Biodiversity,
Species Interactions, and
Population Control
Chapter 5
1
Where we’ve been…

Chapter 3
◦ Looked at ecosystem components and how energy cycles
within ecosystems

Chapter 4
◦ Defined biodiversity. Looked at factors affecting
biodiversity and how it is measured.
Where we are headed…

Chapter 5
◦ Look at how species interact with each other and how
ecosystems respond to changes in environmental
conditions.
Species Interactions

Five Major Ways that Species Interact with one
another:
◦ 1. Interspecific Competition
◦ 2. Predation
◦ Symbiosis (two species living closely together)
 3. Parasitism
 4. Mutualism
 5. Commensalism
Interspecific Competition

When two or more species interact to gain access to the
same limited resources (food, water, light, space)
◦ Intraspecific: same species competing for resources
◦ Resource partitioning: species evolve traits to minimize
competition with other species
◦ As our footprint grows larger, we are impacting species even
more (habitat loss)
 Humans competing with other species for space and access to
resources
Predation

When one member of a species feeds on a
member of another species
◦ Predator-prey relationship
◦ Predators and prey often co-evolve traits that either allow
them to find prey or hide from predators better
◦ Predators play important roles in ecosystems (help to
keep other species in balance)
Symbiotic Relationships--Parasitism

When one organism lives on or inside of another
organism
◦ Parasite benefits, host organism harmed (not immediately
killed)
 Parasite dies if host killed
Symbiotic Relationships--Mutualism

Interaction that benefits both species
◦ Unintentional exploitation of the other organism (not
cooperation)
Symbiotic Relationships-Commensalism

Interaction that benefits one species and has little
or no effect the other
Population Dynamics

Population: group of interbreeding individuals of the same
species
◦ Most organisms live together in clumps

Changes in population size influenced by:
◦ Births and deaths
◦ Immigration and emigration
◦ Population change= (births + deaths) – (immigration + emigration)
◦ Age structure diagrams can also be used to describe
organism populations
◦ -identify if population is growing, stable or declining
Limiting Factors

Populations have a range of tolerance. A set of physical
and chemical conditions that they will thrive under.
◦ Small variations in a population will exist due to genetic
differences
◦ “optimal range of tolerance”—conditions in which most
organisms survive
◦ Limiting factor principle: too much or too little of any physical or
chemical factor can limit or prevent growth of a population
◦ Examples of limiting factors?
Range of Tolerance

Carrying capacity: maximum number of individuals
an ecosystem can support.
◦ Environmental resistance: combination of all limiting
factors determines carrying capacity
◦ Exceeding carrying capacity causes population to crash
 Overshoot and die off

Population density: number of individuals found in
a particular area
◦ Density dependent limiting factors
 Parasitism, infectious disease, competition
◦ Density independent limiting factors
 Weather events, fire, pollution, habitat destruction
Reproductive Strategies and
Survivorship

R-strategist (type 1)

K-strategist (type 3)

When graphed these two reproductive strategies produce
unique survivorship curves
◦ Many small offspring with little or no parental care
◦ Large losses of young offspring, so produce large numbers to
compensate
◦ Examples: algae, bacteria, insects, some fish species
◦ Reproduce later in life, few offspring
◦ Longer lifespan, mature slowly with parental care
◦ Examples: mammals, birds
◦ Classified as type 1, 2 or 3 depending on mortality rates



Type 1: low infant mortality and high survival
Type 2: constant decline
Type 3: high infant mortality few reach adult
Population Calculations

Annual Growth Rate
◦ (CBR-CDR)/ 10 = % growth
** Does not include immigration or emigration

Change in Population per year

Population Density
◦ Population change= (births + deaths) – (immigration + emigration)
(Number of individuals)
/ (area sampled)

Doubling Time

Birth and Death Rates
(births or deaths per year) / (Total Population)
**Crude birth and death rate multiply by 1000
◦ 70/ annual growth rate = doubling time of a population
16
Response to Ecosystem Change

Ecological Succession: gradual change in species
composition in an ecosystem after a significant
disruption
◦ Primary succession: gradual establishment of living
organisms in lifeless areas where there is no soil or
sediment (aquatic)
 bare rock, parking lots, new ponds or reservoirs, cooled lava
 takes a very long time
◦ Secondary succession: series of communities and
ecosystems develop in places containing soil or sediment
 abandoned farmland, burned/logged forests, polluted
streams, flooded land
 can relatively happen quickly
17
18

Succession increases species richness and complexity
of food webs

enhances energy flow and nutrient cycling which
promotes increased biodiversity

does follow an unpredictable path

resilience of ecosystems: ability through succession to
rebound to previous state after significant disturbance
◦ rainforests highly complex and diverse, very difficult to return to
previous state
 “Ecological tipping point”—ecosystems won’t recover when past this
point
19
Succession and Mt. St. Helens

May 18, 1980
erupted violently

Deadliest and most
destructive volcanic
eruption in US
history

Eruption reduced
the height of the
mountain by 1300
feet
20

The Mt. St.
Helens
National
Volcanic
Monument
was created to
preserve the
volcano as
well as
provide the
land for
scientific
study.
21
22
Article Reading and Questions

Read the article: Mt. St. Helens 30 Years Later

Answer the following questions.
◦ Describe the impact of the MSH eruption on the
surrounding ecosystem. Give specific details.
◦ Describe how succession is reshaping the MSH
ecosystem. What has been observed in the past 30+
years?
◦ What are the concerns with the MSH ecosystem looking
toward the future?
23