Plant Ecology - Chapter 5

Populations

Population Growth

BirthsDeathsImmigrationEmigration

Population Growth

Genets - genetically distinct individualsRamets - physiologically independent but not genetically distinct individuals

Population Growth

“Birth” - seed production, vegetative clones, mature pollen grains (gametophyte)?

Population Growth

“Individual” - distinctly separate plants (unitary) or interconnected, related individuals (modular)

Population Structure

Population size important, but so is the distribution of individuals among different ages/sizes/stagesHave differing importance to population

Population Structure

Animal populations usually age-structuredAge determines role, importance to populationAge not as important for plants - size is far more importantPlant populations stage-structured

Population Structure

Plant stages frequently based on size - number of leaves, mass, height categories, diameter categoriesFrequently impossible to determine plant age

Population Structure

Plants have very flexible growth patternsCan lose parts and shrink from year to year, go through years of dormancy, or not appear above ground in a given year

Population Structure

Stage structuring difficult under these circumstancesPlants can advance directly through stages, remain at some stage, or undergo reversions

Population Structure

Plant ecologists must keep track of multiple stages and all possible transitions between them

Population Structure

In structured populations, individuals of different stages make different contributions to future population growthPre-repro, repro, post-repro

Life Cycle Graphs

Summaries of transitionsbetween stages

Life Tables - Cohort

Matrix ModelsCombine life cycle graphs with life table datato understand which stage classes have thestrongest effects on population growth

Which stage needs protection? Which stageclass is most affected by fire? Which stagelimits population growth?

Matrix ModelsCan be used to predict age-based quantities fromstage-based data

Long-Lived Plants

Problems studying long-lived plantsLonger life span than researchers!Year-to-year variation in environmental conditions, longer intervals between censuses - misses younger plants

Long-Lived Plants

Static life tables problematic - assumptions such as stable age structure impossible to justifyIncorporate cyclic variability (e.g., pest outbreaks)Compare old to new photographs

Variable Population Growth

Matrix modeling generalizations allow for estimates not possible two decades agoLong-run population growth ratesExtinction probabilitiesMinimum viable population sizes