Stephen Maberly, Alex Elliott, Peter Henrys, Ian

Jones, Stephen Thackeray & Ian Winfield

Lake Ecosystems Group

Centre for Ecology & Hydrology, Lancaster, UK

Echoes in the ecosystem: top-down & bottom-up responses of Windermere to

environmental perturbation

Jonathan Grey & Peter Smyntek

Queen Mary University of London, UK

Top-down & bottom-up multiple stressors

Maberly & Elliott (2012) Freshwater Biology 57, 233-243

Nutrients (& toxins)

Acid (& nutrients)

Climate change

Natural variability in weather

Bo

tto

m-u

p

Top

-do

wn

Windermere

Photos from

FBA Image

Archive

• England’s largest lake

• Two basins: deeper, less productive North

and shallower more productive South

• One of the most intensively studied lakes in

the world

• Long-term data and archives from early

1900s and regular sampling for range of

variables since 1945

• Freshwater Biology Special Issue Feb 2012

57 (2)

Windermere as a model system

Mean winter SRP (mg m-3

)

0

5

10

15

20

25

30

1950 1960 1970 1980 1990 2000 2010

Year

North Basin

South Basin

6

8

10

12

1950 1970 1990 2010Year

Mean surface temperature (oC)

North Basin

South Basin

Nutrient enrichment Warming Expansion of non-native species

0

1000

2000

3000

4000

5000

6000

1990 1995 2000 2005 2010

Ab

un

dan

ce (f

ish

h

a-1

)

Year

Warmer water

Reduction in zooplankton

Increase in roach

Increase in phytoplankton

Reduction in Arctic charr

Reduction in oxygen at

depth

Stronger stratification

Increased internal P-

load

Planktivores

Zooplankton

Phytoplankton

Chemistry

Physics

Changes in Pike diet

Carnivores

Echoes in the ecosystem

Climate change

Creating the model 10 km2 Database and Atlas of Freshwater Fish (1973-1989) + Met Office UKCP09

daily 5 km2 gridded observed mean air temperature (1973-

1989)

Generalised Linear Model (GLM) with binomial

response

Probability of roach presence

Testing the model

Compared model prediction with observed presence (1990-2006; new sites in yellow) using gridded air temperature from that period

Predicted response Percentage

Presence/absence correct 81.9%

Wrongly predicted presence 7.3%

Wrongly predicted absence 10.9%

A probability threshold of 0.876 was optimal for classifying presence or absence of roach

Predicted expansion of Roach habitat

Probability of presence

Air temperature increase (°C)

1 2 4 3

Changed predation on zooplankton?

Pre

dat

ors

G

raze

rs

Foo

d/T

emp

erat

ure

The hypothesis

Climate change

Warmer water

Reduction in zooplankton

Increase in roach

Increase in phytoplankton

Reduction in Arctic charr

Reduction in oxygen at

depth

Prolonged stratification

Increased internal P-

load

Planktivores

Zooplankton

Phytoplankton

Chemistry

Physics

Changes in Pike diet

Carnivores

Mean zooplankton (No. dm-3

)

0

2

4

6

8

10

12

14

16

18

1950 1970 1990 2010

North Basin

South Basin

Bo

tto

m-u

p

Top

-do

wn

Data from 1991-2010 Modelling using GAMS on de-seasonalised data with

each driver allowed to interact with month

Top-down and bottom-up effects on Eudiaptomus

Seas

on

ally

dtr

end

ed E

ud

iap

tom

us

abu

nd

ance

Seasonally detrended fish consumption

Seasonally detrended chlorophyll concn

Top model assessed using

AIC

Changing fish populations

Water temperature

Roach numbers

Zooplankton

density in summer

Phytoplankton (Chla) in summer

Arctic charr numbers

Oxygen concentration

at depth

Arctic charr numbers

30%

4%

12%

6%

Path-analysis for the North Basin (Bayesian belief

network implemented in Winbugs)

Effects on the top predator of changing fish populations?

The hypothesis

Climate change

Warmer water

Reduction in zooplankton

Increase in roach

Increase in phytoplankton

Reduction in Arctic charr

Reduction in oxygen at

depth

Prolonged stratification

Increased internal P-

load

Planktivores

Zooplankton

Phytoplankton

Chemistry

Physics

Changes in Pike diet

Carnivores

The changing diet of pike

Pike percent diet composition in the 1970s and 2000s

• Historically eutrophication has been the major stressor on Windermere

• Currently climate change is altering niches and creating both top-down and bottom-up effects in the lake

• Warming water has ‘echoed through the ecosystem’ increasing the niche for roach with knock-on effects at different levels in the food web

• Climate change is a global phenomenon and so cannot be managed locally. Further nutrient reduction may ameliorate some of the effects of climate change but species at the southern-end of their geographic range are likely to be lost and species at the northern-end will become more abundant.

• There are likely to be ecological surprises as the complex interactions between the external environment and different components of the lake unfold.

Summary

Acknowledgements

• This work was funded by NERC Grant NE/H000208/1: “Whole lake responses to species invasion mediated by climate change” (http://www.windermere-science.org.uk/).

• Many thanks to everyone involved in maintaining the Cumbrian Lakes long-term monitoring programme, past and present.

• Thank you for your attention!