final Flashcards
what is Hubbell’s Unified Theory of Biodiversity and Biogeography
that all species are functionally equivalent and have an equal chance of colonizing an open space
niches are functionally equivalent
offspring and immigrants all compete for open spaces
what is point mutation (v)
per capita speciation rate
how does the absence and presence of niche differences affect a species growth rate
when niche differences are present: growth rate declines with increased abundance
when absent: species abundance has no effect on growth rate
what is a metacommunity
set of communities linked by dispersal pf one or more of their constituent species
what is a regional species pool
set of species found in a region
what is a local species pool
sunset of regional pool found in local community
what are the results of neutral theory in a community
dominance increases are rarer species goes extinct
species diversity in a local community is maintained by immigration
regionally abundant species tend to be locally abundant
what is island biogeography theory
how big an island (or isolated part of mainland) and how far away it is determines the species richness there
what is facilitation (positive interactions)
encounters between organisms that benefit at least one of the individuals and harms neither
can be direct or indirect
what is mutualism
facilitative interaction where both species benefit
how does facilitation change the view of the niche
makes realized niche bigger than fundamental niche
when are positive interactions most common
under harsh environmental conditions
or extreme stress
what is the stress gradient hypothesis
about relative importance of competitive or facilitative interactions changes along a gradient of environmental harshness
competitive interactions should dominate in benign environments
facilitative interactions should become more important in stressful environments
how does relative neighbour effect change with changing environmental effects
increased environmental severity: positive (facilitation)
decreased environmental severity : negative (competitive)
what is the Hairston smith slobidkin hypothesis (HSS)
top down approach
carnivores, having no predators, are limited by food
herbivores are held below carrying capacity by by predators
plants aren’t controlled by herbivores and are abundant
what did Oksanen propose about atrophic levels
biomass at each trophic level should change as potential productivity increases
as potential primary productivity increases the number of possible trophic levels increases
biomass at each trophic level changed depending on number of trophic levels
bottom up approach
what does oksanen predict in a 3 trophic level community
As potential primary productivity increases :
producer biomass increase
herbivore biomass remains constant
carnivore biomass increases
what is a trophic cascade
indirect/direct effects a predator has on the density or behaviour of species in lower trophic levels
how do cascades differ in terrestrial and aquatic systems
weak in terrestrial
variable in aquatic systems
when do cascades only occur
- cascades/top down effects occur only when :
- direct effects are strong
- producer densities are not limited from bottom up
what make strength of predator-prey interactions vary
predator functional response
body size
energetic requirements
herbivore vulnerability
primary producer palatability
what do food chains represent
transfer of energy between trophic levels in a community
what is a trophic level
identifies a species position in the food chain
what trophic level is the base of the food chain
primary producers
how can food chains be described
number of trophic levels
level of connectance
link density
what is connectance
fraction of all possible links that are realized
what is link density
mean distance between all nodes in a web
how many trophic levels is rare in a community
when does it occur
3 (producer, herbivore, carnivore)
occurs when productivity is low (ex: dessert, Arctic)
how many trophic levels is common
4, 5, 6
what are the hypothesis of food chain length
- energy limitation / productivity hypothesis : since energy is lost at each level, length is limited by available energy
- ecosystem site hypothesis: larger ecosystems can support more species, which results in more links, leading to longer food chains
- productive space hypothesis : productivity and size work together to determine length
- dynamic stability / disturbance hypothesis: since longer chains are less stable, food chain length will be an outcome of what is feasible and and the frequency of disturbance
what is the 10% law
only 10% of energy is transferred to next trophic level
what determines the amount of energy reaching each trophic level
NPP and efficiencies
who are most efficient at assimilation
least efficient
animals are most effect
plants and bacteria mid
detritus are least
why do carnivores have higher assimilation efficiency than herbivores
food easier to digest and higher in energy
what direction do arrows in web point
towards consumer
what is resistance
measure of the ability of a community to avoid change
what is ecological resilience
how far a community can be disturbed and return to its original state
what is engineering resilience
time it takes a community to recover
what is a community / Jacobean matrix
matrix describing interaction strengths in a food web
what are the beliefs of relationship between diversity/complexity and stability
diversity = stability
- simple communities show greater fluctuations in species abundance and are more vulnerable to invasion (Elton)
- more complex communities buffered from species loss (MacArthur)
- complexity, weak interactions, and type 3 (adaptive foraging behaviour) stabilizes food-webs (McCann)
diversity = less stable
- communities with more species and links are less stable (May)
- increased diversity, trophic levels and connectance reduced stability (Primmer and Lawton)
how can diversity both benefit and harm stability
depends how you look at stability
