BIOL 230 - MT 2 Flashcards
Communitites
Groups of interacting species in the same place at the same time.
Taxonomic affinity (being of the same taxa), guild (Species that use the same resource), functional group (Similarly functioning, e.g, nitrogen fixing plants).
Key elements of community structure:
Species composition
Species’ ecological inter-relationships
Species diversity
Community structure
Set of characteristics that shape communitites.
Descriptive in nature, but provides the basis for hypotheses and experiments to understand how communities work.
Species richness
The number of species in a community
Species evenness
Relative abundances compared wth one another.
What two aspects does species diversity combine?
Species richness and evenness
Biodiversity examples
Genetic diversity within a population
Diversity of communities at larger scales
Species evenness visualized with rank abundance curves
The steeper the slope the less even the community.
Species accumulation curves
Species richness plotted as a function of total number of individuals counted.
When most or all species in the community are accounted for the graph levels out.
Species-area relationship
Species richness increases with area sampled
In the theory of island biogeography which islands have the steepest curve on a species richness to area graph?
Islands far away had the steepest line and near islands had the flattest.
What did the island biogeography theory state
There appeared to be an equilibrium number of species on the islands which was dependent on their size and distance from the mainland.
Change in species richness is equal to what?
Speciation - extinction + immigration
Describe the equilibrium model of biogeography
There is a point where the immigration and extinction rates are equal.
If S drops below the equilibrium value, there are more resources and space for the entry of new species.
If S increases above the equilibrium the likelihood of species going extinct increases.
The effect of S on extinction rates (equilibrium model).
When S is small, life is easy, low competition and high population sizes means the extinction rate is low.
As S gets larger the more resources will be used up. Species will experience a reduction in density, increasing extinction probability.
When S is very high any disturbance or random fluctuations in population size is increasingly likely to wipe out the small populations. High extinction rate.
What is the main thing that affects extinction rate?
Area.
Rates are expected to shift higher on smaller islands but remain lower on large islands.
Effect of S on immigration rates
When S is small, most newly arriving individuals will represent a new species; immigration rate of new species is high.
As S increases, the species immigration rate decreases because the odds of a newly arrived individual representing a new species is lower.
At high S values there are fewer potential new species left at the source so “new” species run out. Immigration rate approaches zero.
What is the immigration rate mainly influenced by? (Islands)
Isolation distance.
The immigration rates on further islands are lower as the island is harder to reach. Islands closer to the source have higher immigration rates.
Biogeography
Patterns of species composition and diversity across geographic locations.
In general what is the correlation between latitude and species richness?
Lower latitudes have many more and different species than higher latitudes.
Can also vary by region of the world even at similar latitudes.
Species diversification equals:
Speciation rate - extinction rate
What are the three main hypotheses on why the tropics have the highest species richness?
Diversification rate hypothesis
Diversification time hypothesis.
Carrying capacity hypothesis
Diversification rate hypotheses
The tropics have the most land area on Earth with stable temperatures.
Cradle hypothesis: Higher speciation rate in tropics
Museum hypothesis: Lower extinction rate in the tropics
Carrying capacity hypothesis
Due to higher productivity in the tropics, the tropics have a higher carrying capacity than temperate areas.
Could also explain the reverse latitudinal pattern seen in sea birds; coastal oceans are most productive at higher latitudes.
Diversification time hypothesis
The tropics have been more climatically stable over time, allowing species to have had more time to evolve.
Temperate and polar regions have undergone severe climatic changes.
Gamma diversity
Regional patterns of species diversity
Driven by dispersal across the landscape
Alpha diversity
Local patterns of species diversity and composition
Driven by physical conditions and species interactions.
Beta diversity
Local and regional scales are connected by turnover; the difference in species diversity and composition from one community type to another across the landscape.
Asymmetric interspecific competition
Often the effects of competition is unequal, or asymmetrical and one species is harmed more than the other.
Can lead to one species driving another to extinction when they share the same limited resource.
Competition definition
A non-trophic interaction in which individuals of the same species or different species are harmed by their shared use of a resource that limits their ability to grow,reproduce or survive.
Intra vs interspecific competition
Intraspecific competition is competition between individuals of the same species. Leads to density dependent population growth and sets K.
Interspecific competition is between individuals of different species. (General focus when considering community structure and species richness).
Exploitation competition
Reducing access to a recourse by reduction of the availability of that resource.
Indirect effect
Interference competition
Reducing access to a resource by directly interfering with a competitor.
Direct effect.
Competition exclusion principle
Two species that use a limiting resource in the same way cannot coexist indefinitely.
Predicted outcome of two species using the same limiting resource in the same way.
Fundamental niche
The full set of resources, plus other biotic and abiotic requirements of a species, that allow it to survive, grow and reproduce.
Realized niche
The restricted set of resources or conditions a species is limited to, due to species interactions.
Resource partitioning
Species use a limited resource in different ways.
Example: Galapagos finches have small beaks for small seeds and some have large beaks for larger seeds.
Character displacement
The shift in phenotypes through time in response to competition.
Reduces the strength of interspecific competition.
Factors that determine how strong or weak competition is, and how asymmetrical it is.
The degree of overlap in resource use.
How good you are at finding, acquiring and defending a resource and how fully you can deplete it.
Competition coefficient alpha
of individuals of species 1 that are lost for every individual of species 2
Per capita negative competitive effect of species 2 on species 1
Competition coefficient Beta
of individuals of species 2 lost for every extra individual of species 1.
Per capita negative competitive effect of species 1 on species 2.
