February 18, 2011
Ontogeny: readings in Genetics and Physiology/Ability
Dispersal definitions contributed: see online syllabus for others
Matt: I am interested in: Movement in space by individuals or propagules.
Consider example:
Some silly chipmunks in the Sierra. Imagine you have each one radiotagged within a
pretty large area of continuous habitat, and you observe movement at roughly four
scales... (1) most individuals move within a short radius around their dens; constant
movement within this area. (2) occasionally an individual is seen to move on a wider
trajectory, apparently crossing into the "home ranges" (if they are that) of other
individuals, but returning to the area in #1. (3) even less frequently an individual moves
to a peripheral area and starts activities like those in #1. (4) even less frequently (it
happens once during your study) an individual takes off over the pass and is not heard
from again.
So, the question: what explains movement at these different scales. Hypotheses:
#1 is foraging for food
#2 is stealing other individuals' food or looking for mates (not sure)
#3 is a juvenile looking for a place to set up shop
#4 who knows... maybe that individual is responding to packed conditions.... maybe that
individual has a gene that says get the crap out of town and found a new colony....
Personally, I don't see anything to be gained by saying some of those are "dispersal" and
some are not. They are patterns of movement in space, and we can ask questions about
each one. Someone might be tempted to call only #4 dispersal, but beware that the
distinction between #3 and #4 might be pretty fuzzy....
Josh: A non-directed diffusion of genes resulting in ecological or evolutionarily
significant impacts.
Some disagreement in the purpose/meaning for the use of “diffusion.”
Mandy: movement from one population to another
JS: movement to or expansion of home ranges (individual/population/genes)
CS: movement (individual) with potential for contribution to new/different gene pools
NS: Movement of an individual away from an existing pop or away from a parent
organism in which consequences affect species distribution, pop dynamics, pop genetics,
or individual fitness.
KB: Definition needs to consider ecological resources of an area. So, movement
(individual) that utilizes ecological resources
AL: Permanent movement from the natal area for the purpose of reproduction/breeding.
Successful movement passive or active (plants/animals) beyond 95% resulting in a shift
in own home range, natal/parental home range, seed shadow, etc.
CM: Consider differences in ecological and genetic dispersal. There are two types of
dispersal: ecological and genetic dispersal. Genetic dispersal is always ecological
dispersal, but ecological dispersal is not always genetic dispersal. See online syllabus for
details.
What do these have in common? Should we make different definitions for plants and
animals? What are the most important aspects of these definitions?
CS: Movement related to fitness? May not always be dispersal. An animal may
have similar fitness whether they remained in the natal site or dispersed a large
distance.
SB: Consider POTENTIAL for larger fitness benefits.
Nick: Potential for genetic change whether actually results in genetic change.
Can movement be temporal, or is this specifically physical space?
Foraging not dispersal.
Need to define “population” in order to consider movements for breeding/reproduction.
What is local? Can there be dispersal in highly continuous/large populations?
Distinguish dispersal and migration. Consider permanence?
Breeding together despite movementmigration.
Disruption or change in breeding/reproduction/new gene poolsdispersal.
What if you have migratory and non-migratory individuals?
Gene flow and reproduction
Combine definitions to consider genetic and ecological population interactions.
Permanent movement from the natal area for the purpose of
reproduction/breeding given specific genetic and/or ecological interactions. These
interactions need to be specified and considered.
In order for dispersal to evolve there must be higher likelihood of fitness than nondispersal for that individual with those genes and interactions.
Define residents and migrants?
Population definition important.
Migrating pops, nomadic pops, discrete or continuous pops…
Effective breeding size important?
Do genes always need to be successfully transferred? Animals still dispersed, they have
impacts on the new residence/home range as well as impacts on the locale they left.
Dispersal can have altruistic impacts on the original population/group.
Impacts on local/original pop/group…
DispersalSpecialized Functional Movement
May be genetic exchange.
May be a POTENTIAL for genetic exchange.
May include higher fitness POTENTIAL.
Successful reproduction may or may not be a consequence?
Have the option to Not disperse?
Josh’s new definition: Movement of genes resulting in significant evolutionary or
ecological impacts.
Kevin and Nick want to keep “POTENTIAL” to create evo and eco impacts.
Dispersal has costsBody condition, predation risks, lifetime fecundity, etc.
We are trying to make a basis of dispersal definition. More specifications must be
included in the specific system of interest. Likely affected by the kinds of questions you
are asking.
Niche expansion or change. Consider range on a mountain, it can change with
temp/precip. Is this movement of the species dispersal? It affects the entire population, so
it seems like equal opportunity for all to movenot quite dispersal. Might dispersers be
more likely to adapt? Would that make it dispersal or is it niche expansion and so more of
an adaptation?
Pops within patchesmovement after resources? Wouldn’t ideal free distribution
account for interplay and not necessarily be dispersal?
Our amendment to Matt’s definition: give the movement scenario a qualifying scale.
PAPERS:
How does the arms race affect dispersal rates/evolution?
Predator dispersal may promote prey dispersal?
Transmittance analog for dispersal? Parasite/Parasitoid/Host or is this
evolution/speciation/adapting?
Dispersal: issue of Space or Time. Basic understanding is better from the perspective of
space. Movement adaptation across time is a resource change. This is a different basis;
important consideration, but may not provide the best understanding or be the best to
answer certain basic questions.
Example: cicadas using time to prevent other organisms from adapting to their
emergence. Do they display lower rates/frequencies/distances of dispersal because
they use time as the avoidance strategy? Would they evolve increased dispersal
ability if they had a more regular emergence schedule?