if looking at ecosystem level: since if species vary in their response to environmental fluctuations, so increased abundance of one species can compensate for decreased abundance of another
If you are looking at the species level: since there is a max number of individuals that can live in a community, the more species richness there is the less of each species there can be. The smaller population size can then make that species more likely to go extinct
what did primm and lawton predict about resilience and already stable food webs
adding trophic levels decreased resilience
increasing connectance increased resilience
what is a bipartite network
illustrate connections between 2 trophic levels or between mutualists
what is persistence
proportion of initial species that remain in the system
what is nestedness
degree to which generalists associate with all species
specialists associated with generalists
what is modularity
the degree to which species associate with species within their group more than in other groups
how do trophic networks differ from modular networks
trophic networks are less connected and more modular
mutualistic networks are more nested
how does modularity effect persistence and resilience in mutualistic networks
both reduce
how does nestedness effect persistence in trophic networks
reduces persistence
how does connectance effect persistence and resilience in both mutualistic and trophic networks
mutualistic: promotes both
trophic: reduces both
why doesn’t productivity have an alternating effects on the biomass of adjacent trophic levels
trophic levels aren’t homogenous
a shift in potential productivity can shift from better resource competitor to more predator-tolerant species
what is the green channel
live consumer system
what is the brown system
decomposer or detrital system
what channel is more productive
green channel is faster (more productive)
brown channel is slower (lower biomass turnover)
what channel is more species rich, with more links, and weaker interactions
brown
what is ecological subsidy
the flux of organic matter/nutrients from a donor population to a recipient one
what is an ecotone
transition area between biomes and ecosystems
what is allochthonous
originating from outside the community
what is an autochthonous
originating in community where found
what can using resources from multiple ecosystems do
stabilize rapidly changing environments
what is the prediction in looped food webs
energy flow through brown channel increases abundance of top predator
top predator prefers herbivores prey over detrivore prey
detrivores increase in abundance as detritus builds up
why are looped webs linked at top and bottom
`linked on top by generalist predator that eats both herbivores and detrivores
bottom: since detritus is made of decaying organic matter
what causes the predicted inverse response of detrivores and herbivores to nutrient enrichment
since energy flow through detritus pathway is expected to increase abundance of top predator who prefers to eat herbivores
what is expected about diet of predators in response to nutrient enrichment (brown and green model) why
larger portion of diet comes from brown channel
as predators increase in abundance there is more competition for their preferred prey (green)
what is apparent competition
form of competition where species/individuals indirectly compete since both are prey to same predator
what link ecosystems
allochthonous inputs
what does species diversity in slow channels lead to
skewed distributions of interaction strengths that help stabilize entire ecosystems
what are responses in primary productivity the result of
multi channel control
what are ecosystem functions
the benefits people obtain from the ecosystem
what are the categories of ecosystem services
provisioning services: food, water, raw materials
cultural services: non-material services that provide spiritual, aesthetic, or recreational opportunities
regulatory services: control climate, and buffer against disasters, purify water
supporting services: support other services such as nutrient cycling, soil formation, primary productivity
what model helps us understand how many species we need
rivet redundancy
how does diversity effect ecosystem function
niche complementarity: species use different resources, so communities with more resources use more
facilitation: some species alleviate environmental conditions for other species
sampling/selection effect: having more species increases likelihood of having an effective one
what can positively effect the strength of complementarity effects between diversity and function
time and habitat heterogeneity
are sampling effects more or less important in aquatic environments
less
what is the biotic resistance hypothesis
ecosystems with high biodiversity are more resistant against immigration
what are portfolio effects
describes the degree to which diversity reduces variability in ecosystem service
more diverse portfolio fares better when conditions are variable
when can diversity stabilize temporal diversity
when there is variation in response to environmental conditions
what is a regime shift
a change from one community to another
what is a tipping point
critical threshold at which a system undergoes a regime shift
when are abrupt changes easily reversible
when are they hard
easy: if communities continue along a single path
hard: communities differ in their response to environmental conditions
what creates a hysteresis loop
delayed response to forward and backward changes in environmental conditions
when are alternative stable states possible
in a hysterisis loop
what must be shown to demonstrate alternative stable states
- communities must have an equilibrium support
- move to a second equilibrium point after a disturbance
- remain in alternative state after disturbance is gone
- abiotic environment isn’t altered
what is a disturbance
a relatively discrete event in time that causes abrupt change in ecosystem
how can a disturbance be described
size, time, severity, dispersion