What can be determined if alpha and beta are «1
Species 2 has a much greater effect on itself compared to the effect species 1 has on it.
Species use resources very differently
How can two species coexist if beta > 1
Alpha is sufficiently low and K2 is enough higher than K1.
Interspecific interactions
Interactions between species that can affect growth, survival and fitness
Amensalism
One species affected negatively, one not affected at all.
Predation and types of predation
Trophic interaction in which an individual of one species consumes some or all of another species.
Carnivory - predator and prey are animals
Herbivory - Predator is animal, prey are plants or algae
Parasitism - Predator is a parasite and lives on or in the prey and consumes certain tissues. May or may not kill the host. Some cause disease (pathogens).
Advantages and disadvantages of carnivory
Animal prey are generally more nutritious but require more energy expenditure to catch.
Ways prey avoid being munched
Crypsis (camo)
Habitat selection (accessibility)
Morphological defences
Chemical defences
Predation affect on competitive exclusion
Predation can disrupt competitive exclusion.
Example: Pisaster preferentially eat mussels and large barnacles. This prevents these two larger species from excluding smaller barnacles.
What range of species are commonly parasitic?
Protozoans, Platyhelminthes, Arthropods, Fungi, Bacteria, Viruses
Advantages and disadvantages of endoparasitism
Advantages: Ease of feeding, protection from external environment, safer from natural enemies.
Disadvantages: Dispersal, vulnerable to host immune system.
How do endoparasites overcome dispersal difficulties?
Enslavement, diarrhea, specialized life stages.
Advantages and disadvantages of ectoparasitism?
Advantages: Ease of dispersal, safe from host immune system
Disadvantages: Vulnerable to natural enemies, exposure to external environment, feeding more difficult.
Parasites typically feed on only one host or a few host species. How is this different from the host species?
host species have multiple parasite species.
What percentage of species can be classified as symbionts?
50% or more
Pathogen vs parasite?
A pathogen is a parasite that causes disease.
dI/dT = B S I - m I
The change in density of infected individuals over time = (The transmission coefficient * the density of susceptible individuals * the density of infected individuals) - (The combined host death and recovery rate * the density of infected individuals)
What is the transmission coefficient?
Coefficient describing how many encounters end in transmission
When will a disease become established?
When the density of infected individuals in a population increases over time.
dI/dT > 0
What is the meaning of S > St
High density of susceptible hosts.
If St > S there is a low density of susceptible hosts.
A negative interaction that isn’t trophic?
Antagonism
Positive interactions (Facilitation)
No species is harmed and the benefits are greater than the costs for at least one species.
Two types of facilitation?
Mutualism - Mutually beneficial for two individuals (+/+)
Commensalism - One species benefit, one is not harmed (+/0)
Obligate interactions
Not optional for either species.
Facultative interactions
Optional interactions and few signs of coevolution
Relative neighbour effect
Target species growth with versus without neighbours present.
Generally positive at high elevation, negative at low elevation.
Competition more common in less stressful environments.
Trophic mutualists
A mutualist receives energy or nutrients from its partner
Mycorrhizae
Habitat mutualisms
One partner provides the other with shelter, living space or favorable habitat.
What is different about an interaction web compared to a food web?
An interaction web includes non-trophic horizontal interactions as well.
Indirect interactions
The relationship between two species is mediated by at least one additional species.
Competitive networks
Interactions among multiple species in which no species wins every pair-wise competitive interaction.
A outcompetes B, which benefits C, which outcompetes A, which benefits B, which outcompetes C, which benefits A…..
Trophic cascade
Carnivore eats herbivore which has a positive effect on a primary producer.
Top-down effect.
Trophic facilitation
A consumer is indirectly facilitated by a positive interaction between its prey and another species.
Density mediated indirect interaction
Occurs when species A affects the density of species B, with consequences for species C.
Trophic cascade
Trait-mediated indirect interaction
Occurs when species A affects the behaviour of species B with consequences for species C.
Example: Jays stay away from hawks nests allowing humming birds to make nests near the hawk nest.
Keystone species
Large effect in proportion to their biomass or abundance.
Ecosystem engineers
Create, modify or maintain a physical habitat.
Examples: Coral providing physical structure or beavers building dams.
Foundation species
Provide habitat or food
Typically the species contributing the most spatial structure. Large effect on communities due to their size and abundance.
Example: Trees, kelps, corals
Disturbance definition
An abiotic event that physically injures or kills some individuals and creates opportunities for other individuals to grow or reproduce.
Succession
Change in the species composition of communities over time as a result of a variety of abiotic and biotic agents of change
Primary vs secondary succession
Primary starts from scratch and occurs when new substrate becomes available for the first time. Lava flows, rock fractures.
Secondary follows a disturbance that leaves some components of a community.
Models of succession
Facilitation - Early successional species speed succession by improving conditions for later colonists.
Inhibition - Early successional species slow succession by interfering with later colonists.
Tolerance - Early successional species have neither a positive nor negative influence on later colonists.
Traits of early successional species
R selected - good dispersers with high reproductive rates, fast growing and early maturity.
Traits of late successional species
K selected - Good competitors, slow growers, later maturity and long-lived,
Which type of successional species would you expect to find in highly disturbed habitats?
Early successional species
At what disturbance frequency would we expect the highest diversity?
In between rare and common where early and late successional species are present.
Diversity peaks at intermediate levels of disturbance when:
Competitively inferior species are better at colonizing new patches or competitively inferior species are more resistant to disturbance.