Unit 4: Ecology Flashcards
Population
Group of individuals of the same species living in the same area
Measuring populations size: indirect indicators
- Less resources, less time, less costly
- Examples include
— # of nests, borrows, tracks
— Catch per unit effort (CPUE)
— Mark-recapture methods
Mark-recapture methods
- capture + mark animals
- Take a second sample: based on how many marked are in new sample, can estimate pop. size
s = # marked and released in 1st sample
n = number of individuals in 2nd sample
x = total # of individuals already marked in second sample
estimate population size = N
Assumption: x/n = s/N
N = (s)(n) / x
Mark-recapture assumptions
- Marked and unmarked individuals = same probability of being ‘captured’
- Marked individuals have mixed completely back into the population
- No individuals are born, die, immigrate, or emigrate during the sampling interval (short sampling interval)
Exponential growth model
dN/dt = r N
dN/dt (delta pop. size/ delta time) = rate of change in a population
N: current population size
r: growth rate
larger r = faster growth
Why does the population growth rate slow?
- Resources become limited
- Food and space
- This is because birth rates decline and/or death rates increase
- Density-dependent birth or death rates rugulate populations around an equilibrium
What is carrying capacity?
- Carrying capacity (K) is the # of individuals of a pop. that an environment can support; birth rate (b) = death rate (d)
Logistic growth model
dN/dt = rN (K-N/K)
- New term (K-N)/K reduces the rate at which the population grows as N increases
- If small N compared to K, r is larger
- If large N compared to K, r is smaller
- If N = K, the pop. stops growing
Regulation processes
Bottom-up process: regulated by resources, they are the predators (top) eating food (bottom)
Top-down process: regulated by predation, prey (bottom) getting eaten (top)
Life History
Traits that affect an organism’s schedule of reproduction and survival
Three main variables of life history
- Age of first reproduction
- How often organism reproduces
- How many offspring produced per reproductive episode
Reproduction trade-offs
- More offspring means less energy put into each one
- Alternatively, energy can be used to:
1. Increase offspring size
2. Provide parental care
therefore more likely to survive - Many offspring = each offspring low quality (many do not survive)
- Few offspring = Each offspring high quality, each likely to survive
r vs. K strategists
1) r strategists: maximize # offspring
- Smaller offspring
- No parental care
2) Maximize offspring survival
- Larger offspring
- Parental care
r/K strategists + environment
1) r strategy advantageous where quality matters little
- physically harsh environment:
- most offspring die anyway
- unpredictable environment:
- Most offspring will not survive
2) K-strategy advantageous where quality matter a lot
- Crowded or competitive environments:
- Stronger more likely to survive
- predictable environment
- Provisioning/caring increases survival
r/k stragists + habitats
r strategists - habitats that are:
- Open/disturbed
- Temporary
- Unpredictable
K strategists - habitats that are:
- Permanent
- Crowded
Community
A group of populations of different species that live close enough to interact
Species interactions
- Competition
- Mutualism
- Commensalism
- Parasitism
- Predation
- Herbivory
Competition
- Individuals of 2 species competing for resources required for growth and survival
- Both species do better without the other
- One will eventually outcompete the other (competitive exclusion)
Interspecific competitors
- Use the same resource
- Resource is in limited supply
- Intertidal - space is the limited resource
Competition of resources:
—Lower birth rate (b)
—Higher death rate (d)
—Slower population growth (r) - Ex. Barnacles
Ecological niche
- The position of a species within the ecosystem
- Its role in the ecosystem
- Conditions necessary for its survival
Realized vs. fundamental niche
- Realized niche: the ‘observed’ niche that it occupies in the wild
- Fundamental niche: the conditions in which it can survive and reproduce
Competitive exclusion principle
- If two species compete for one resource, the better competitor will eliminate the other
- Species must occupy somewhat different niches
(Two species cannot coexist in a community if their niches are identical)
Character displacement
Evolution differences in morphology and resource use as a result of competition
- Can result in resource partitioning (one or more significant differences in their niches)
Symbiosis - mutualism
- Help each other
Symbiosis - Commensalism
- One organism helped by another, one is unaffected
Symbiosis - parasitism
- One organism (parasite) gets nourishment for the other (host)
- One benefits and the other gets harmed (rarely killed)
Endoparasites
Parasites live within the body of their host
Ectoparasites
Parasites feed on the external surface of a host
Pathogen transmission
1) Direct: pathogens move from one host to the next
2) Indirect: pathogens use another organism (vector) to help them move (e.x. Lyme disease in ticks)
Brood parasitism
- Brood parasitic birds lay their eggs in the nest of others
- Pass on the cost of rearing their offspring onto another individual (host)
- Can be intraspecific or interspecific
Predation
Predator kills and eats prey
Evolutionary arms race
- Predators have adaptations for eating
- Prey have adaptations to escape/avoid being eaten
Herbivory
- Exploitative interaction (+/-) where an organism eats parts of a plant or algae
- Most herbivores are insects (e.g. grasshoppers and beetles)
- Can significantly influence their environment
Food webs
- Made up of food chains
- Food webs represent trophic interactions
- (Vertical) position in the food web is called the ‘trophic level’
Collared lemmings
Eat most plants, eaten by most predators
Focal species
Some species that play a disproportionate role in the food web
Types of species with a large impact
1) Dominant species (high biomass)
2) Ecosystem engineers (alter the physical environment)
3) Keystone species: despite low biomass and abundance, usually top predators
Top-down control
Higher trophic level reduces the abundance or biomass of lower trophic level
- Ex. more herbivores, less plants / more carnivores, less herbivores, more plants
Trophic cascade
Impact of top predators “cascades” down to lower trophic levels
Sea Otter
- Keystone species
- Impact on community:
1) fewer herbivores (sea urchins, starfish)
2) More kelp - More productive
- Physical structure
- Fish species richness
Regime shift
Abrupt shift to a very different and persistent community
What causes regime shifts?
