Download Population Ecology - Effingham County Schools

Population Ecology
Dynamics of Ecosystems
I. Ecological Hierarchy
Individual
Population
Community
Ecosystem
Biome
Biosphere
II. Population: same species living in an area
} Species = group of similar organisms that can
interbreed
} Example: all the Giant pandas in a forest
III. Community: group of different populations
living in same area
} Example: All the different plants & animals in a
forest with the panda
}  Definitions
} Population Ecology: major sub-field of
ecology that deals with dynamics of
species populations & how these pops
interact with the environment
} Population Dynamics: studies short- and
long-term changes in size, density & age
distribution of pops, and the biological
and environmental processes influencing
those changes
¨ Birth and death rates
¨ Immigration and emigration
¨ Pop decline
•  Population Distribution aka Dispersion:
Clumped– helps w/ protection Uniform – helps reduce intraspecific Random – seen in some plants •  Population Size
o  Changes with 4 variables:
1. Births
2. Deaths
3. Immigration
4. Emigration
•  Pop change = (Birth + Immigration) – (Death + Emigration)
•  Age structure also influences pop change
o  = Numbers of prereproductive, reproductive, &
postreproductive individuals
•  Biotic potential = Populations vary in their capacity for
growth
o  Intrinsic rate of increase (r) = rate of pop growth w/ unlimited resources
•  A pop with few resource limitations will grow exponentially
(J-shaped curve):
o  *Humans
}  Most pops grow < intrinsic rate of increase (r) b/
c of environmental resistance
}  Environmental resistance: all factors that act to limit
pop growth
}  Can be Abiotic or Biotic
}  Can be Density-independent
or Density-dependent
https://www.youtube.com/watch?v=QI2ixJeIxEU
Serious Science Biological Carrying Capacity
}  Density-independent factors
= Any factor in the environment that
does not depend on the number of
members in a population per unit area
Weather events
Fire
Human alterations of the landscape
Air, land, and water pollution
}  Density-Dependent Factors
Any factor in the environment that
depends on the number of members in a
population per unit area
Predation
Disease
Competition
Parasites
•  Biotic Potential
vs.
Environmental
Resistance
o  Generally come to
some equilibrium:
•  Carrying Capacity (K)
•  = max number of individuals of a given species that can
be sustained indefinitely in a given space
o = equilibrium b/w biotic potential and environmental
resistance
•  Populations w/ a carrying capacity show logistic growth (Sshaped curve):
o  Start off with rapid exponential growth
o  Followed by a steady decrease at K
•  Logistic Population Growth:
}  Some organisms overshoot carrying capacity à
results in a pop crash (dieback)
}  Due to reproductive time lag (period needed for birth rate to fall & death
rate to rise in response to resource overconsumption)
Tasmanian Sheep
Alaskan Reindeer
•  There are 4 Types of Population Change Curves
}  4 Types of Population Change Curves
1.  Stable: stay generally around K
} 
Seen in consistent environments like tropical rain forests
2.  Irruptive: stay stable except for occasional peaks &
crashes
} 
Seen in insects & algae (in temperate climates); raccoon &
house mice
3.  Cyclic: regular fluctuations
} 
Seen in lemmings; lynx & hare
4.  Irregular: no pattern
•  Predator & Prey Population Cycles
o  Pop cycles of predator influence pop cycles of prey & visa-versa
o  Examples: Lynx & Hare; Wolf & Moose** (**worksheet)
•  Sexual Strategies & Patterns:
•  Asexual reproduction: does not require sex cells
(gametes). Aka Mitosis – cloning.
o Bacteria reproduce this way. Only 3% of all species use
this form
•  Sexual reproduction: requires gametes à results in
genetic recombination
Disadvantages
Advantages
½ pop doesn’t give birth
Increased chance of genetic defect/error
Courtship and mating rituals can be
complex
Genetic variety/diversity!!
