Ecology Lesson 5 Flashcards
Community
Set of species in a specific location
Community Functions
- Species interactions (ie. competition)
- Energy and nutrient flows and what direction they flow.
Community Structure
- Species richness (number of species). Diverse?
- Composition (relative abundance of species). Is there rare or common species.
Community dynamics
- Change in structure or function over time (abundance and interaction, etc.)
Trohic interactions
All - and +. Related to feeding. Transfer of energy from one to another.
* Predation
* Herbivory
* Parasitism
Food webs
Represent trophic interactions. The arrows show the direction of energy flow. Made up of food chains in the web. Read from bottom to top. Bottom is the primary producers and top is usually humans. Very complex and dynamic. They can generalize groups, ie. birds.
Trophic Level
Vertical position in the food web.
Tundra food web
Herschel Island, North Yukon and Mostly short food chains. We can compare food webs in different ecosystems. It has lots of primary producers and lemmings.
Collared lemmings
eat most plants, eaten by most predators – “important.” It connects the species together. If you lose it, it turns into two food webs.
Species with a large impact
Some species play a disproportionate role in
the food web.
Domaint species
Ecosystem engineers
Keystone species
Domaint species
Large impact due to high biomass. There are a lot of them.
Ecosystem engineers
Large impact because they alter the physical environment. ie. beavers make dams.
Keystone species
- Large impact despite low biomass and abundance.
- Usually predators, have control over species that they prey on.
Otters
Top-down control
Higher trophic level reduces abundance or
biomass of lower trophic level. The impact on one trophic level on the trophic level beneath it. More herbivores = less plants.
Trophic Cascade
Impact of top predators extends to lower trophic
levels. It impacts plants despite not directly eating them. It’s why predators are important in ecosystem structure. Predators=less herbivors=more plants.
Sea otters example (in BC)
1960- no sea otters, so lots of sea urchins so less kelp. Top-down control of U and K.
1970- Sea otters return. Less urchins. Top-down control of O and U
1970-The more sea otters the more kelp (good because they provide habitat and shelter for many species). Trophic Cascade.
1990 (in alaska)- orcas started to eat sea otters, so more urchins, less kelp.
Sea otter impacts on community
- Fewer herbivores
* Sea urchins, starfish - More kelp
* More productive
* Physical structure
* Fish species richness
Atlantic coast urchin example
The Atlantic coast has no sea otters and not as big kelp beds.
Historically it was top-down with large predatory (other fish that act as each other) fish then sea urchins then kelp.
Then a trophic casacade when overfishing occurred because more sea urchins and less kelp.
Then in 1980s the urchins got a disease then more kelps. But then the urchins recover, so less kelp. (Alternating communities)
Alternating communities
The sea urchins where it fluctuates between these two kinds of ecosystems. It depends on the water temp, as the pathogen that kills the urchins is I’m the warm water.
Regime shift
Abrupt shift to a very different and persistent community. They may or may not recover. ie. kelp to barrens and corals to marcoalgaes.
What causes a regime shift?
Usually external drivers:
* Removal of keystone species
* Arrival of disease
* Climate change
* Nutrient inputs
Bottom-up control
Lower trophic level controls abundance or biomass of
higher trophic level
* E.g. primary producers limit herbivore biomass
Top-down critical points
- Top predators frequently exert top-down control
- Without predators, herbivores often have strong
impacts on primary producers.
Top-down Applications
- Wildlife management in absence of top predators (want to reintroduce them to get the ecosystem back to normal).
- Management of insect pests (use natural predators).
- Management of natural resources (ie. limiting on fishing to ensure the ecosystem doesn’t switch to a different state).
Ecosystems have an impact on what?
The rate of transmission of zoonotic diseases.
Zoonotic disease
Animals to humans.
What is Lyme disease?
it’s parasitism.
* Caused by a spirochaete
(bacterium) Borrelia burgdorferi
* Pathogen can cause fever, joint pain,
arthritis
* Bulls-eye rash.
How do you get the Lyme pathogen?
Tick bites. They live in grassy ecosystems.
* Black-legged tickn (Ixodes scapularis). Also called deer tick. Only adults bite humans.
* Enlarge during feeding.
Ticks carry it (they are a vector).
Ticks in NS
The cases are increasing. The range is expanding.
Transmission of Lyme Disease (the two types)
Pathogens must move between hosts. Ticks get the pathogen by feeding on an infected host When the tick feeds again, it may pass pathogen on to new host
Humans are just accidental hosts.
* Direct – pathogens move from one host to the next (person to person).
* Indirect – pathogens use another organism (vector) to help them move (they need to tick).
Tick meals
Larva - Birds and small mammals
Nymph - small and large mammals
Adult - Deer
Do newly hatched tick larvae have Lyme disease?
No, they have to pick it up from one of their hosts.
How long have pathogen and ticks have been around?
Pathogen (Borrelia burgdorferi)
* In N. America for >60,000 years
Ticks (Ixodes scapulari)
* In NE USA for >10,000 years
Lyme disease historically
- Lyme disease common when
Europeans first colonized North
America - Incidence declined dramatically
during 1800s - Increased again in late 1900s
Lyme disease timeline
- Pre-1700: Forest and deer abundant
- 1830: Peak of forest clearing (25% left) (so no deers)
- 1850: Farm abandonment
- 1910: Abandoned fields
- 1930: Forests recovering
- 1960s: 75% forested
Deer recovery in Connecticut
1896: ~12 deer
Today: 150,000 deer
Monhegan Island, Maine Example
It originally had a lot of ticks so they Eradicated deer
then Lyme disease disappeared. Deer have impact on tick abundance and transmission to humans.
Small mammals limit tick abundance
More mice
-> more infected ticks
-> more cases of human Lyme
Factors that influence white-footed mouse abundance affect incidence of Lyme disease – coyotes vs. foxes. Coyotes have a negative impact on foxes=more mice.
How does Lyme disease spread?
- Migratory birds move ticks to new locations.
- First infected tick in NS found on migratory bird
(Bon Portage Island, 1999).
Eventually enough ticks arrive to establish populations in new areas.
Forest recovery on ticks
- Deer recovery
- Tick recovery
- Number of ticks hitchhiking on birds increases
Ecological interactions are key to understanding disease dynamics?
- Deer necessary for ticks – forest recovery led to more deer.
- Small mammals limit tick numbers (top-down).
- Migratory birds facilitate tick dispersal (they move them).
Climate change and Lyme disease
- Climate must be warm enough for tick survival and reproduction.
- As climate warms, black-legged tick range predicted to expand.
