Plant Ecology Chapter 5 Populations Population Growth Births

Plant Ecology - Chapter 5 Populations

Population Growth Births Deaths Immigration Emigration

Population Growth Genets - genetically distinct individuals Ramets 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/stages Have differing importance to population

Population Structure Animal populations usually age-structured Age determines role, importance to population Age not as important for plants - size is far more important Plant populations stagestructured

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

Population Structure Plants have very flexible growth patterns Can 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 circumstances Plants 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 growth Pre-repro, postrepro

Life Cycle Graphs Summaries of transitions between stages

Life Tables - Cohort

Matrix Models Combine life cycle graphs with life table data to understand which stage classes have the strongest effects on population growth Which stage needs protection? Which stage class is most affected by fire? Which stage limits population growth?

Matrix Models Can be used to predict age-based quantities from stage-based data

Long-Lived Plants Problems studying longlived plants Longer 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 justify Incorporate cyclic variability (e. g. , pest outbreaks) Compare old to new photographs

Variable Population Growth Matrix modeling generalizations allow for estimates not possible two decades ago Long-run population growth rates Extinction probabilities Minimum viable population sizes