Chapter 14
Interactions in an Ecosystem
Animals and Their Habitats
Biotic vs. Abiotic Factors
• An ecosystem is made of both biotic and
abiotic factors.
• What biotic factors might scientists find in a
Spectacled Bear’s habitat?
• What abiotic factors might be in a Spectacled
Bear’s habitat?
• How do these factors differ for Polar Bears?
Habitat vs. Niche
• Habitat – describes the organism’s
environment
• Niche – describes how the organism interacts
with its environment
– Includes both biological and physical conditions in
which an organism lives and how the organism
uses those conditions for survival
– It can include its place in the food web, preferred
temperature, and abiotic factors
– It is specific to each organism
Competitive Exclusion Principle
• This fundamental rule of Ecology states that
no two species can occupy the same niche in
the same habitat at the same time
• Why?
Symbiosis
• Symbiosis – any relationship where two
species live in close contact
• Mutualism – both species benefit from the
relationship
• Commensalism – one species benefits and the
other is neither helped nor harmed
• Parasitism – one species harms the other
Mutualism, Commensalism or
Parasitism?
How Populations Grow
• Important characteristics of populations:
geographic distribution, density, growth rate
• Population density – number of individuals
per unit area
• Population dispersion patterns: clumped,
uniform and random
Survivorship Curves
• Survivorship curves are generalized diagrams
showing the number of surviving members
over time from a measured set of births.
• Type 1 – large mammals, low infant
mortality, large number of elderly
• Type 2 – birds, small mammals, reptiles,
equal survivorship rate through out
ages
• Type 3 – fish, amphibians, plants, high
mortality, high birth rates
Population Growth
• Populations fluctuate depending on different
ecological pressures: births, deaths,
immigration, emigration, etc.
• Immigration – individuals moving into an area
• Emigration – individuals moving out of an area
Exponential Growth
• Occurs when the individuals in a population
reproduce at a constant rate
• Typically occurs when a population has
abundant space and food, and is protected
from predators and disease
• Characterized as “unrestricted growth”
meaning there are no external pressures
placed on the population
• Will cease when carrying capacity is reached
Logistic Growth
• Begins as exponential growth
• Population growth slows as a population
reaches its carrying capacity – the largest
number of individuals an environment can
support
• Birth rate may decline, death rate may
increase, immigration or emigration may be
fluctuating
Limits to Growth
• Limiting Factor – a factor that causes
population growth to decrease
• Examples:
Density-dependent Limiting Factors
• These factors depend on population size
• Competition – what happens when the
population increases, but resources stay the
same?
• Predation – natural way of controlling population;
predator-prey relationship is fluctuating
• Parasitism and Disease – may become more
prevalent during high population density; limits
population size similarly to predation
Density-independent Factors
• Affects all populations in similar ways,
regardless of population size
• Examples:
Ecological Succession
• Ecosystems change in response to human as
well as natural disturbances.
• What happens to an area after a forest fire?
After a volcanic eruption?
• Primary succession – succession the occurs
where no soil exists and usually begins with
pioneer species
• Secondary succession – when change to the
land occurs without removing the soil
Human Population Growth
• Human populations are affected by the same
type of factors as other populations
• Because of technology, we have been able to
increase our population size quickly
• Some say we have reached or even exceeded
Earth’s carrying-capacity
• At the moment, we are still experiencing
exponential growth
• Do you think we will experience logistic growth at
some point?
Patterns of Population Growth
• Demography – the study of human
populations
• Scientists try to predict how human
populations will change over time based on
birth rates, death rates and age structures
• Population growth has slowed in the US,
Japan and Europe in the last 100 years
• Scientists refer to this as the demographic
transition
Age Structure Diagrams
• Can be used to predict future population
growth