what is succession
pattern of change expected in a community over time after a disturbance
what is primary succession
sequence of change after a catastrophic event
what is secondary succession
sequence of change after a smaller disturbance
what is chronosequence
series of current communities of known age that reflect succession
what is a sere
unit of succession
what is a seral stage
distinct communities within a sere
what is a pioneer community
initial seral stage
what is a climax community
final seral stage
what were the early views of succession
clements: saw succession as a predictable and orderly progression from bare state to climax community
Gleason: saw succession as a continuous process with no end point
what does chronosequence suggest about predictability of succession
predictable and linear
but experiements are on small scale
why are climax states rare
succession is slow
further disturbances reset it
what is the relay floristic model
deterministic changes from pioneer to climax community
groups of species successively appear and disappear from site
will slowly make conditions less favourable for themselves, but more suitable for another species
what in the initial floristic model
all species are present in the begining, and species assume dominance over time
what are camel and slayter’s 3 mechanisms for succession
facilitation : early successional species modify environment to make it more conducive for more species
tolerance: any species that arrives can establish, but r-selected species are eventually outcompeted by k-select species
inhibition: early species inhibit and slow down establishment of later species, slowing succession
what is a r-select species
small investment in offspring, but many
less competitive, but need less resources to reproduce
high mortality rate
what is an k-select species
heavy investment in each offering, few offspring
more competitive , live longer
what does the competitive stress ruderal triangular model (CSR) predict
disturbance creates empty space that initially favours ruderal species
fast growth/dispersal and early rates of maturity
mid seral stage has less empty space and favours more competitive species
late seral stage has fewer resources and favours stress tolerant species
what is the life history strategy model of succession
emphasized adaptations to disturbance (promote dispersal) and adaptations to competition (growth rate)
similar to CSR but less abstract
what is the resource ratio hypothesis for plant succession
alternative to CSR
based on ability of plants to extract resources
succession was considered to be outcome of colonization - competition trade off
what does seed arrival have a big role in
primary succession
what does seed bank have a large role in
secondary succession
what environments are chance events and facilitation most important
severe environments
what environment is competition more important
favourable environments
when in succession is fast growth rate most important
early on
when in succession is longevity important
later stages
when is mammalian herbivory more important in succession
early
when in succession is insect herbivory most important
later in succession
what is a regional species pool
all species that could possibly colonize a community
what is a local species pool
species present in a local community
what are assembly rules
rules that specify why only a limited subset of species of the regional pool is in the local pool
what is a guild
a group of species that exploit the same class of resources in a similar way
what are diamonds assembly rules
1- forbidden species combinations
2- resource availability can alter which species can coexist
what is hutchinsonian ratios
there are limits to similarity
reduced niche overlap reduces competition and allows species to coexist
what did McCloskey believe about observed and imaginary communities
when you have an open system it is untstable so you wouldn’t observe it in nature (imaginary), since another species would come in and filled the gap, thus stabilizing the community making into an observed community which would use more resources (more individuals )
what is Fox’s favoured states model
favoured: if resources to different guilds are approximately equal if all guilds have equal representation
unflavoured: if some guilds are over represented
what are the community assembly filters
dispersal: may limit which species reach a local community
environmental effects: determine what traits are adaptive
biotic filters: such as competition, predation, disease, etc…
when are chance events most important in community assembly
most important when the species pool is large, dispersal is low, primary productivity is high, and disturbance is low
what is species sorting
emphasizes differences in species ability to utilize different patches (species differ in fitness in different environment)
dispersal has no effect on outcome of species interactions
what are mass effects
considers that species differ in niches, but emphasizes role of dispersal
dispersal effects are assumed to be high and with significant effects on population dynamics and species diversity
how does amount of dispersal affect diversities
- alpha : initially increases as less competitive species are saved as less fit (to particular environment) immigrate
- beta: declines with increased dispersal since communities are becoming more similar
what do the overall theories suggest about recovery
- degraded community may be stable and resist recovery
- natural processes may not lead to recovery
- if the abiotic environment is completely restored, the restored community may not be a complete carbon copy of original
how does predator diversity with omnivory and intraguild predation effect strength of cascade
predator diversity with omnivory and intraguild predation reduces strength of cascade
how does predation on mutualists affect the effects of predators on plants via herbivores
predation on mutualists can counter positive indirect effects of predators on plants via herbivores
