Transcript Limiting Resources - Marine Discovery at the University of Arizona

Chapter 3: Ecological and
Evolutionary Principles of
Populations and
communities
Construction of a Population
change Model
dN/dT = f (N,M,R,I,E)
N = population size
M = mortality
R = reproduction
I = immigration (larval settlement)
E = emigration
M is a function of physical environment, competition, predation, etc.
R function of physical environment, resources (e.g., food)
Marine Populations are dynamic, and change is the rule.
 The most important parameters change based on the
life history of the organism that you are trying to model.
• For sessile organisms (like barnacles) the most
important parameters are: N, I, M
•For mobile populations with large home ranges E,
emigration is also important
•For animals that are widely dispersed (deep sea
animals): R becomes the most important factor, along
with N and M.
Example of Population Model
Barnacles: What parameters matter the most?
dN/dT = f (N, I, M)
I is larval settlement
M a function of larval-adult interactions, overgrowth, predation.
Note R doesn't matter if planktonic larvae mainly go elsewhere
(are dispersed)
Survivors
Survivorship curve
Planktonic
larval
stage
Post-settling stage
Mortality pattern expected for a species with a
planktonic larva. Note higher mortality rate of
larval stage.
Modes of Population Change
Exponential
Growth
Logistic growth
Random change
Limiting Resources (Carrying capacity K)
•Space is a limiting resource to these
colonies of colonial ascidians
•For marine populations space and food are
the most common limiting resources
Metapopulation dynamics
Metapopulations are a series of interconnected
sub populations, some of which may contribute
disproportionately large numbers of individuals to
the metapopulation as a whole
Are extremely important in marine populations
because of the life histories of many marine animals
(larval dispersal).
Examples where metapopulation dynamics are
important include a large barrier reef with nearby
smaller reefs; an organism with a widely dispersing
larval stage.
Metapopulation
• Definition: A group of interconnected
subpopulations among which there is movement
of individuals
• Some subpopulations are sources of individuals
that move to other subpopulations
• Other subpopulations are sinks, which means
that they may receive individuals from other
subpopulations, but they are not sources
(example, only juveniles disperse, but the
subpopulation in question does not have
individuals that reproduce successfully)
Metapopulation - interconnected group of
subpopulations
Example: Intertidal
arboreal snail, Littoraria
filosa, occurs commonly
on mangrove leaves in
Queensland, Australia.
Snails have planktonic
larvae that are in the
water for a month.
• In forests, snails appeared to be annuals that died every year.
•On isolated trees, snails did not die
•Predatory fly lives in forest and many of the snails in the forest
don’t survive to reproduce.
Spatial Variation of Populations
Spatial distribution is a measure of spacing among individuals
of a given area.
 Scientists frequently study the spatial distrubution of
organisms along with determining the density of organisms in a
given area.
Knowing the distrubution and density can the lead to
interesting hypothesis about the environmental factors that are
impacting the population.
Example: barnacles
Spatial Distribution of Individuals
Random
Uniform
Aggregated
Ecological Processes at the
community level
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Competition
Predation
Disturbance
Parasitism
Larval Dispersal
Facilitation
COMPETITION
LIMITING RESOURCES
(1) Renewable - e.g., copepods exploiting diatom
population
(2) Non-renewable - space on a rock exploited by
long-lived sessile species
Outcomes of Competition
COMPETITIVE DISPLACEMENT - one species
outcompetes another for a resource
COEXISTENCE - two species exploit different
resources, some process allows two species to
exploit same resource without
displacement
Intermediate DisturbancePredation Hypothesis
Low levels of disturbance or predation: Competitive dominant
species takes over
Intermediate levels: Promotes coexistence, more species present
High levels: most individuals removed, reduces total number of
species
SUCCESSION
Predictable order of appearance and dominance of species, usually
following a disturbance.
SOME MODES OF SUCCESSION
(1) Early species modify habitat, which facilitates colonization by later
species
(2) Late species exclude colonization of early species
(3) Early species hold space until death, then are replaced by late species,
which do the same