lecture 5 ecology Flashcards
communtiy dynamics the three components
function, structure, dynamics
function – community
– species interactions (predation, competition)
– energy and nutrient flow
structure – community
– species richness (number of species)
– composition (relative abundance of species)
what does relative abundance of species mean
do you have an equal distribution, or species that are rare and some that are not
dynamics community
change in structure or function over time
trophic interactioons
interactions related to feeding, – predation, herbivory, paratisism
what do food webs represent
trophic interactions
trophic level – what is it
verticle position in the food web
what do the arrows in a food web represent
direction of energy flow
what are primary producers typically relative to food web and trophic level
trophic level one – as you go up in consumers, trophic level increases one by one
Tundra food web characteristics
mostly short food chains – lemmings graze on almost all of primary producers, and are eaten by most predators – they are important connector to the food web
species with large impact
dominant species, ecosystem engineers, keystone species
dominant species
high biomass/abundance, can feed on a variety of species – large impact due to high biomass
ecosystem engineers
large impact because they alter physical environments – think beavers and dams and how they affect water flow by building their dams
keystone sp[ecies
not a lot of them – relatively low in abundance – large impact despite how low biomass and abundance, usually predators
reason why predators are important
top down control
what is top down control
higher trophic level reduces abundance or biomass of lower trophic level.
- primary producers –> herbivores (direction of energy flow)
herbivores –> primary producers (direction of impact)
herbivores graze grass, increase in herbivores, decrease in grass
trophic cascadxe
cascading down trophic levels – indirect – impact of top predators extends to lower trophic levels
primary producer –> herbivore –> predators (energy flow direction)
predators –> herbivores –> primary producers (direction of impact)
the predators prey on herbivores, decreasing their abundance, and because of this decrease in herbivores the primary producers recover and increase in abundance.
pacific coast, sea otters, british columbia 1960
1960 – no sea otters
top-down control – sea urchins were abundant, they cleared out all kelp.
british columbia 1970
sea otters return, top down control between otters and urchins, – urchins reduced because of food source of otters
british columbia 1970 putting it all together
because sea otters reduced abundance of urchins, kelp was able to rewcover and grow forests. (trophic cascade)
what is a sea otter an example of
keystone species – impact on community
– 1. fewer herbivores (sea urchins, starfish)
– 2. more kelp – more productive, physical structure , provided habitat for fish therefore richness increase
Alaska 1990s
due to overfishing, Ocras diet switched and it preyed on otters. reduction of otters meant increase in urchins which meant decrease in kelp
Atlantic coast –historical top down
large predatory fish – hunted sea urchins – increased kelp
then overfishing caused increase in urchins and decrease in kelp
why is there a fluctuation on the atlantic coast
urchin disease – depends on temperatyure, warmer it is, pathogens can entewr ecosystem and affect urchins.
regime shift
abrupt shift to a very different and persistent community
what causes regime shifts
usually external drivers – removeal of keystone species, arrival of disease, climate change, nutrient inputs
top down vs bottom up controm
top down
– higher trophic level controls abundance or biomass of lower trophic level (herbivores limit primary producer biomass)
dottom up
lower trophic level controls abundance or biomass of higher trophic level (primary producers limit herbivore biomass)(food limited)`
top dowqn critical points
- Top predators frequently exert top down control
- without predators, heerbivores often have strong impacts on primary producers.
applications to top down control
– wildlife managment in absence of top predators (reintroductions to re establish ecosystem)
– management of insect pests
– management of natural resources (limits to fishing)
zoonotic disease
disease transferred from animals to humans
what is lyme disease
caused by a spirochaete (bacteria) – pathogen can cause fever, joint pain, arthritis,
bulls-eye rash
how do yuo getnthe lyme pathogen
tick bites. – from black-legged tick (also known as deer tick) – they enlarge during feeding
when do ticks bite humans
when theyre adults
transmission
pathogens much move between hosts. there is direct and indirect
direct transmission
pathogens move from one host to the next
indirect transmission
pathogens use another organism (vector) to help them move – tick is a vector
hiow many blood meals do ticks take from hosts
3
which life span of tick would not have lyme
newly hatched larva, they have to pick it up from an animl theyre getting blood from
basic run down of how the lyme transmission goes
ticks get the pathogen by feeding on an infected hiost. when the tick feeds again, it may pass the pathogen on to a new host. humans are hust accidental hosts.
lyme disease historically
lyme disease when europeans first colonzied north america was very common – then declined dramatically during 1800s
– increased again in late 1900s
wht happened that the ticks increased again
pre-1700s – forest and deer were abundant
1830 – peak forest clearing (25%) left
1850 – farm abandonment
1910 – abandoned fields
1930 – forest recovering
1960s– 75% of forest bacxk
increase in the habitat, forest, increased number of deer, which increased ticks because deer is their preferred food source.
small mammals limit tick abundance
more mice – more infected ticks – more lyme diseasef
factors that influence white footed mouse abundance affect incidence of lyme disease
coyotes vs foxes – foxes eat mice but coyotes eat foxes. because of huge exapansion, more coyotes present – therefore coyotes have negative impact on foxes, which increases abundance iin mice.
howq does lyme disease spread `
migratory birds move ticks to new locations
climate change and lyme disease
climate must be warm enough for tick survival and reproduction – as climate warms , black legged tick range is predicted to expand
