What effect can environmental selection pressures have on species in an ecosystem?
Changes in toads due to selection pressures
Impact of cane toads on other species
Ecosystem: savanna woodlands, Kakadu National Park
Ecological niche
Cane toads
introduce to Australia 1935
quickly spread from release sight
have a unique combination of structural and behavioural features
enabling them to thrive
feed at night
ground dwellers
eat a wide variety of opportunistic foods
absorb water through skin
can breed all yr round
females lay up to 30000 eggs and hatches in 2-3 days
role an organism plays in community
relationship between
populations of species
Abiotic and biotic factors
each organisms has unique niche
due to different set of adaptations
do not compete for same resources
able to coexist
each species responds differently to resources & competitors, until occupy own niche
2 hypotheses explaining cane toad invasion success
environmental selection pressure
invasive
empty niche hypothesis
competitive niche hypothesis
invaders occupy vacant niche space in community
cane toads have distinct traits #
unique morphology from aus frogs
invaders overlap with native species in niche space
same function
same resources
same competitors
same habitat
however thrives better in environment #
displaces native species
due to no native predators & unique traits
community of living organisms and their physical environment which they interact with
abiotic factors that affect cane toads
biotic factors that affect cane toads
climate
sunlight
soil
water
monsoonal
tropic climate
lots of rainfall
very wet and dry seasons
affects toads as they can dessicate
important for plant growth
important for 1st order consumers
what toads eat
during wet seasons lots of nutrients
good for plant growth #
essential for all organsisms
major source of water in savanna woodlands
need water to keep moist & reporduce
animals
plants #
predators
prey
competitors
autotrophs
vital part of food chain
make up habitat
birds
reptiles
mammals
amphibians
insect-eating birds
lizards
rapid decline in populations
acts as a selection pressure
doesn't affect all members of population
variation
some more tolerant to poison
some are vulnerable to poison
preference to eat cane toad
on red bellied black snake
on northern quoll
gate limited predators
strong negative allometry for head size
head size as lower growth rate than body size
can't consume predators prey bigger than mouth size
cane toad- selection pressure on head size
small head
big body
smaller mouth
less dose of toxin throughout body
not big enough to eat large toads
favours individuals with small heads and big bodies
small toads
not fatal
drastic population decrease when toad arrived
populations in QLD stopped eating cane toads
genetic and/or behavioural reason
reproductive advantage over quolls with this gene
gene that makes quolls 'toad adverse'
taste aversion learning
genetic diversity among individuals #
led to survival & adaptation
minimise niche overlap
cane toad decreases population of preys and predators
population of organisms they eat will increase
affect pre-existing food chains
fast reproduction rates
lack of natural predator
advantage
competitive exclusion
drive evolutionary change
promotes reproduction rates
evolved
behavioural adaptation
structural adaptation
fast hopping style
straight hoppers
larger, longer legs
hides in moist crevices
moves is straight lines
inflates lungs to appear bigger
used to move 10km/yr
now move 40-60km/yr
loss of habitat of other species
rainbow bee-eater's
cane toad destroys burrow
large goannas
decrease in population leads to increase in population of what they eat
insects, birds, small mammals, reptiles
as toads spread across, spatial sorting
faster toads at front
genetic trait is passed down
get more food, have more babies
more athletic
invasion and flat terrain favour toads that travel quickly
natural selection for speed
