Chapter 25 Populations and Ecosystems

Concepts

Individuals never

exist in isolation

a habitat

instead

there are other individuals

makes up a population

often do not interact strongly

if dioecious or self-sterile

carries out successful sexual reproduction

individuals cannot

can sustain

a population of pollinators

can be more susceptible to

pathogens

catastrophes

predators

population does not exist

in isolation

but rather

coexists with other populations

constitutes a community

when put together with

physical, nonliving environment

make up a ecosystem

Plants in Relationship to Their Habitats

Abiotic Components of the Habitat

Climate

important to

all organisms

many organisms restricted to

certain climate regions

many components

temperature

rainfall

relative humidity

winds

extremes are important

determine what plants can

live in that region

examples

many

bromeliads

aroids

orchids

restricted to tropics

frost free habitats

many temperate trees

need subfreezing temperatures

to be vernalized and bloom

growing season determined by

last killing frost in spring

and

first killing frost of autumn

must be adequate for

sufficient photosynthesis

growth development

reproduction

seasonal extremes most important

tolerance range

range of extremes that

certain plant can survive in

Soil Factors

soils formed by

breakdown of rock

pioneers

first plants to

invade new soil

in most tolerate severe conditions

soil conditions

sandy

large particle size

most minerals still locked

in the rock matrix

little water holding capacity

associated with nitrogen-fixing prokaryotes

change soil significantly

soil profile

3 distinct horizons

A horizon

AKA zone of leaching

consists of

litter

debris

B horizon

AKA zone of deposition

was nutrients into

B horizon

materials accumulate

from A horizon

rich in nutrients

contains

clay

humus

C horizon

composed mostly of

parent rocks

rock fragments

Disturbance

phenomena

examples

fires

landslides

snow avalanches

floods

produce significant radical change

in an ecosystem

affect

biotic factors directly

usually eliminate

all or most plants

plants can become

fire resistant

caused by

frequent fires

Biotic Components of the Habitat

The Plant Itself

can modify habitat

can be

beneficial

detrimental

neutral

Examples

Beech/Oak trees

create dense canopies

helps seedlings grow faster

Other Plant Species

Individuals occurring together

create interaction

can cause

mutualism

both plants benefit

competition

disadvantageous for plants

plants compete for

same materials

such as

light

soil nutrients

water

attention of pollinators

seed dispersers

Competitive exclusion

whichever species is less adapted

is excluded from ecosystem

first theory

Second Theory

Species overlap in tolerance range

weaker species occupies partial niche

Geographic range

can be very extensive

creates ecotypes

same species but

different ways of competing

which species is weaker

can depend on

what type of severe weather

is occurring

Organisms Other than Plants

Animals Fungi and Prokaryotes

can have interrelationships with plants

Mutualism

example

Ants and acacias

ant gets

food

housing

acacias get

protection

from

predators

competition

Commensal Relationship

one benefits/negative effect

and

other is unaffected

example

birds nesting in trees

Predation

one benefits

and

the other is harmed

example

herbivory

browsing

eating

twigs and leaves

grazing

eating herbs

The Structure of Populations

Boundaries of the Geographic Range

Plants adaptions to biotic

and abiotic factors

determine the geographic range

limiting factor

determines health of the plant

Cross-link Description: Light can be a limiting factor and is very important for the plants health. This can be why plants compete for light by shading over other plants.

determined by environment

any factor of an ecosystem

examples

amount of sunlight

amount of water

amount of herbivores in area

dependence on animals for

pollination

seed dispersal

Local Geographic Distribution

3 types

Random Distribution

no obvious, evident pattern

no predictive value

seems to be most common

Clumped Distribution

spacing between plants is either

small

large

reasons

seeds fall

certain distance from plant

fruit eaten by animals

will deposit seeds

within certain area

Uniform Distribution

Examples

orchards

tree plantations

individuals evenly spaced

not common in

natural habitats

r- and K-selection

r-Selection

r conditions

produced by disturbance

flood

fire

good for

surviving individuals

seeds arriving via floods/winds

most find best habitats

r-selected species

typically

annuals

small shrubby perennials

at disadvantage when

habitat goes back to normal

killing temperatures

Cross-link Description: The plants that inhabit a soil after a disturbance are known as the pioneers. They are known to create better soil. But may be at a disadvantage when conditions become better.

K-Selection

Conditions

in a crowded habitat

population close to carrying capacity

K-selected species

select differing phenotypes

than those that are beneficial

in a disturbed habitat

Energy mostly goes to

antipredator defenses

Examples

redwoods

results in

slower

growth

reproduction

Douglas firs

bristle-cone pines

The Structure of Ecosystems

Physiognomic Structure

physical size and shape

of

the organisms

organisms distribution

in relation to

each other

physical environment

Life Forms

Therophytes

Geophytes

Hemicryptophytes

Chamaephytes

Phanerophytes

Underground buds

buds located above ground

annual life span

buds located at surface

buds located high above

Temporal Structure

changes that an ecosystem

undergoes with time

days

seasons

decades

Species Composition

refers to the

number and diversity

of species in

an ecosystem

depends on

climate type

soil quality

species tolerance range

Trophic Levels

basically feeding levels

primary producers

autotrophs

first step of food web

energy supplier for

Primary Consumers

prey on by

Secondary Consumers

Decomposers

break down

Cross-link Description: Species composition could be relatively low after a phenomena because the soil and climate would have changed. Thus the species adapted to the previous ecosystem could be in danger.

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