Parents can divide responsibilities
•  Sexual Strategies & Patterns:
o  Reproductive Patterns: 2 types
•  Classification of species’ reproductive pattern depends
on their position on the population growth s-curve
o r-selected species
o K-selected species
https://www.youtube.com/watch?v=Bu6ouKt9zhs
Bozeman Science
•  r- selected species/ Opportunists
o  Capacity for high rate of pop increase
o  Reproduce early
o  Many, small offspring
•  Most don’t survive
o  No/ little parental care
o  Generalist niche
o  Examples:
•  Algae
•  Bacteria
•  Rodents
•  Insects
•  Annual plants
•  K-selected species/ Competitor
Show lower pop growth rate
Reproduce late in life
Few, larger offspring
More parental care
Specialist niche
Do well in competitive situations, with stable
env conditions
o  *Prone to extinction
o  Examples:
•  Large mammals
•  Birds of prey
•  Large, long-lived plants
o 
o 
o 
o 
o 
o 
•  Different reproductive strategies have different types of
survivorship:
o  = percent of individuals surviving to certain ages
•  3 Types of Survivorship Curves:
•  3 Survivorship Curves:
•  Type I: Late Loss
o  Low infant mortality & long life spans
o  Tend to be K-selected species
o  Examples: humans (in developed countries); large mammals
(elephants, big cats, etc.)
•  Type II: Constant Loss
o  Death rate even among all ages
o  Examples: some birds, some invertebrates, rodents
•  Type III: Early Loss
o  High infant mortality and then constant mortality for few remaining
o  Seen in most r-selected species
o  Examples: annual plants, small fish, marine invertebrates, insects
Community Ecology
How do organisms interact?
Community Ecology
•  Community Structure is based on:
1.  Physical Appearance: size & distribution of its
populations
2.  Species Diversity: combination of
o Species richness: # of different species
o Species evenness: abundance of individuals within each
species
3.  Niche structure: # of niches and species interactions
•  Species Equilibrium Model (E.O. Wilson)
•  aka Theory of Island Biogeography
o Balance b/w 2 variables determines
the number of different species found on
an “island”:
•  rate at which new species immigrate to the island
•  rate at which existing species become extinct on the island
•  3 factors must be taken into account:
1. Immigration and extinction rates
2. Island size
3. Distance from “mainland”
Useful when protecting wildlife on “habitat Islands”
a.k.a areas surrounded by development
Remember the Major Roles
that Species Can Play within
Ecosystems cont.:
1. 
2. 
3. 
4. 
5. 
Native
Nonnative (Invasive)
Indicator
Keystone
Foundation species
SE Asia Durian Fruit & Bats (a.k.a Flying Foxes)
Mutualism (+, +)
Endangered due to
1.  hunting for their meat
2.  Deforestation
3.  Targeted to keep them from eating
commercially grown fruit
Keystone
1.  sustains tropical community
2.  pollinates many plant species
3.  disperses seeds in droppings &
therefore maintains forest biodiversity
https://www.youtube.com/watch?v=69IGcIp-AZg
•  Invasive Species
•  1957 Brazil imported African
Bees for honey production,
instead they displaced
domestic bees and reduced
honey supply
•  They have since moved north
& reached the United States
•  They are aggressive &
unpredictable, kill 1000’s of
domesticated livestock and
about 1000 people due to
allergies
•  So far winter stops them from
spreading
farther north
https://www.youtube.com/watch?v=y7C--Cv4gPw
Indicator Species
Species
What do they Indicate?
Trout
Water Quality; require clean water w/high D.O. Birds & BuAerflies
Chemicals & habitat loss; found everywhere
Amphibians (frogs, salamanders, & toads
Pollutants in air, water, & soil, UV light, habitat loss (filling in wetlands), drought, overharvesting;
Live in water as herbivores & as adults on land as carnivores, thin permeable skin, eggs have no protection, https://www.youtube.com/watch?v=BvidpapF1bg
Sci Show
https://www.youtube.com/watch?v=1q5oe33M15Q
Scary Bat Die off
http://www.smithsonianmag.com/videos/category/wildlife/saving-amphibians-from-deadlyfungus/
Amphibian Chytrid Fungus
Keystone & Foundation Species:
American Alligator
hunted for meat, skin, and/or for
sport
1950-1960 90% decline in LA
1967 put on endangered species
list
1977-1987 upgraded to
threatened list in 8 states
Keeps areas free of vegetation,
digs deep depressions that fill
with water & serve as refuge for
aquatic life, feed on predatory
gar
https://www.youtube.com/watch?v=_IWw8Ruz8Uo
Keystone Species and their Role 3:59
https://www.youtube.com/watch?v=0-PE3ve3w2w
Bozeman Science 7:35
Species Interactions:
Competition= occurs between two species for resources (food,
space, etc.)
