APES Exam Review

Over Unit 6, Unit 7, & Unit 9

Order of Ecology

organism → population → community → ecosystem → biosphere

Organism

individual living thing

Population

group of individuals of same species living together/interacting

Community

several populations of different organisms living & interacting with each other

Ecosystem

communities of organisms interacting with each other & nonliving environment

Biosphere

areas of Earth where life exists

Population dynamics/ecology

study of how populations can increase or decrease in size

You determine population dynamics

—Size, Density, Distribution, Sex ratio, Age structure

Size (N)

number of individuals

Density

number of individuals in a given area

Distribution

how individuals are spread out over their area

Distribution forms

Random, uniform, or clumped

Sex ratio

ratio of males to females

Age structure

number of individuals that are in different age categories

3 major Age structure categories

pre-reproductive, reproductive, post reproductive

Limiting Factor

resources that population cannot live without; exists at lower levels than needed for population to increase

Examples of limiting factors

For animals: food & water. For plants: soil, light, water

Carrying capacity (K)

The maximum population of a species that an area can maintain indefinitely

• Dependent on limiting factors 

• The population growth rate often decreases as population size approaches K 

Density-dependent population controls

Effect on population varies based on density of population

• Eg. disease: will affect dense populations more; Food availability

Density-independent population controls

Affect populations the same regardless of its density

—Eg Temperature, natural disasters, pollution

Intrinsic growth rate (r)

Maximum growth rate of population under ideal conditions

—High births, few deaths

—With high r and ideal conditions, can see exponential growth

Forms J-shaped curve in graph

Logistic growth

Exponential growth followed by decrease in growth and then leveling off of population near K

—Due to limiting factors

—S-shaped curve

—Overshoot- when population increases past K

—Can then experience die off/collapse

K-selected species

—Have a low r (Intrinsic growth rate)

—Larger organisms reproduce later in life, few (but large) offspring, have a long life span, mature slowly, high levels of parental care

—K-selected mammals- longer gestation period

—Population levels off as it approaches K– follows logistic curve

—More prone to extinction

—Eg elephants, humans, whales, raptors, sharks, some plants

r-selected species

—Have a high r

—Small organisms, have many small offspring, little or no parental care, mature quickly

—Tend to be opportunists – reproduce and spread rapidly when conditions are ideal or niche opens up

—Go through boom and bust cycles- overshoot K followed by die-off

—Eg rats, insects, algae, bacteria

Survivorship curve

Show patterns of survival of species over their lifetime

Habitat islands-

isolated habitats (often containing populations) surrounded by human settlement/activity

—Often caused by habitat fragmentation

—Can lead to changes in species diversity, genetic diversity (inbreeding)

Inbreeding depression

Inbreeding depression

lowering fitness (how well they survive and reproduce) of a population through the mating of genetically similar individuals (often relatives)

Habitat/wildlife corridors

can connect isolated habitats

—Can be natural or manmade

—E.g., Jaguar corridor initiative

—Can increase diversity, reduce inbreeding

—Metapopulation

Metapopulation

separated populations that are occasionally connected by species movement

Interspecific competition

competition for limited resources between different species 

—Eg food, water, light, space

—Competitive exclusion principle

—No two species can occupy exactly the same niche

—Resource partitioning (aka niche differentiation)

Competitive exclusion principle

species competing for same resources cannot coexist 

• No two species can occupy exactly the same niche

Niche

the specific functional role and position a species has within its ecosystem, encompassing all the physical, chemical, and biological factors it requires to survive and reproduce

Resource partitioning (aka niche differentiation)

species evolve (eg change behavior, morphology) to reduce niche overlapping /competition

Predation

When one animal kills and consumes another

Prey have evolved ways to avoid predation:

Physical, Chemical, & Behavioral

Ways Prey have evolved to avoid predation:

Physical:

Camouflage, acute senses (smell, sight, etc.), speed, physical protection (eg, spines, thorns), aposematic (warning) coloration, mimicry

Chemical

oBad tastes/odor, irritating defenses (eg, skunk), poisonous to consume

Behavioral:

oClumping behavior (herding, schooling)

Parasitism

When a species lives on or in another and causes it harm

—Feeds on, uses the energy of another organism

—A parasite is usually smaller and often does not kill the host

• Pathogen

Pathogen

organism that causes disease in host

—Eg Many types of bacteria & viruses

Herbivory

When consumer feeds on a producer

—Usually only eat part of producer without killing whole organism

Mutualism

Species interaction in which both species benefit

—Survival and reproduction chances of both improve

—Most species involved in some kind(s) of mutualism

Commensalism

—Species interaction where one species benefits, other is not benefitted or harmed

Keystone species

Species that has large effects on its ecosystem

—Organism is usually not very abundan

• Types of keystone species:

• Predators: Eg, gray wolf, jaguar, sea otter

• Foundation species: E.g. grizzly bear, beaver, prairie dog, elephants

Predators

keep populations of prey species lower → can benefit other species

• Top Predators are a type of keystone species because they cause the trophic cascade to happen

