be discovered.

Evolution and Natural Selection

• Gene: A sequence of DNA that codes for a particular trait

• Gene pool: All the genes present in a population

• Biological evolution: The change in a population’s gene pool over time




Mechanisms of Biological Evolution: Mutation and Migration

Mutation


Accidental change in DNA

that can give rise to

variation among individuals

Migration (gene flow)

Movement of individuals into

(immigration) or out of (emigration)

a population

Mechanisms of Biological Evolution: Genetic Drift and

Natural Selection


Genetic Drift Natural Selection

Evolution that occurs by chance Process by which traits useful for survival and reproduction are passed on more frequently than those that are not

Conditions of Natural Selection


(1) Organisms

produce more

offspring than can

survive.

(2) Individuals vary in

characteristics, some

of which are heritable.

(3) Individuals vary in

fitness, or reproductive

success.

Did You Know? Darwin privately researched natural selection for two decades before publishing On the Origin of Species.

Artificial Selection


• Selection under human direction

• Throughout history, humans have chosen and bred

animals and plants with beneficial traits.

Speciation




• Process by which

new species are

generated

• Can occur in a

number of different

ways; the most

important way is

called allopatric

speciation

• Has resulted in every

form of life on Earth—

today and in the past

Allopatric Speciation

Extinction


• The disappearance of

species from Earth

• Generally occurs gradually,

one species at a time,

when environmental

conditions change more

rapidly than the species

can adapt

• There are five known mass

extinction events, each of

which wiped out a large

proportion of Earth’s

species.

Did You Know? During the Permo-Triassic

extinction 250 million years ago, 70% of all

land species and 90% of all marine species

went extinct.

Trilobites

Marine arthropods that went extinct at the

end of the Permian period.

Lesson 6.1 Defining Biomes

Fossil evidence suggests that the frozen continent of Antarctica was once covered in temperate forest.

Earth’s Major Biomes

• Groups of terrestrial

ecosystems that

share biotic and

abiotic conditions

• 10 primary biomes:

• tropical rain forest

• dry forest savanna

• desert

• temperate rain forest

• temperate forest

• temperate grassland

• chaparral

• boreal forest

• tundra Did You Know? Taiga is another

name for boreal forest.


Climate and Climatographs

• Climate: Average conditions,

including temperature and

precipitation, over long periods

of time in a given area

• Weather: Day-to-day conditions

in Earth’s atmosphere

• Climatographs: Diagrams that

summarize an area’s average monthly

temperature and precipitation

• Each biome has a set of characteristic

organisms adapted to its particular

climate conditions.


Biomes and Net Primary Production •Gross primary production: The rate at which primary

producers undergo photosynthesis

•Net primary production: The amount of organic matter (biomass) that remains after primary producers use some to carry out cellular respiration

• Ecosystems vary in their net primary productivity, the rate at which primary producers convert energy to biomass.

•Warm, wet biomes generally have higher net primary productivity than cold, dry biomes.


Lesson 6.2 Biomes

Tundra, found at very high latitudes, is nearly as dry as a desert.

Savanna

Lesson 6.2 Biomes

• Receives less precipitation than tropical

dry forests, but more than deserts; usually

has a distinct rainy season

• Grasses interspersed with groups of trees

• Tree growth limited by frequent fires and

strong winds

• Plants are adapted to dry conditions; tend

to be deciduous with deep roots, thick

bark, and waxy coatings on leaves.

• Many animals migrate to find water, or

burrow when water is scarce.

Desert

Lesson 6.2 Biomes

• Receives less than 25 cm (9.8 in.)

of precipitation per year

• Temperatures vary widely from

day to night.

• Plants tend to have thick, leathery

leaves, store water in their tissues,

and have shallow roots.

• Animals get most of their water

from the food they eat, and they

tend to be nocturnal. Mammals

have exaggerated appendages to

help regulate body temperature.

Did You Know? Cactus spines are modified leaves that protect the plant from thirsty animals. Photosynthesis occurs within the green stems and trunks.

Temperate Forest

Lesson 6.2 Biomes

• Precipitation evenly spread

throughout the year

• Varied temperatures (hot

summers, cold winters)

• Plants tend to be broad-leafed and

deciduous.

• Soil is enriched with nutrients from

annual leaf drop.

• Animals may migrate, hibernate,

or store food to survive cold

conditions.

Temperate Grassland (Prairie)

Lesson 2.2 Biomes

• Moderate seasonal precipitation and fairly

extreme seasonal temperatures; droughts and

fires common

• Not enough precipitation to support large trees;

grasses, which grow from their base, thrive

despite droughts, fires, animals grazing

• Animals are adapted to deal with lack of cover.

• Soil tends to be rich in nutrients; most of world’s

grasslands have been converted to farmland.

Chaparral

Lesson 6.2 Biomes

• Highly seasonal conditions with mild,

wet winters and warm, dry summers

• Prolonged hot, dry periods; droughts and fires common

• Plants are drought-resistant; many have thick, waxy

leaves or leaves with hairs that trap moisture;

succulents are common.

• Plants may have thick bark and

deep roots to resist fire; some plants

require fire to germinate.

• Many animals burrow or are nocturnal

to avoid heat.

Did You Know? Some

chaparral plants contain

oily compounds that

facilitate the spread of fire.

