2011 Lecture 4a Ecosystem Dynamics I

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Structure &

Diversity(Ecosystem Dynamics I)

NR216 Ecology Lecture

February 1, 2011



What is Ecology?

A science,

± the study of ecosystems,

± that looks at the abundance, dynamics,& distribution of organisms and their

interactions

with their living & non-living

environment«

± with no value judgements.



What is Ecology?

+ society¶s value judgements

about the environment

basis for the development of

successful conservation &

sustainable resource management

= ³Environmental Science´



What is an Ecosystem?

Kimmins, Balancing Act, p.28 :

³The total assemblage of living organisms

along with the non-living environment in a

particular area.´

Biotic factors +

Abiotic factors + Processes.

Look at Biodiversity



5

Biodiversity

³ Variation in the biotic

community«´

³ The diversity of life in all its

forms and all its levels of

organization«´Patrick Moore on Biodiversity



6

Types of Biodiversity

Genetic Diversity (species level)

won¶t discuss in this class much

Biotic Diversity (ecosystem level)

Ecosystem Dynamics I

Temporal Diversity (change over time)

Ecosystem Dynamics II



Assess Ecosystems

1. Structure

2. Function

3. Complexity4. Biotic Diversity

5. Interdependency (at different levels)

6. Tendency to change over time(Ecological Succession)



8

Biotic Diversity

1. Alpha Diversity stand level diversity

local species richness & evenness

2. Beta Diversity diversity across a local

environmental gradient

ie. elevation, moisture3. Gamma Diversity

Landscape level or regional diversity

ie. watershed



1. STRUCTURE

1. Vertical Structure (Alpha diversity)

w ithin an ecosystem

eg. coniferous forest :

overstory (dominant trees)understory (suppressed trees)

woody shrubs

herbs (forbs, graminoids[grasses & sedges], ferns &

fern allies) bryophytes (mosses, lichens,

liverworts & hornworts)

[W e w ill Look at this in Lab this w eek]



1. STRUCTURE

2. Horizontal Structure (Beta Diversity)

bet w een ecosystems

changes along an ecological gradient changes after a disturbance



2. FUNCTIONEcosystems are ´natural biomass factoriesµ

Energy source(solar radiation, stored as chemical energy)

+

Essential nutrients(from atmosphere & soil)

=

Biomass

carbohydrates (sugars, starch, cellulose) proteins

lipids (fats)

nucleic acids



3. COMPLEXITY

Many individual components interact, so

hard to predict future events or

conditions.

Complexity determined by :

± regional climate,

± soil,

± topography &

± the diversity of the local ³biotic community´



4. BIOTIC DIVERSITYE&FB p.388ff

4.1 Species richness :

# of species

4.2 Species evenness :

relative abundance of each species

4.3 Dominant versus Keystone Species

4.4 The concepts of ³niche´



4.1 Species RichnessBiotic Diversity E&FB p.555

~ 1.4 million different species ID¶d & named world-

wide to date

~ distinct geographic patterns of ³species richness´:

from Equator to poles

from low to high elevations in mountains

species as isolation (ie. peninsulas, islands)

# species as topographic diversity (ie. mts.)



4.1 Species RichnessBiotic Diversity E&FB p.555

Why these patterns?

Lots of factors, can¶t quantify exactly why :

o ecosystem productivity

o topographic differences

o stability &/or moderation of climate



4.2 Species Evenness or

CompositionBiotic Diversity

Dominant Species (E&FB p.388)

not necessarily the most important; may be :

most numerous

have largest biomass

take up the most spacemake the largest contribution to energy flow



4.3 Keystone Species

Biotic Diversity

«is the most important species.

?The one whose presence is

critical to the integrity

of the whole community or ecosystem.

examples

bees



4.4 Niche

Biotic Diversity (E&FB pp.257ff)

?

4.4.1 Ecological niche (habitat, role etc.)

4.4.2 Fundamental niche (potential)

4.4.3 Realized niche(actual)

shrimp...



4.4.1 Ecological NicheBiotic Diversity

Broadly Used : Habitat

Functional role

Food habits Morphological traits

Restrict to 1 or 2 dimensions :

eg. ¸ feeding niche¸ space niche

¸ tolerance niche



4.4.2. Fundamental NicheBiotic Diversity

Fundamental role

of an organism in a community IFno competition for space or resources.

³«total range of environmental conditionsunder w hich a species can survive.´

E&FB p. G-7



4.4.3 Realized NicheBiotic Diversity

Conditions

under which organismreally exists.

³«portion of fundamental niche spaceoccupied by a population in face of competition from populations of other

species.´ E&FB p. G-14



BIOLOGICAL DIVERSITY

«is a reflection of the overlap of

niches, with or without

competition.Loss of a keystone species would

lead to radical change in the

structure of an ecosystem ±³collapse´.



5. INTERDEPENDENCY

Interaction of Components of an Ecosystem :

Climate reflected in

vegetation & soils of an area.BUT «

¸ Different soils, different vegetation

¸ Different vegetation, different animals &microbes



5. INTERDEPENDENCY

Disturbance?

¨ in one component ¨ in others

Eg. ¨ in climate (drier, warmer) ¨ in vegetation

¨ in soil (fire = fast decomposition) ¨ in vegetation

¨ in animals (insect cycles, grazers) ¨ in vegetation



CHANGE OVER TIMEEcosystems are Dynamic NOT PERMANENT

DISTURBANCES :

Fire

WindstormSoil erosion

Disease

Insect cyclesHuman activities



CHANGE OVER TIMEEcosystems are Dynamic NOT PERMANENT

PROCESSES :

Change conditions of an ecosystem

Until relatively stable,

Self-replicating stage reached.

³equilibrium´

³climax´

³old-growth´ ( E&FB p. G-12 old grow th«forest that

has not been cut for decades or disturbed by

humans for hundreds of years.)



Ecological System Disturbance Type

UNIQUE RESULT :

Ecosystem

AQUATICTERRESTRIAL

2011 Lecture 4a Ecosystem Dynamics I

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