—Eg gray wolf, jaguar, sea otter

Foundation species

ecosystem engineers; physically alter ecosystems in ways that can benefit other species

—E.g. grizzly bear, beaver, prairie dog, elephants

Ecological succession

predictable replacement of groups of species with others over time

—Follows an expected progression

—Focuses on plants/producers

Primary succession

form of succession in which ecosystem forms where no soil or bottom sediment existed before

—“Start from scratch” ecosystem

—Eg Volcanic area, abandoned parking lot, new islands

—Rock weathers (breaks down) physically & chemically – forms some constituents of soil

Pioneer species arrive

Pioneer species

eg mosses, lichens, ferns

—Grow on rock → decompose and mix with rock to form soil

—Followed by mid and late successional plants (larger)

Soil

made of bits of rock & organic matter

Secondary Succession

ecosystem forms where soil or bottom sediment already exists → resilience (ability to bounce back)

• Ecosystems w/ high resilience are more likely to undergo secondary succesion

—Often seen as nature “reclaiming” an area

—Ecosystem existed there previously

—Eg Burned or cut forest, abandoned farmland, polluted or altered waterways, vacant lots

—Occurs in similar way to primary succession – smaller plants become established & larger ones eventually move in

Ecosystems influenced by _____, _____, _____, & _____ from other ecosystems 

Latitude, Time, Size, & Distance 

Latitude

closer to equator = more biodiversity

—Eg tropical rainforest vs. tundra

Time

older ecosystem = more biodiversity

—More time for speciation, species immigration to occur

Size

larger ecosystem = more biodiversity

—More species can exist in larger places

—Larger places more are resistant to disaster, extinctions

—Species more likely to move into larger areas

—Larger places have more niches

Distance

closer to other ecosystem = more biodiversity

Eg islands closer to the mainland vs. those that are more isolated

Human population has grown _____ throughout most of history BUT has experienced exponential ______ over the past 200 years ( __ shaped curve)

slowly, growth, J

Why has the earth experienced such a rapid growth recently?

1. Ability of humans to spread into all areas of Earth   

—Regardless of habitat, climate

2. Improved agricultural techniques

—More food production

—Better access to necessary nutrients

3. Improved public health

—Medicines, vaccines, antibiotics

—Sanitation, water treatment

Malthusian theory

Belief that human population growth will outpace food production

Demography

study of human population and population trends

—Crude birth rate

—Crude death rate

Doubling time

amount of time it takes for a population to double in size

—DT (years) = 70/growth rate (as a percent

Crude birth rate

number of births per 1000 individuals

Crude death rate

number of deaths per 1000 individuals

Global population growth rate

= (CBR – CDR)/1000

Total fertility rate

the average number of children woman has in her life

—Declining worldwide

—Global TFR in 2020 → 2.4 

—Higher TFR in developing countries

Replacement-level fertility rate

fertility rate required in order to offset deaths; Fertility rate needed for population to remain stable

—Approx. 2.1 in developed countries, higher in developing countries

Life Expectancy

average number of years people live in a given time/place

—2019 → 72 years worldwide (higher for women than men)

—Generally increasing worldwide

—2019 → 79 years in U.S.

—Generally higher in other developed countries than U.S. (#38 in world)

Infant mortality rate

number of deaths of children under age of 1 per 1000 live births

—IMR lower in other developed countries than U.S. (56^th lowest in world)

• higher in developing countries

• generally decreasing worldwide

Child mortality rate

number of deaths of children under age of 5 per 1000 live births

• higher in developing countries

• generally decreasing worldwide

HIV/AIDS

—Killed 30 million people between 1990-2015

—8 African countries have HIV infection of 10-28%

—Caused reversal of positive demographic trends (eg life expectancy)

—Has removed large numbers of young adults from populations of countries → continues state of poverty

—Decrease in number of workers → less productivity, less support for young and old

Immigration in the U.S

1820 – present → U.S. has taken in 2x as many immigrants as all other countries combined

—Currently, 40% of population growth due to immigration

—Until 1960, most came from Europe

—Since 1960, most come from Latin America & Asia

• Net migration rate

—Despite low fertility rates (below replacement), U.S. (& Canada) is one of few developed countries with growing population

—Problematic: ecological footprint of average American is very high

Net migration rate

(immigration – emigration) per 1000 people

—U.S. – 3 immigrants per 1000 people

Migration (immigration & emigration)

—Most occurs due to people seeking economic opportunity

—Some people migrate as refugees of war, ethnic & religious persecution, political oppression

—Number of environmental refugees increasing

—Eg lack of water, food, rising seas

—25 million in 2005

—Approx. 50 million in 2010

Top ten countries by population size:

—1. China

—2. India

—3. U.S.

—4. Indonesia

—5. Pakistan

—6. Brazil

—7. Nigeria

—8. Bangladesh

—9. Russia

—10. Mexico

Age structure

distribution of ages of people of population

Age structure diagram

(aka population pyramid) shows percentages/numbers of males & females in population

—Breaks them down into five year increments

—3 major categories of ages:

—Pre reproductive, reproductive (15-44), post reproductive