Ecology 3 Flashcards
Description of equilibria models
1) Competition based
2) Assume that community composition represents the stable outcomes of interspecific interactions
3) Assume that the community will return to an equilibrium after perturbations
4) Diversity is attained because more species are able to coexist in a stable equilibrium
5) Stable dynamics include stable equilibria, stable limit cycles, and chaos
5) Involve settlement and post-settlement processes
6) Stress biotic interactions
Morin p. 284
Description of non-equilibria models
1) Non-equilibrium mechanisms generally prevent an equilibrium from being reached, and therefore prevent exclusions of species that might result as a consequences of that equilibrium
Morin p. 284
Debate between equilibria and non-equilibria models
1) It is unclear if natural communities are at equilibrium or far from it
2) Evidence needed to assess stable equilibrium behavior is difficult to obtain (need to perturb system and need to monitor for a long time)
Morin p. 284
List of equilibria models
1) Compensatory Mortality
2) Niche Diversification
3) Predation Hypotheses
4) Intransitive Networks
Morin p. 293-294
List of non-equilibria models
1) Gradual change hypothesis/Storage Effect/Lottery Model
2) Lottery hypothesis
3) Intermediate Disturbance Hypothesis
4) Non-equilibrium predator-mediated coexistence
Morin p. 295-296
Compensatory Mortality Assumptions
1) Competition-based (resources are limiting)
2) Disturbance removes most abundant species (frequency-dependent mortality)
3) Perturbation does not alter resource availability
Compensatory Mortality Predictions
1) Inverse relationships in species abundances
2) Most abundant species at any time suffers disproportionate absolute mortality
(same as Predation hypotheses)
Compensatory Mortality Example
1) Branching corals are heavily impacted by disturbance (hurricane)
2) In areas where branching corals have been eliminated due to disturbance there is high diversity
Niche Diversification Assumptions
1) Competition-based (resources are limiting)
2) Resource partitioning (each species is superior competitor for particular resource or niche)
3) Perturbation does not alter resource availability
Niche Diversification Predictions
1) Total number of individuals and number of species limited by resources (assemblage wide carrying capacity)
2) Relative abundance of species determined by number of available niches
3) Predictable composition and relative abundance
Niche Diversification Example
1) Motile animals are more likely to display high degree of specialization than sessile species
2) Galapagos finches
Predation Hypotheses Assumptions
1) Predator causes disproportionately higher absolute mortality in most abundant prey species (competitive dominant)
2) Induces competition or otherwise regulates prey populations
3) Allow persistence of rare species or inferior competitors
Predation Hypotheses Predictions
1) Inverse relationships in species abundances
2) Most abundant species at any time suffers disproportionate
(same as Compensatory mortality)
Predation Hypotheses Example
1) Keystone predation of Pisaster in the rocky intertidal
2) Can include cases of compensatory mortality, predator switching, and keystone predation
Intransitive Networks Assumptions/Predictions/Example
1) Circular competitive hierarchy
2) Connell tested this hypothesis and found no circular pathways
3) Connell asserts that these pathways are likely more present in distantly related species
Gradual Change Hypothesis Assumptions
1) Competition based (resource limitation)
2) Larval pool saturates resource
3) No resource partitioning (equal competitors)
4) Likelihood of creating and acquiring resource due to random chance
5) Likelihood of settlement equals relative abundance in larval pool
(same as Lottery Model)
BUT
1) Relative recruitment success of species changes through time
2) Variable success due to variation in larval production and conditions
3) Species persist through bad recruitment periods and “Store” recruitment events
Lottery Hypothesis Assumptions
1) Competition based (resource limitation)
2) Larval pool saturates resource
3) No resource partitioning (equal competitors)
4) Likelihood of creating and acquiring resource due to random chance
5) Likelihood of settlement equals relative abundance in larval pool
(same as gradual change hypothesis)
Gradual Change Hypothesis Predictions
1) Unpredictable as to what species will recruit to any location or at any time (variable recruitment)
2) Assemblage wide carrying capacity
3) Relative abundance of species fluctuates unpredictably, including after perturbation (variable abundance)
(same at Lottery Model)
Lottery Hypothesis Predictions
1) Unpredictable as to what species will recruit to any location or at any time (variable recruitment)
2) Assemblage wide carrying capacity
3) Relative abundance of species fluctuates unpredictably, including after perturbation (variable abundance)
(same as Gradual Change Hypothesis)
Gradual Change Hypothesis Example
Paradox of the plankton
Lottery Hypothesis Example
1) Certain guilds of coral reef fish may fit this hypothesis
2) Recruitment to new sites is likely independent of the stock of eggs released as plankton (independent recruitment)
3) Juveniles grow quickly after they colonize to vacant places, and thus are able to hold their territory against further invasion by smaller juveniles of any species from the plankton (juveniles outcompete)
Pluralistic Approach Assumptions
1) Combination of many models
2) Each model has varying importance over time
3) Orthogonal manipulations of competition, predation, and disturbance
Pluralistic Approach Predictions
1) Relative importance of any model is determined by whether recruitment is modified by post-recruitment processes
Pluralistic Approach scehmatic
1) If Post-recruitment competition is intense:
a) If recruitment is modified by post-settlement processes: Niche Diversification
b) If recruitment is NOT modified by post-settlement processes: Predation/Disturbance models
2) If Post-recruitment competition is weak:
a) If recruitment is modified by post-settlement processes: Recruitment Limitation
b) If recruitment is NOT modified by post-settlement processes: Lottery Hypothesis
Intermediate Disturbance Hypothesis Example
1) Sousa’s boulders
2) early succession: Ulva
3) mid succession: Gelidium, Chondracanthus, Gigartina leptorhynchus
4) Late succession: Gigartina canaliculata
Intermediate disturbance hypothesis models
1) Facilitation: early colonizers ameliorate the habitat for later colonizers
2) Inhibition: early colonizers make the habitat worse for late successional species, but late successional species grow up and juveniles out compete early colonizers
