Download Section 1.1 Silence of the Frogs

Biodiversity Case Study
THE SILENCE OF THE FROGS
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Biodiversity Case Study
THROUGH THIS CASE STUDY ON FROGS
WE WILL LEARN ABOUT:
-
BIODIVERSITY LOSS
FOOD CHAINS
FOOD WEBS
Disappearing Frogs
Problem
 Frogs have survived multiple
extinctions over the last 250
million years of Earth’s history.
 They can be found in most
ecosystems that contain water
Disappearing Frogs
Problem
 Scientists are noticing a decline in frog populations and the # of species
of frogs.
 Over 30% of North American frog species are in trouble!
Question
Why are scientists concerned about frogs?
Disappearing Frogs
Answer
Scientists believe that frogs are a
good indicator species.
Indicator Species: a species
with a population that varies
with the health of an ecosystem.
Why are Frogs an Indicator Species?
Frogs are considered top be indicator species because they live two
different lives!
Why are Frogs an Indicator Species?
Life #1: In aquatic ecosystems as eggs and tadpoles.
Life #2: In terrestrial/aquatic ecosystems as adult frogs.
Tadpoles
Frogs
Why are Frogs an Indicator Species?
By studying frogs we can find evidence for problems in both aquatic and
terrestrial ecosystems.
Ponds
Forests and Grasslands
African Bullfrog
 Video 1
 Bullfrog battle
Frogs and the Food Chain
 Because they exist in two ecosystems,
frogs are a part of two very different food
chains
Food Chain: a step-by-step sequence
showing a feeding relationship in an
ecosystem.
Mr. T must be at the top
of the food chain
Frogs and the Food Chain
As an Herbivore (Pond Ecosystem)
Algae
Producer
Tadpole
Consumer
(Herbivore)
Water Boatman
Consumer
(Carnivore)
Trout
Consumer
(Carnivore)
Frogs and the Food Chain
As a Carnivore (Forest Ecosystem)
Grass
Producer
Grasshopper
Adult Frog
Consumer
(Herbivore)
Consumer
(Carnivore)
Heron
Consumer
(Carnivore)
Disappearing Frogs
 What effect would the loss of frogs have on an ecosystem?
Consider the food chain / web!
No Frogs = More Insects!
=
 More insects like Mosquitos means
problems for humans
 Mosquitos carry malaria, a life
threatening parasitic disease.
 Cases of malaria have increased in
areas where frog populations have
declined.
Disappearing Frogs
 How does this affect OTHER species in the same ecosystem??
=
Disappearing Frogs
Ecosystems do not only operate in simple food chains! Food webs
represent more complicated feeding relationships in ecosystems
There are other things that feed off the same insects as frogs. They would
have more food once frogs are gone.
So Why are Frogs Disappearing?
 Scientists have identified four main reasons:
1) Habitat Destruction
2) Pollution of Air and Water
3) Ultraviolet Radiation
4) Climate Change
All of these factors are enhanced or directly caused by human activity.
Why are Frogs Disappearing??
1) Loss of Habitat (place to
live)
 Frogs need ponds and
wetlands, to lay eggs and
keep their skin moist.
 As adults they need forests
and grasslands to catch
insects.
Why are Frogs Disappearing??
1) Habitat Destruction
 Forestry
 Farming
 road construction
 growth of towns and cities
These all destroy frog habitat!
Habitat: where an organism lives
Why are Frogs Disappearing??
2) Pollution of air and
water
 Water pollution
 Frogs
have lungs but also
breathe through their skin!!
 Their skin is THIN and
pollutants can pass through!
Close up of frog skin!
Why are Frogs Disappearing??
2) Air and water quality
 Acid Rain
 Water becomes more acidic
 This causes reproductive and
growth problems
 Fewer
Eggs fertilized
 Embryos develop more slowly
 Deformed tadpole limbs!
Why are Frogs Disappearing??
3) Ultraviolet Radiation
 Frogs thin skin is sensitive to UV
radiation from the sun
 Depleted ozone layer means more
radiation gets to earth
 Damages frogs skin
Harms humans too! More
skin cancer!
Why are Frogs Disappearing??
4) Climate Change
 People burn fossil fuels
that contribute to global
warming.
If it gets drier = less habitat
for frogs
Why are Frogs Disappearing??
4) Climate Change
If it gets wetter = faster
rivers and less insects so
less food
If it gets wetter = faster
rivers and less insects so
less food
Habitat Destruction