chapter 52 - community ecology Flashcards
define biological community
consists of all the populations of interacting species living within a defined area
4 types of species interactions
mutualism
- two species interact in a way that benefits fitness of both (+/+)
competition
- individuals use the same resources, lower fitness for both (-/-)
consumption
- one organism eats/absorbs nutrients from another, increasing consumers fitness, lowering victim’s (+/-)
commensalism
- once species benefits, other unaffected (+/0)
types of competition
infraspecific competition (same species)
- density dependant (cause of density dependant growth)
- intensifies as density increases
interspecific competition (different species)
- when members of different species use same limiting resources
- direct (real-time competition) vs indirect
factors that can affect competition
niche overlap
- competitive exclusion lowers carrying capacity
fundamental vs realized niche
fundamental
- total theoretical niche a species can occupy
realized
- niche species occupies as a result of forces of competition
why would species niches not fully overlap?
from their FUNDAMENTAL NICHE, species pushed into their REALIZED NICHE by factors such as competition with other species
competitive exclusion principle
when a superior species uses all of its competitor’s resources, causing inferior species to disappear
niche differentiation
natural selection against species that compete
therefore removes competitive overlap in niches
fitness tradeoff in competition
- competitive traits are only one aspect of niche
- therefore, organisms have to trade off other traits, a compromise in adaptation
e.g. organisms good at competing probably struggle with droughts and disease
RESULT: natural selection against individuals that compromise traits (NICHE DIFFERENTIATION)
types of consumption
- herbivory
- predation
- endoparasites (live inside host. simple and worm-like)
- ectoparasites (live outside hosts. harvest fluid)
- parasitoids (have endoparasite larvae) pa
types of defences
constitutive/standing defences
- always present, even in absence of predator
inducible defences
- only present when predator is present
define the two types of mimicry
constitutive defenece
- Batesian (look dangerous, aren’t dangerous)
- nontoxic prey species resemble dangerous prey species
- one species benefits - Müllerian (look dangerous, are dangerous)
- two harmful prey species resemble each other
- both benefit
constitutive/standing defences
defences always present
- cryptic colouration/object resemblance
- escape behaviour
- toxins and chemicals
- schooling + flocking
- defence armour + weapons
- mimicry (batsman and mülerian)
inducible defences
- traits produced in response to the
presence of a predator - less costly, but take time
parasites
- use consumers as biocontrol agents
- consumption is an agent of natural
selection (hosts get eaten, making it easier to spread parasite)
define mutualisms
mutually beneficial dynamic species interactions
*mutalism may fail the mutualist:
eg ants and tree hoppers - tree hoppers eat ants predator (spiders), and use ants honeydew. when spiders not present, ants dont benefit, do tree hopper-ant relationship changes to -/+ (consumption)
key aspects of community structure
- total number of species
- general types and outcomes of interactions among all species
- relative abundance of those species
- physical aspects that matter (including biotic/abiotic factors)
when multiple consumption interactions are linked…
food chain!
when multiple food chains are linked…
food web
trophic cascade
series of changes in abundance of species in a food web
usually caused by addition/removal of predator
things that impact food webs
- top down influence
- bottom up influence
- ecosystem engineers
- trophic cascade (when impacts propagate down)
define a “disturbance” in an ecological community
- strong, short-lived disruption that changes the distribution of living or nonliving resources
e.g. forest fire, epidemic, flood
impact is a function of
1. type
2. frequency
3. severity
define disturbance regimine
characteristic disturbances that affect a given community
describe how communities can develop after disturbances
depends on state of the soil
PRIMARY SUCCESSION
- organisms colonise bare mineral soil
SECONDARY SUCCESSION
- soil is already present so recovery is faster
stages of secondary succession
- pioneering species
- weedy species - early successful community
- long-lived herbaceous species - mid-successional community
- shrubs and short lived trees - climax community
- long lived trees
general development of communities after disturbances
early successional communities species
- short lived
- small size
- disperse seeds over long distances
late successional communities species
- long lived
- large
- good competitors for light and nutrients
role and types of species interactions in colonization
- succession after colonization depends more on how species interact with each other
- as species modify habitat, different traits favoured, leads to species replacement
types of interactions:
1. FACILITATION - Existing species help those arriving
2. TOLERANCE- existing species don’t affect arrivals
3. INHIBITION - presence of one inhibits the other
define species richness, diversity
richness:
# of species present in a given community
diversity:
measure of species relative abundance
definitions used interchangeably
immigration and extinction on islands as a function of…
distance
immigration decreases as population increases
extinction increases as population increases
extinction can be a function of ___
distance
the farther species immigrate, the more likely they are to go extinct
asymmetric vs symmetric competition
ASYMETRIC
- one species suffers more than another
SYMETRIC
- both species suffer fitness loss
theory of island biogeography
distance
immigration decreases as population increases
extinction increases as population increases
global patterns in species richness
- large populations tend to be species rich
- latitudinal gradient in species diversity
hypotheses for species richness
many, e.g.
- high-productivity hypothesis (increased speciation, decreased extinction)
- area and age hypothesis (historically more time for speciation to occur)
- environmental variability (eg seasons)
