Ecology: Lecture 5 Flashcards
What are communities?
A set of species within an ecosystem
Function of communities?
- Species interactions
- Energy and nutrient flows
Structure of communities?
- Species richness (number of species)
- Composition (relative abundance of species)
Dynamics of communities?
- Change in structure or function over time
Species interactions (types)
- Competition ( - - )
- Mutualism ( + + )
- Commensalism ( + 0 )
- Trophic interactions ( + - )
- Predation
- Herbivory
- Parasitism
What are trophic interactions?
- Related to feeding. Transfer of energy from one species to another (prey-predator).
Ex. Predation, herbivory and parasitism
Food webs represent?
They represent simplifications of trophic interactions.
Trophic levels?
The vertical position in the food web is called the trophic level.
Food webs are made up of?
Food chains.
Food web arrows represent?
The direction of energy flow.
Ex. Squids ~> leopard seals
Collared lemmings?
They eat most plants and are eaten by most predators.
This makes them “important” for the food web.
Large impact species?
Some species play a disproportionate role in the food web.
Dominant species- Large impact?
They are a food source for many predators
- Large impact die to high biomass - many of them and high abundance
Ecosystem engineers - Large impact?
Large impact because they alter the physical environment.
Keystone species - Large impact?
- Large impact despite low biomass and abundance
- Usually predators
Are predators really important?
Sea otters
- eat sea urchins, mussels, etc.
- not “apex” predators
Atlantic cod
- eat crustaceans, herring, other small fish.
Top-down control?
High trophic level reduces abundance or biomass of lower trophic level.
affect of top-down control?
More plants without herbivores.
- More herbivores means less plants
Directions of energy flow vs. direction of impact?
IMPACT: Herbivores ~> PP
ENERGY: PP ~> Herbivores
Trophic cascade?
Impact of top predators extends to lower trophic levels.
- Effect cascades down the levels.
Trophic cascade impact - visual?
Predators impact herbivores and then the herbivores have reduced grazing.
- Fewer herbivores and MORE plants
Trophic cascade impact - ecosystem structure?
Predators are important in terms of ecosystem structure because they impact directly through predation and indirectly through trophic cascades
- extensively impact ecosystem’s look
British Colombia 1960s?
No sea otters.
Sea urchins eat kelp, causing them to be very scarce. High density of urchin barrens.
British Colombia 1970s?
Sea otters return.
Top down control.
- Sea otters lower sea urchin population which increases kelp population. Re-established kelp forests.
- A transition in the environment was brought by top-down control and trophic cascade.
Trophic cascade?
Impact of top predators “cascades” down to lower trophic levels.
Sea otters as a keystone species?
Have a huge impact on the community!
- Fewer herbivores (sea urchins and starfish)
- More kelp (more productive, physical structure and fish species richness)
Alaska 1990s?
Urchin barrens returned. Why?
Orcas became more prevalent, switching the dietary preference of the community.
- Orcas decreased otters which increased urchins with reduced kelp again.
Atlantic coast?
No sea otters - but still kelp beds.
Large predatory fish (wolffish and cod) take the role of the otters.
Atlantic coast cascade?
Fish are overfished and that leads to less kelp again.
Atlantic coast recently?
Urchin barrens got diseases, leading to kelp beds being prevalent, urchins recovered leading to urchin barrens being most prevalent again.
Regime shift?
A type of ecosystem shifts, change in the physical community may or may not recover.
- Removing a keystone species might cause a regime shift.
Examples of regime shifts?
Climate change (coral bleaching)
Nutrient inputs (competition)
What is the situation on the Atlantic coast?
Urchin barrens go to kelp beds and kelp beds go to urchin barrens.
- REGIME SHIFT
Definition of a regime shift?
Abrupt shift to a very different and persistent community.
Ex. Kelp ~> barrens
Ex. Corals ~> macroalgae
What causes regime shifts?
Usually external drivers:
- Removal of keystone species
- Arrival of disease
- Climate change
- Nutrient inputs (sewage, runoff changes competition)
Atlantic NS kelp forest dynamics?
Alternating community (urchin barrens to kelp forest) despite historic top-down control.
Top-down control?
Higher trophic level controls abundance or biomass of lower trophic level
* E.g. herbivores limit primary producer biomass
Bottom-up control?
Lower trophic level controls abundance or biomass of higher trophic level
* E.g. primary producers limit herbivore biomass
Critics points of top-down control?
- Top predators frequently exert top-down control
- Without predators, herbivores often have strong impacts on primary producers
Applications of top-down control?
- Wildlife management in absence of top predators
- Management of insect pests
- Management of natural resources
The ecology of Lyme disease?
Parasitism ( + - )
- Ecological interactions affecting host species of Lyme disease.
What is Lyme disease?
- Caused by a spirochaete (bacterium) Borrelia burgdorferi
- Pathogen can cause fever, joint pain, arthritis
- Bulls-eye rash
- can be resolved with antibiotics
How do you get the Lyme pathogen?
Tick bites from a black-legged tick or deer tick (lxodes scapularis).
Enlarge during feeding.
How is Lyme increasing?
Cases are increasing and range is expanding.
Transmission of Lyme?
- Pathogens must move between hosts
- Direct – pathogens move from one
host to the next - Indirect – pathogens use another
organism (vector) to help them move
Ticks take three blood meals from hosts?
Larva ~> Birds and small mammals
Nymph ~> Small and large mammals
Adult ~> Deer
Humans are essentially “accidental” hosts.
Newly hatched tick larvae?
Do NOT have Lyme. They pick it up from another animal
Process of getting Lyme?
- 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
Pathogen and tick have been in North America for a long time?
Pathogen (Borrelia burgdorferi)
* In N. America for >60,000 years
Ticks (Ixodes scapulari)
* In NE USA for >10,000 years
* So what is going on?
Lyme disease historically?
- Lyme disease common when
Europeans first colonized North
America - Incidence declined dramatically
during 1800s (change in habitat and affected food preference) - Increased again in late 1900s
What happened?
Pre-1700 (Forest and deer abundant)
1830 (Peak of forest clearing (25% left))
1850 (Farm abandonment)
1910 (Abandoned fields)
1930 (Forests recovering)
1960s (75% forested)
Deer recovery?
Connecticut
1896: ~12 deer
Today: ~150,000 deer
This is why they are an ample food resource for ticks.
Deer are the preferred host of adult ticks (Maine)?
Monhegan Island, Maine
- Eradicated deer
- Lyme disease disappeared and there have only been 1-2 cases since they were removed.
Small mammals limit tick abundance?
More mice
- More infected ticks
- More cases of human Lyme
What then affects Lyme disease incidence?
Factors that influence white-footed
mouse abundance affect incidence
of Lyme disease – coyotes vs. foxes
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)
Forest recovery (NE USA)?
Eventually enough ticks arrive to establish populations in new areas.
- Deer recovery
- Tick recovery
- Number of ticks hitchhiking on birds increases
- Change in habitat
- Forest recovery
- Abundance changes
Ecological interaction in understanding disease dynamics?
- Deer are necessary for ticks - forest recovery led to more deer
- Small mammals limit tick numbers
- Migratory birds facilitate tock dispersal
Climate change and Lyme disease?
- Climate must be warm enough for tick survival and reproduction
- As the climate warms, black-legged tick range is predicted to expand.
- Ticks have a niche (set of conditions affecting transmission and expansion)
As of 2025…?
Growing extremely fast, important for human health and zoonotic diseases.
What else would this impact?
Also impacts malaria and its transmission through mosquitos - 10s of millions of people affected.
