ws 06/07 ralf schulz - campus landau · ralf schulz. lecture content • introduction overview...

Stress Ecology

WS 06/07

Ralf Schulz

Lecture content

• IntroductionOverview Definition of stress (ecology)

• Factors and resources (and associated reactions)Factors Resources

• More complex reactionsLife cycle strategies (Ecological traits)Predation and disturbance in communitiesAbundance (and ist variation)Anthropogenic impact on abundance (harvesting and killing)

• Seminar on stress ecology

Complex reactions

Life cycles

What is a population?

Complex reactions - Life cycles

Group of individuals of a studied species

- belonging to the same taxonomic unit- occuring in the same location- occuring together at the same time

Population size and population area


Space in which the individuals of a population are distributed

Number of individuals making up a population

Population density


Number of individuals (animals) or units (plants) per unit of area

ABCDEFGHIJ

1 2 3 4 5 6 7 8 9 10

0

1 - 4

5 - 9

10 - 14

15 and more

Polygonum viviparum: local variability in population density due to patchy distribution

Changes within populations


- Birth- Death- Migration

What is an individual?


A structural, functional and genetic unit

Most animals, but not many plants

Individuals - Problems with plants


1. Development from modules, clonal structures2. Asexual seed development3. Identical twins4. „in vitro“ reproduction, e.g. oil palm trees5. „Genet“ not applicable

Unitary and modular organisms


Unitaryorganisms

Morphological form is more or less defined and final form already developed in the embryonic stage, only little changes in forms in the adult stage (apart from size):e.g. insects, mammals, humans.

Modularorganisms

Neither temporal sequence nor form fully predicatable (depends on environmental factors), organisms consists of modules (leaf pluspetiole or blossoms), often branched and sessile (adult stages):e.g. almost all plants, sponges, corals, many fungus.

Modular organisms: Some examples

Complex reactions - Life cycles Begon et al 1998

Lemna Hydra

Trifolium Hydrozoa

Buchloe Hydrozoa

Festuca Bryozoa

Oak Corals

Populations are influenced by:


Location, Death, Migration

In order to estimate populations size, measurements or countings are required

Possibilities for countings


- Killing of a population (e.g. fish farm)

- Life-capturing of all individuals of a population (e.g. ringing of birds)

- Mark-recapture

- Estimations from representive subsamples (e.g. per squaremeter)

Some problems with countings


Modulary organismsExample: When is a tree a tree (seed, germ, joung tree)?

How to count birth events correctly?Example: How many embryos die before birth?

How to count birth events correctly?Example: Herbivory on seeds or germ

Life cycles


Life cycle strategy (life history):

Birth

Growth phase

Reproductive phase

Postreproductive phase

Death

Prerequisite:Knoweldge of the main stages in the life of an organism

Unitary organisms: schematic life cycle


But:


- Several or many generations occur throughout the year

- Only one generation at all (annual)

- Life cycle covers several years (perennal)

- Growth period prior to reproduction requires resources

Annual life cycle: Chorthippus brunneus (grass hopper)


1947

1948

11

0

7.3

0.079

Gebu

rt

Über

leben

0. 72

0. 76

0. 76

0.89

Eigelege18.25

Eier200.75

Larven I15.86

Larven II15.86

Larven III15.86

Larven IV15.86

AdulteWeibl. 2.5, Männl. 2.8

AdulteWeibl. 2.9, Männl. 2.9

Semelparity and iteroparity


Semelparity IteroparityRepeated reproduction, part of the energy used for own survival

e.g. humans, mammals, trees

One reporductive phase, followed by death

e.g. biannual plants or long-living plants, such as Agaves, resources ± fully allocated to reproduction: pacific salmon

Longer life cycles


Life and fertility tables....


Cohort life tableEstimates for a certain time period the survival of the cohort members of a population

Static life tableNumber of survivors in different age classes for a certain period oftime

Age-specific fertility tablesNumber of individuals in different age classes, contributing to the fertility

… aim to quantify birth and death.

Annual life table


Life table of cohorts

Most reliable method to estimate the age-specific death and fertility in a population.

Cohort =

Group of individuals, born during a certain time period

Example:Poa annua - Einjähriges Rispengras,

Poaceae, after Lowe (1975)

Cohort life table (Poa annua) after Lowe 1975


Durch-schnittli-che Anzahl Samen pro Indivi-duum mit dem Alter x

log10ax –log10ax+1

Kx =killingintensity

Stadium-spezi-fischeMortali-tätsrate

Standar-disierte Anzahl gestorbe-ner Pflanzen zwischen x und x+1

Standar-disierte Anzahl lebender Pflanzen zu Be-ginn je-der Peri-ode

Anzahl lebender Pflanzen zu jeder Periode

Alter (in Viertel-jahres-perioden)

0300620430210603010-

0.0670.1370.2220.3420.4260.5560.699

3.0002.9332.7962.5742.2321.8061.2500.551

2.9262.8592.7222.5002.1581.7321.1760.477

0.1430.2710.4000.5440.6260.7220.8001.000

14323225020410746.214.243.56-

10008576253751716417.83.560

843722527316144541530

012345678

Bxkxlog10lx

log10ax

qxdxlxaxx

Age-dependent fertility of Poa annua


Survival and death rate of Poa annua


Life cycles and resources


Every life cycle has only a limited amount of resources available

- Allocation to different life phases (e.g. growth, reproduction)

- Temporal changes in life phases (e.g. early start of fertility)

Life history strategies


r-selected organisms spent most of their life in the exponential growth phase

r-selecting habitats Habitate (e.g. open pioneer areas)

N K

r A

B

dNdt

1N

x

Idealised linear decrease of the netto growth rate per individual with increasing population size (N);r = specific natural growth rate



K-selected organisms spent most of their life in the K-dominated phase (intensive competition) of the population growth

K-selecting habitats e.g. dense populations with restricted resource availability (meadows)

[K = derived from capacity]



r-selectingExample: pioneer area

K-selectingExample: meadows



r-strategy

many small

offspring

K-strategy

few large

offspring

See you next week!

ws 06/07 ralf schulz - campus landau · ralf schulz. lecture content • introduction overview...

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