Lesson 6.3 Aquatic Ecosystems

75% of Earth’s surface is covered by water.

Describing Aquatic Ecosystems


• Salinity: the amount of dissolved

salt present in water. Ecosystems

are classified as salt water, fresh

water, or brackish depending on

salinity.

• Photosynthesis tends to be limited

by light availability, which is a

function of depth and water clarity.

• Aquatic ecosystems are either

flowing or standing.

• Aquatic ecosystem zones: photic,

aphotic, benthic

Freshwater Ecosystems: Ponds, Lakes, Inland Seas


• Salinity is less than 0.5 ppt (parts per thousand)

• Ponds and lakes are

similar, except in size,

but inland seas contain

organisms adapted for

open water.

• Ponds and lakes are

divided horizontally

into zones: littoral

and limnetic

Freshwater Ecosystems: Wetlands


• Areas of land flooded with water at least part of the year

• Include freshwater marshes, swamps, bogs, and fens

• Wetlands prevent flooding, recharge aquifers, filter pollutants,

and provide habitats.

Tropical Rain Forest

Lesson 6.2 Biomes

• Year-round warm temperatures

and at least 2 m (6.6 ft)

precipitation a year

• Soil generally nutrient-poor

• Forest canopy, emergent layer,

and understory support enormous

variety of plants.

• Plants tend to have large, flat

leaves and shallow roots.

• Supports more animal species

than any other biome; animals

tend to be highly specialized.

Did You Know? Some tropical plants (epiphytes) grow high on other plants to access sunlight and do not touch the soil.

Tropical Dry Forest

Lesson 6.2 Biomes

• Warm year-round, but rainfall

highly seasonal

• Most trees are deciduous—they

lose their leaves and cease

photosynthesis part of the year.

• Plants and animals exhibit

adaptations (e.g. waxy leaf

coating, deep roots, estivation,

migration) that enable them to

survive the dry season.

Tiger (Panthera tigris)

Temperate Rain Forest

Lesson 6.2 Biomes

• Year-round moderate temperatures and heavy rainfall

• Largest extent found in Pacific Northwest of United States

• Characterized by tall evergreen trees, such as cedars and

hemlocks, that don’t lose leaves annually; many are conifers

(produce seed-bearing cones)

• Forest floor is shaded,

damp, covered in moss.

• Animals that require

moisture, such as

amphibians, thrive here.

Olympic Peninsula, Hoh River rain forest

Boreal Forest (Taiga)

Lesson 6.2 Biomes

• Long, cold winters; short,

cool summers

• Nutrient-poor, slightly

acidic soils

• Low species diversity

• Coniferous trees with

waxy needles and conical

shape, adapted to harsh, snowy conditions are common.

• Animals feed, breed, and care for young mostly during

short warm season; year-round residents tend to have thick

insulation and small extremities that maintain heat.

Tundra

Lesson 6.2 Biomes

• Extremely cold, dark winters; relatively sunny and cool

summers

• Found at very high latitudes in the Northern Hemisphere

• Harsh winds, nutrient-poor soil, and freezing temperatures

limit plant growth; no tall trees; mosses and lichens common

• Characterized by permafrost (underground soil that is frozen

year-round)

• Birds and caribou migrate to the

tundra during the mild summer to

feed on insects and lichens; only a

few species live here year-round.

Polar Ice and Mountains

Lesson 6.2 Biomes

• Not classified as biomes

• No land under polar ice in

Northern Hemisphere; ice sits

atop Antarctica in Southern

Hemisphere

• Very few plants; most life

is in surrounding ocean

• Mountain communities

change with elevation,

similar to how biome

communities change

with latitude.



Freshwater Ecosystems: Rivers and Streams


• Bodies of surface water that flow

downhill, eventually reaching an

ocean or inland sea

• Watershed: The area of land

drained by a river and its tributaries

• Characteristics, such as dissolved

oxygen, temperature, water speed,

organisms, and others, change

from source to mouth.

Estuaries


• Occur where a river flows into the

ocean or an inland sea

• Coastal estuaries are brackish

ecosystems; organisms must tolerate

wide salinity and temperature ranges.

• Coastal estuaries are home to salt

marshes and mangrove forests.

• Like wetlands, estuaries help prevent

flooding and soil erosion as well as

provide habitats.

Did You Know? Salt marshes and mangrove forests are

two of the most productive ecosystems on Earth.

Everglades, Florida, wetlands

Oceans


• Currents are driven by water temperature and density

differences, wind, and gravity.

• Surface winds and heating generate vertical currents that

transport nutrients and oxygen.

Did You Know? If the water in the

oceans evaporated, a 60 m (200 ft) deep

layer of salt would be left behind.

• Horizontal ocean zones:

intertidal, neritic, open

ocean

• Vertical ocean zones:

photic, aphotic, benthic



Ocean Ecosystems


• Intertidal: Highly diverse; extreme range of temperature, moisture, and salinity

• Neritic: Productive kelp forests and coral reefs provide habitats and help protect shorelines from erosion.

Did You Know? Over 90% of ocean water

on Earth is in the open ocean zone.

• Open ocean: Low productivity due to low light penetration; phytoplankton base of food chain; deep sea organisms and hydrothermal vent communities

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R 4 Population Ecology - Biology- Discover Life!