Gause’s principle states that no 2 species can occupy same niche at
same time à 1 species must relocate, die out or change niche
Over a time scale long enough for natural selection,
Resource Partitioning can occur:
Species minimize competition by
filling specific niches within an
ecosystem (traits allow them to utilize
resources at different times, locations or ways)
Ex: North American warblers hunt for
insects in same spruce trees, but at
different parts & times
Symbiotic Relationships An interactive
association between two or more species
living together
Predation (+, -)
Interaction b/w organisms in which one
organism (predator) captures and feeds
upon another (prey)
Preys’ Defense Mechanisms:
Physical adaptations: highly
developed sight & smell; shells;
spines; thorns; Camouflage & mimicry
Chemicals: poisons, irritants, odors,
ink clouds
Behaviors: puffing up, mimicking a
predator, playing dead
Cuttlefish
Hognose snake
Praying mantis
Parasitism: when one organism (parasite) feeds on or otherwise
harms another organism (host) in close association (+,-)
Different from predation in that parasite is generally smaller than host and
doesn’t kill host, but harms over time
Tick (Ectoparasites)
Mistletoe
Brood parasitism
Video: https://www.youtube.com/watch?v=XuKjBIBBAL8
David Attenborough Parasites
Commensalism: benefits one species but has little or no
effect on other species (+, 0)
Whales & Barnacles
Epiphytes (Bromeliads &
some Orchids)& Trees
Mutualism: interaction benefitting
both species (+, +)
Pollination Mutualism
Nutritional Mutualism:
Lichen (fungi & algae)
Gut Inhabitant Mutualism
All communities change their structure & composition over time in
response to each other & changing environmental conditions
Disturbances: change in environmental conditions that disrupts a
community or ecosystem. These disturbances can range from mild to
catastrophic and can be caused by natural occurrences or human
activities:
Ecological Succession = gradual change in species composition
Two Types:
•  Primary Succession
•  Secondary Succession
•  Primary Succession: the gradual establishment of
biotic communities on lifeless ground (rock)
Pioneer
Species start
soil formation
process: trap
soil particles &
detritus in
wind, secrete
acids to break
down rock
Pioneer
Species
(Lichens,
Algae,
Bacteria,
Moss)
Late
successional
species
Mid
successional
species
End in Mature
Community
(long-lived
hardwoods)
•  Secondary Succession: when biotic communities are
established in an area where some type of biotic
community is already present
•  Occurs after disturbance (burned forest, polluted stream,
abandoned farmland)
•  Intermediate Disturbance Hypothesis: communities
that experience fairly frequent but moderate
disturbances have the greatest species diversity
Succession Model Online
•  http://www.mrphome.net/mrp/succession.swf
•  Measuring Biodiversity
o Shannon’s Diversity Index (H): range from 0 to 5
(more diverse)
o Simpson Diversity Index (D): range from 0 (zero
diversity) to 1 (infinite diversity)
•  Shannon’s Diversity Index
s
H = -∑ (Pi * ln Pi)
i=1
H = the Shannon Diversity index
Pi = fraction of the entire population made up of species i
(ni/total)
S = numbers of species encountered
∑ = sum from species 1 to species S
•  Simpson Diversity Index
s
D = 1 -∑ [(ni / N) 2]
i=1
D = the Simpson Diversity index
ni = number of individual per species
N = total number of individuals
S = numbers of species encountered
∑ = sum from species 1 to species S
•  Shannon’s Diversity Index
Birds
Pigeon
Robin
Starling
Crow
House Sparrow
Ni
96
1
1
1
1
Pi
.96
.01
.01
.01
.01
ln Pi
-.041
-4.61
-4.61
-4.61
-4.61
- (Pi * ln Pi)
.039
.046
.046
.046
H = 0.223
.046
•  High values of H would be representative of more diverse communities.
•  If the species are evenly distributed then the H value would also be high.
So the H value allows us to know not only the number of species but how
the abundance of the species is distributed among all the species in the
community.