Chapter 5 Population Ecology

Counting individuals What constitutes an individual organism?

Variations on the individual Unitary organisms - one zygote per embryo produces one organism

Variations on the individual Modular organisms - one zygote per embryo produces one module, which eventually produces more modules like itself Branching or shoot development in plants, budding in Hydra, sponges, fungi

How to count individuals in a population Some organisms - possible to easily count all individuals Others must be subsampled and estimated Plants and some animals - quadrat Soil, water dwellers - volume Animals - mark and recapture

Mark and recapture Random sample Release Try to recapture Theory - marked individuals will remix within population; proportion marked in next sample represents proportion in entire population

Mark and recapture example Population size (N) #marked on Day 1 = Total catch on Day 2 # of recaptures N = (# marked on Day 1) x (Total catch on Day 2) # of recaptures

Gilmore Creek Brown Trout 200 m stream reach=840 m 2 area 4.2 m average stream width Day 1: 169 trout captured, marked, released Day 2: 178 trout captured 80 marked (recaptures), 98 unmarked N = (# marked ) x (total catch Day 2) # of recaptures N = 169 x 178 = 377 trout 377 trout/840 m 2 = trout m 2

Life cycles Patterns of birth, death, growth are dictated by an organism’s life cycle 5 main types of life cycles

Life cycle types Annual Overlapping iteroparity Overlapping semelparity Continuous semelparity Continuous iteroparity

Semelparous Individual organism has single reproductive event during its life, then dies Invests large amount of energy in reproduction

Iteroparous Individual may have many reproductive events during season or life Invests lesser proportion of resources in reproduction

Annuals 12 months or less to complete life cycle Discreet, non-overlapping generations May or may not overwinter as non-seed/egg May be either semelparous or iteroparous Annual may be a misnomer for some plants with seeds that do not always germinate the year after being produced Seeds may lie dormant in seed bank for several years before germinating

Overlapping iteroparity Overlapping generations (yearlings, 2-year- olds, etc.), iteroparous Distinct breeding season Examples: temperate-zone trees, long- lived, seasonally breeding vertebrates (deer, most fish, snakes, birds)

Overlapping semelparity Overlapping generations (several age classes present [at least biennial]), semelparous New offspring in population every year (distinct breeding season) Require 2 or more years to mature and reproduce, then die Most common in plants, also in some species of octopus, salmon

Continuous semelparity No distinct breeding season because of favorable environmental conditions Many overlapping ages continually growing, reproducing, dying Example: some animals in tropical oceans

Continuous iteroparity No distinct breeding season Many overlapping ages Example: humans

Life tables Used to follow changes in births, deaths, growth of population through time Of differing complexity and usefulness depending on life cycle of organism being examined Easiest for annuals, more difficult for other types

Life table variables xlife stage or age class a x total number of individuals observed at each stage or class l x proportion of original number of individuals surviving to the next stage or class; survivorship d x proportion of original number of individuals dying during each stage or class; mortality q x mortality rate for each stage or class k x "killing power;" F x total fecundity, or reproductive output of entire population, for each stage or class m x individual fecundity, or mean reproductive output, for each stage or class l x m x number of offspring produced per original individual during each stage or class; product of survival and reproduction R 0 basic reproductive rate

Cohort life table Group of individuals “born” within same short time interval is followed from birth through death of last survivor

Grasshoppers - a cohort life table

Phlox - a cohort life table

Static life tables Life tables more difficult to construct for longer-lived organisms, and those with many overlapping generations Difficult to follow single cohort throughout entire life (many years) Static life table is produced - snapshot in time

Static life tables Need information on total population size and its age structure at some point in time Can get messy if older age classes have more individuals than younger age classes Different mortality, recruitment May need to smooth data to get things to work

Red deer - a static life table