Levels of Ecological Organization in Freshwater Systems

Population

Community

Ecosystem

Freshwater Ecosystems and Aquatic-Terrestrial Linkages

• To describe the “ecosystem concept”.

• To review recent advances in our understanding of the ecosystem ecology of freshwater systems, focusing on linkages between freshwater and terrestrial systems.

• To expand this discussion of freshwater-terrestrial linkages by examining the community-level implications of these linkages.

The Ecosystem Concept• Ecosystem = natural unit of the landscape with a “critical” level of homogeneity.

• Nutrients and energy cycle within ecosystems and move among ecosystems by abiotic process and biotic processes.

> Individuals / populations / communities are different ways of packaging energy and nutrients, and offer different perspectives on how energy and nutrients move within and among ecosystems.

• By tracking the input, internal cycling, and output of energy and nutrients, we can understand the fundamental role of an ecosystem in the larger landscape.

We have seen the influence of the ecosystem concept already:

What else can an ecosystem approach tell us about the connection between freshwater and terrestrial systems?

• Are streams just plumbing the landscape?

• Where does the C that supports lake productivity come from?

• Are streams just plumbing the landscape?

N

What else can an ecosystem approach tell us about the connection between freshwater and terrestrial systems?

The N problem

“Rivers deliver N to coastal

ecosystems”

“Streams and rivers are not

N-limited”

The LINX project

Spiraling Length

How far does the average N atom travel downstream before taken up by the biota?

N• S Low = Retentive

• S High = Leaky

(Peterson et al. 2001)

LINX Results

(Peterson et al. 2001)

LINX Implications

Streams help to prevent terrestrial N from reaching coastal ecosystems…

…especially headwater streams.

What else can an ecosystem approach tell us about the connection between freshwater and terrestrial systems?

• Where does the C that supports lake productivity come from?

Where does the C that supports lake communities come from?

Autochthonous

Allochthonous

Where does the C that supports lake productivity come from?

CO2

Respiration > Photosynthesis

The Experiment

13C(Pace et al. 2004)

• Corrected for 13C that could have come from photosynthesis.

• Allochthonous C accounted for 40-55% of POC and 22-50% of zooplankton.

The Results

(Pace et al. 2004)

Conclusions• Lakes themselves don’t produce enough C to

support the animals that live in them.

• Input of organic matter from the watershed allows for more secondary productivity than if lakes were isolated microcosms.

(Pace et al. 2004)

birds, bugs, and fishvs.

N and C

Population

Community

Ecosystem

How connected are stream and terrestrial communities?

The Experiment • Plots in and along a headwater stream on Hokkaido Island, Japan

• Forest is deciduous

(Nakano and Murakami 2001)

Predator CommunitiesForest Stream

• Physical conditions in stream and riparian zone:

Temperature

Light input

• Biological conditions in stream and riparian zone:

Availability of aquatic and terrestrial invertebrate “prey”

Flux of invertebrate prey from stream-to-forest and from forest-to-stream

Proportion of “allochthonous” prey in fish and birds (i.e., prey from where the predators aren’t)

(Nakano and Murakami 2001)

Temperature Results

(Nakano and Murakami 2001): Leaves on: Leaves off

Dai

ly m

ean

tem

per

atu

re (

ºC)

Terrestrial Predator Diet Results

(Nakano and Murakami 2001): Leaves on: Leaves off

Aquatic Predator Diet Results

(Nakano and Murakami 2001): Leaves on: Leaves off

Predator Diet

Results

(Nakano and Murakami 2001)

Conclusions • Both stream AND terrestrial predators use prey inputs from the other systems.

Maybe “freshwater” and “terrestrial” distinctions are less useful than we thought…

*The views expressed here are those of the person doing the talking.

Editorial* “It does appear that on many, many different human attributes-height, weight, propensity for criminality, overall IQ, mathematical ability, scientific ability - there is relatively clear evidence that whatever the difference in means-which can be debated - there is a difference in the standard deviation, and variability of a male and a female population.”

- Lawrence H. Summers President of Harvard

January 14, 2005

Editorial* • Mary E. Power, UC Berkeley

• Bobbi L. Peckarsky, Cornell and University of Wisconsin

• Margaret A. Palmer, University of Maryland

• Kate H. Macneale, NOAA

• Margaret A. Palmer, University of Maryland

• Emily S. Bernhardt, Duke University

• Judy L. Meyer, University of Georgia

• Carol L. Folt, Dartmouth College

• Nancy B. Grimm, Arizona State University

• Margaret B. Davis, University of Minnesota

• Jane M. Hughes, Center for Riverine Landscapes, Australia

*The views expressed here are those of the person doing the talking.

Editorial* “It does appear that on many, many different human attributes-height, weight, propensity for criminality, overall IQ, mathematical ability, scientific ability-there is relatively clear evidence that whatever the difference in means-which can be debated-there is a difference in the standard deviation, and variability of a male and a female population.”

- Lawrence H. Summers Former President of Harvard

January 14, 2005

WRONG