Chapter 14
14-1
•A habitat differs from a niche.
A habitat is all aspects of the area in which an organism lives.
•Biotic factors – all living organisms within an ecosystem (ex. Birds, trees,
bacteria)
•Abiotic factors – physical or non-living factors (ex. Climate, temperature,
precipitation, wind sunlight, soil)
•Together, biotic and abiotic factors determine the survival and growth of an
organism and the productivity of the ecosystem in which the organism lives.
•What biotic factor affects the size of a population? Number and kinds of
predators in the ecosystem.
•Example of a change in an abiotic factor: No rain – mountain lion leaves his
area to find water somewhere else.
•Resource availability gives structure to a community.
Species can share habitats and resources.
A niche is the full range of physical and biological conditions in which an organism
lives and the way in which the organism uses those conditions. For example, food,
physical conditions, reproduction (when and how)….
•Can also be known as the role and position that a certain species of animal
occupies.
•A fundamental rule in ecology, the competitive exclusion principle, states
that no 2 species can occupy the same niche in the same habitat at the same
time. Competitive exclusion keeps two species from occupying the same
niche.
•The area where an organism lives that includes biotic and abiotic factors is
called its habitat. Two species can share the same habitat, but not the same
niche.
•Ecological equivalents are species that occupy similar niches but live in
different geographical regions.
14-2
•Competition and predation are two important ways in which organisms
interact. Community interactions, such as competition, predation, and various
forms of symbiosis, can powerfully affect an ecosystem.
•Resource refers to any necessity of life, such as water, food, etc…
•Competition occurs when two organisms fight for the same limited resource.
–Intraspecific competition
–Interspecific competition
–Predation occurs when one organism captures and eats another. (predator –
kills and eats; prey – food source)
Any relationship in which 2 species live closely together is called symbiosis.
•There are three major types of symbiotic relationships.
Parasitism: one organism benefits, the other is harmed. Parasites meet their
needs as ectoparasites (such as leeches) and endoparasites (such as
hookworms)
Mutualism - both species benefit from the relationship (flower and insects)
Commensalism - one benefits and the other is neither helped, nor harmed.
(barnacles on whales)
14-3
•Population density is the number of individuals that live in a defined area.
Scientists can calculate population density. Population density is the number of
individuals per unit area ex. 100/km2
Geographic dispersion of a population shows how individuals in a population
are spaced.
•Population dispersion refers to how a population is spread in an area.
•There are three types of dispersion: clumped, uniform, random.
•Survivorship curves help to describe the reproductive strategy of a species.
•A survivorship curve is a diagram showing the number of surviving members over
time from a measured set of births.
•Survivorship curves can be type I, II or III.
14-4
•Changes in a population’s size are determined by immigration, births,
emigration, and deaths.
•The size of a population is always changing.
** A population will increase or decrease in size depending on how many individuals
are added to or removed from the population.** ex. Many births increase
population; a natural disaster such as a hurricane will decrease it.
A population can grow when its birthrate is greater than its death rate. Birthrate
equals death rate, population stays the same. Death rate greater than birthrate,
population decreases.
Immigration – movement of individuals into an area (population increase).
Emigration – movement of individuals out of a population (population decrease).
•Population growth is based on available resources.
Exponential growth is a rapid population increase due to an abundance of
resources. Under ideal conditions, with unlimited resources, a population will grow
exponentially
Logistic growth is due to a population facing limited resources. As resources
become less available, the growth of a population slows or stops.
Carrying capacity is the maximum number of individuals in a population that the
environment can support.
•Ecological factors limit population growth.
•A limiting factor is something that keeps the size of a population down.
Density-dependent limiting factors are affected by the number of individuals in a
given area. Density dependent factors become limiting only when the population
density reaches a certain level. Density dependent limiting factors include:
•Competition – when populations become crowded, organisms compete or struggle
for food, water, space, and other essentials for life.
*the more organisms in an area, the sooner the resources will be used up
•Predation – the populations of predator and prey go up and down
*prey population increases, predator population increases; prey population
decreases, predator population decreases; cycle starts again
•Parasitism - parasites take nourishment from host causing weakness or death,
affecting population numbers.
•Disease
Density-independent limiting factors limit a population’s growth regardless of the
density. Density-independent factors affect all populations in similar ways
Examples: 1) unusual weather
population 2) natural disasters
crashes
3) seasonal changes
then
4) damming rivers
rebuilds
5) cutting timber
14-5
Ecological Succession occurs following a disturbance in an ecosystem
o This series of predictable changes that occur in a community over time is
called ecological succession.
o 3 ways that ecological succession can happen (physical changes)
1. slow physical changes over time (ex. Trees growing large)
2. sudden natural or human disturbance (ex. Clearing a forest for land
development)
3. natural disaster (ex. Hurricane, tornado, eruption)
o Primary Succession is when succession occurs on land surfaces where no
soil exists, for example, rock, volcanoes….
o The 1st species to populate the area are called pioneer species. Lichens
are a pioneer species. They are made up of a fungus and an alga and can
grow on bare rocks. As they grow, they break up rocks. When they die, they
add organic material to help form soil in which other plants can grow.
o Secondary Succession occurs when a disturbance of some kind changes
an existing community without removing the soil. (land cleared and plowed
for farming and abandoned, wildfires) *Final stage of succession for a pond
would be to fill with soil.
o Factors that influence continual change: long-term climate changes, further
disturbances, introduction of non-native species.
o Natural disturbances interrupt succession.