3) Tolerance: early colonizers make the habitat worse for late successional species, but late successional species tolerate early colonizers and eventually outcompete them
Intermediate disturbance hypothesis Assumptions
1) Species diversity is reduced by competition
2) a trade-off exists between ability to tolerate disturbance and competitive ability
3) a trade-off exists between colonizing ability and competitive ability
4) Successional seres have at least two stages
5) regional species pool is much larger than the number of species that can occur in a small patch
Collins and Glenn (https://newzealandecology.org/nzje/2018.pdf)
Intermediate disturbance hypothesis predicts
1) Intermediate disturbance yields highest diversity
2) When disturbance is too high, only a few species can persist
3) When disturbance is too low, many species can invade and predation and/or competitive exclusion can occur
Recruitment Limitation Hypothesis Assumptions
1) High mortality of pelagic larvae limits new recruits (recruitment is limited)
2) Larval supply limits recruitment below what is required to saturate resources (no resource saturation)
3) No competition
4) Mortality is density-independent
Recruitment Limitation Hypothesis Predictions
1) Total numbers and relative abundance fluctuates with variable larval supply
Recruitment Limitation Facts
1) Recruitment limitation means that post-settlement processes are density-independent (but this is only maintained to a certain point)
2) generations are independent of one another (i.e. number of individuals in one generation do not influence future recruitment)
3) When larval supply is low, predation is unimportant
Succession
1) Process of temporal change in community composition following disturbance
2) Three mechanisms: facilitation, inhibition, and tolerance
History of the study of succession
1) Plant ecologists identified striking temporal changes in species composition
2) These studies identified sequence of species replacements until system reaches an established state without further changes
3) Competition was regarded as the most important biotic interaction in these early views
Who was the first to study succession?
1) Succession was first studied by Henry Cowles
2) He used differences in vegetation occurring on sand dunes of different age to infer successional patterns
3) Moving inland from the lake margin, dunes increase in age and differ in species composition
Clements view on succession
1) Clements promoted the idea that ecological communities were analogous to super organisms, with different species interacting in mutually supportive ways to promote community development
2) Clements believed that successional stages, called seres, reached an endpoint, called the climax
3) Clements argued that differences in climax communities were the result of different environmental regimes and failure to reach these climaxes was due to high disturbance
Clements Gleason debate
1) Clements: concerned with whether communities developed as tightly integrated sets of species with some species selflessly paving the way for others
2) Gleason: Species increase or decrease independently of one another through successional time, an individualistic view of succession
3) Gleason: Community is nothing more than the collection of species who individual physiological requirements allow them to exploit a particular location
Facilitation model
1) Disturbance occurs
2) Of the species that arrive in the open space, only certain “early succession” species can establish themselves
3) Early occupants modify the environment so that it becomes less suitable for subsequent recruitment of “early successional” species but more suitable for recruitment of “late succession species”
4) The growth to maturity of later succession species is facilitated by environmental modification by early successional species and earlier species are eliminated
5) Sequence continues until resident species no longer facilitate the invasion of other species
6) Further recruitment or colonization can only occur if a resident is damaged or killed.
Tolerance model
1) Disturbance occurs
2) Of the species that arrive in the open space, any that are able to survive as adults can establish
3) Early occupants modify the environment so that it becomes less suitable for early successional species, but this modification has little or no effect on the establishment of late successional species.
4) Juveniles of late succession species that invade or are already present grow to maturity despite the continued presence of healthy individuals of early successional species. Over time, earlier species are eliminated.
5) Sequence continues until no species exists that can invade and grow in the presence of residents
6) Further recruitment or colonization can only occur if a resident is damaged or killed.
Inhibition model
1) Disturbance occurs
2) Of the species that arrive in the open space, any that are able to survive as adults can establish
3) Early occupants modify the environment so it becomes less suitable for subsequent recruitment of both early and late succession species
4) As long as individuals of earlier colonists persist undamaged and/or continue to regenerate vegetatively, the exclude or suppress subsequent colonists of all species
5) Further recruitment or colonization can only occur if a resident is damaged or killed.
Example of facilitation model of succession
1) Cowle’s sand dunes
2) colonization by “pioneer” species, e.g. soils newly exposed by retreating glaciers ameliorate these conditions by reducing pH, increasing nitrogen content, and adding a layer of organic soil over the hardpan, reducing desiccating winds. Following this habitat amelioration seedlings of spruce trees then appear.
Example of tolerance model of succession
1) There are currently no adequate examples of this model
2) In order to support this successional model, observations demonstrating that invasion and growth to maturity of later species neither requires conditions produced by earlier species (which would prove model 1) nor are inhibited by them (which would prove model 3).
Example of inhibition model of succession
1) Observations that early species suppress the establishment of later ones, inhibit their growth, and reduce their survival.
2) Early-colonizing land plants reduce the rates of germination and growth of other species arriving later.
3) A closed canopy of shrubs prevented the invasion of trees for periods up to 45 years
4) Sousa’s boulders, removing early successional algae from boulders increased diversity of later successional species