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
- Ex. primary producers limit herbivore biomass
Species richness
Number of species present in a community
Disturbance
An event (ex. storm, overgrazing, human activity) that changes a community by removing organisms or altering resource availability (species richness may increase, decrease, or remain the same)
Why should we care about biodiversity?
- Biodiversity is tied to ecosystem services, which are benefits people obtain from ecosystems
- Biodiverse ecosystems = more carbon sequestration
- Diverse habitats provide natural coastline protection
- Diverse habitats provide livelihoods (ex. fisheries)
- Diverse habitats provide a sense of place + well being
Ecosystem
Organisms and abiotic environment
Ecosystem Function
- Species interactions (connections between components)
- Energy and nutrient flows
Connections in an ecosystem
- Organisms to organisms
- Organisms to the physical environment
Energy flows
- Ecosystems (and life) are powered by the sun
- Primary producers capture radiant energy and store chemical energy (in molecular bonds in organic compounds)
- Ecosystems transfer chemical energy through consumption (transfer to consumers) and death (transfer to detritus)
- Ecosystems lose heat energy through respiration
- Energy transfer between trophic levels is typically only 10% efficient
Nutrient flows
- Circular flow of Nutrients: nutrients mostly retained. Cycle between organisms and physical environment
Decomposers in nutrient cycling
- Invertebrates, fungi, bacteria
- Obtain chemical energy and nutrients from detritus (dead organisms)
- Return some nutrients to physical environment
Carbon Cycle
Plants get CO2 from atmosphere and convert to organic carbon (org C). Org C transferred among organism. CO2 returned to atmosphere through respiration.
Carbon reservoirs
C is mostly stored in rocks and sediments. The rest is located in the ocean, atmosphere, and living organisms
Range shifts
- Climate change
- Species redistribute to stay within climatic niche
Generally leads to movement away from equator and towards poles - On avg., 17 km/decade (terrestrial), 72 km/decade (marine)
- Also deeper (marine) / higher (terrestrial)
Coral bleaching
- Warming water causes corals to lose their symbiotic algae
- Repeated bleaching can permanently alter coral community
- Among the greatest threats to coral reefs today
- Unclear whether corals can adapt fast enough
Ocean acidification
- Input of carbon dioxide reduces pH (more H+) and carbonate ion concentration:
- Calcifying organisms (e.g. corals) have trouble building and maintaining calcium carbonate skeletons
Nitrogen
- Forms of organic nitrogen: DNA, RNA, proteins
- Crucial for all living organisms
- Required for photosynthesis
Bacteria-driven nitrogen cycle
- N-fixation: N2 - NH4-
- Nitrification: NH4- - NO3-
- Denitrification: NO3- - N2
Agriculture and N
- Agriculture increases rates of N-fixation by
1. Growing legumes
(soybeans, peas, beans)
2. Manufacturing fertilizer
Legumes and N
Root nodules contain N-fixing bacteria (Rhizobium) (symbiosis - mutualism)
Consequences of N fertilizer
Long term impacts of excessive nitrogen inputs:
- High nitrate (NO3-) levels in soil water - can be toxic
- Pollution of aquatic ecosystems
(Unused nitrogen enters streams and rivers)
Coastal marine environments and N
- Eutrophication: Excessive primary production (algae) due to overload of nutrients
- Decomposition of algae leads to oxygen (O2) depletion
- Dead zone: low O2, fish and others die
Ecosystem health
- An ecosystem processes and transfers energy and nutrients
- Fueled by energy from outside the ecosystem
- Cycle and recycle nutrients from and to the physical environment
- An ecosystem might be ‘unhealthy’ if it is less able to:
- Obtain or transfer energy
- Cycle or retain nutrients
Reasons to care about ecosystem health and function
- Feeding ourselves
- primary production: how fast can we grow food?
- Secondary production: how efficiently can we feed livestock animals? - Natural ecosystems
- Primary production: plants/tree abundance and recovery after damage
- Secondary production: Animal diversity and abundance
- Decomposition - nutrient supply - We are changing the rates
- Deforestation
- Use of fertilizers
- Greenhouse gas emissions and climate change
Measures of ecosystem function
- Rate of primary production
- rate that primary producer biomass is built - Rate of secondary production
- rate that consumer biomass is built - Rate of decomposition
- rate that inorganic nutrients are released from detritus
Net Primary Production (NPP)
- Rate that plant biomass increases in an ecosystem
- Biomass: Amount (mass) or organic matter present in an ecosystem
Gross primary production (GPP)
Total light energy captured by plants
Autotrophic respiration (Ra)
Energy lost due to plant respiration
NPP = GPP - Ra
Net Ecosystem Production (NEP)
- Energy (biomass) accumulated in all ecosystem components (per unit time)
- Plants capture energy
- Energy stored as biomass in all organisms
- Heat energy lost from all organisms
NEP = GPP - RT
Positive NEP
- Ecosystem biomass is increasing
- Ecosystem absorbs more CO2 than it releases
- Helps lower atmospheric CO2 (climate change)
