Population Ecology (W7 L4) Flashcards
Dispersal?
= movement of individual animals from place to birth to where it reproduces.
Dispersal attributes? (2)
• Based on an individual’s decision about where to occur on the landscape.
• Can also apply to seeds from plants & spores from fungi.
Dispersion & Distribution is based on?
Based on several individuals in a population.
Dispersal is based on?
Based on an individual’s decision about where to occur on the landscape.
Migration?
= movement back & forth between seasonal home ranges.
Local movement?
= fine-scale movement within home ranges.
Immigration/Emigration?
= movement into or out of a study area of arbitrary size or delineation (movement into or out of a population).
Dispersion?
= the spatial pattern of locations demonstrated by individuals (eg, animals, plants, fungi, bacteria) in an area.
Dispersion attributes? (2)
• Based on several individuals in a populations.
• Population level outcome of dispersal.
Distribution?
= the area occupied by a population or species depicted as a line drawn around a dispersion.
Forms of movement? (2)
● The minimum distance needed to reach the nearest unoccupied habitat.
● The longer distances, crossing suitable areas before settling in an ideal/optimal habitat.
Minimum distance needed to reach the nearest unoccupied habitat?
= animals wander around until they find places that are good enough.
Suitable areas in longer distances…?
= good enough areas.
Why is the 2nd form of movement a risky strategy?
Forms of mechanisms? (2)
● Young are pushed by parents out of the natural home range.
● There is a genetic or physiological prompt to move away from natal areas.
Explain 1st form of mechanism?
When mothers are planning to have more children & need space to keep those future young.
Egs of 1st form of mechanism? (2)
• Birds.
• Mammals (Rhino).
Eg of 2nd form of mechanism?
Salmon.
Forms of dispersal? (2)
• Pre-saturation.
• Saturation.
Pre-saturation dispersal?
= young leave the natal home range even if the population is in low abundance.
Saturation dispersal?
= young animals leave when the population reaches the threshold density determined by food availability/food limitation.
Pre-saturation dispersal attributes? (2)
• Common in small mammals.
• Happens before the population is saturated & full of competition.
When does Pre-saturation dispersal happen? (2)
Before population is saturated & full of competition.
Benefits of Pre-saturation dispersal? (2)
• Avoids inbreeding.
• Avoids competition for mates.
Saturation dispersal attributes? (2)
• Common in large mammals.
• Leave only when they suffer the effects of high competition (less resources).
When does Saturation dispersal happen?
When competition is high (less resources).
Eg of Pre-saturation dispersal?
Lemmings.
Egs of Saturation dispersal? (2)
• Carnivores.
• Herbivores.
Role of mating systems?
= play a role in how animals disperse from the natal home range.
Role of mating systems involves…?
The General rule.
The General Rule?
= males compete for reproductive opportunities, females are concerned with getting enough resources to support their reproductive efforts.
Importance of the General rule?
Determines whether males tend to disperse or whether females tend to disperse.
In promiscuous/polygynous species attributes? (2)
• Males tend to disperse more & more away from the natal home range as a strategy to find mates.
• Females remain in the natal home range (philopatric).
Egs of promiscuous/polygynous species? (2)
• Kudu.
• Nyala.
In monogamous species attribute?
Both males & females tend to disperse from natal home range (as they leave as a pair).
Egs of monogamous species? (2)
• Hadeda ibis.
• Wolves.
In higher vertebrates attributes? (4)
• Refers to birds & mammals.
• One sex tends to disperse more than the other.
• In mammals, it’s males.
• In birds, it’s females.
Why is it that in mammals, under higher vertebrates, males are the ones to disperse?
It’s because females commit to offspring growth.
Why is it that in birds, under higher vertebrates, females are the ones to disperse?
It’s because males defend nesting sites.
Categories under the General rule? (3)
• In promiscuous/polygynous species.
• In monogamous species.
• In higher vertebrates.
Factors driving dispersal? (3)
• Effort to reduce competition for mates.
• Effort to avoid inbreeding.
• Way to reduce competition for food/habitat resources.
Explain eg of polygynous species? (2)
● Females tend to invest more in offspring than males therefore, whether they disperse or not depends on their ability to find adequate resources.
● Males are focused on finding mates therefore, whether they disperse or not depends on their ability to find mates.
Inbreeding avoidance attributes? (3)
• Commonly cited idea.
• Isn’t clearly demonstrated.
• Depends on the species.
Dispersers attribute/con/disadvantage of being a disperser?
Have lower survival.
Why do dispersers have lower survival? (2)
Young animals with little experience moving through unfamiliar areas ¹don’t know where good food resources are & ²don’t know where protection from predators is.
Egs of Dispersers? (2)
• Egyptian geese.
• Costs vs benefits of young oribi that would rather stay with their father to help defend his territory.
Types of dispersion patterns? (3)
• Random.
• Clumped.
• Regularly spaced.
Random pattern of Dispersion attribute?
No order to distribution/dispersion whatsoever.
Eg of Random dispersion pattern?
Morula trees.
Clumped dispersion pattern attributes? (2)
• Most common.
• Is the outcome of selection of ¹patchy resources, ²habitat, social groupings or ³anti-predator strategies.
Clumped dispersion pattern is an outcome of the selection of what? (3)
• Patchy resources.
• Habitat, social groupings.
• Anti-predator strategies.
Egs of Clumped dispersion pattern? (2)
• Elephants.
• Wildebeest.
- Herding animals.
Eg of Regularly spaced dispersion pattern?
Leopards.
- Individuals.
Ways to assess dispersion? (2)
• Grid cells.
• Nearest Neighbour Distance (NND).
Grid cells attributes? (2)
• Put a grid over the study area.
• Within each cell, calculate ¹a mean number of points in each cell (x) & a ²standard deviation (sd).
Problem with Grid cells method of assessing dispersion?
Conclusion depends on the size of the grid cell.
Large grid cells attributes? (2)
• More cells with similar counts.
• More likely to conclude random dispersion but it might not be.
Small grid cells attributes? (3)
• More cells with zero.
• Larger differences between cells.
• More likely to conclude Clumped dispersion even if it might not be.
sd/x values for Grid cells? (3)
• sd/x ~ 1.
• sd/x > 1.
• sd/x < 1.
sd ~ 1?
Dispersion is random.
sd/x > 1?
Dispersion is clumped.
sd/x < 1?
Dispersion is regular.
