Ecology and The North Atlantic Oscillation

Ecology and The North Atlantic Oscillation

Ecology and The North

Atlantic Oscillation

“In one sense the conditions of life may be said, not only to

cause variability, either directly or indirectly, but likewise to

include natural selection, for the conditions determine whether

this or that variety shall survive”

Charles Darwin (On the origin of species, 1859).

What is the North Atlantic


A large, long-term oscillating atmospheric mass

Action centers over the Azores and Iceland that

can vary temperatures and precipitation in North

America and Europe.

These variations mainly effect winter weather.

One of 13 worldwide atmospheric

teleconnections- pressure and circulation patterns

covering large geographical areas.

Most used for modeling because of its coherency

with the 700 year stable isotope record from

Greenland (GISP2 Ice core).

(Lamp and Peppler, 1987; Hurrell 1995)

The High and Low NAO

(a) Shows warm, wet winters in Europe and cold, dry winters in

North America, while (b) shows the opposite.

(Forchhammer et al, 1999)

The NAO index is quantified by the annual winter

(December through March) deviance from the average

difference between sea level pressures measured at

Lisbon (Portugal) and Stykkisholmur (Iceland).

(Forchhammer et al, 1999)

How Climate and the NAO

changes Ecology

Climate can either directly effect a specific trophic level, or may

become indirectly perpetuated beetween trophic levels.

(Post et al., 1999).

There are also direct and indirect effects on an

individual throughout its life history

(Albon et al., 1992;

Lindström 1999)

Climate Influence and Ecology

Can be divided into two main categories

Direct effects- more easily recognizable

and measurable (no lag time)

Indirect effects-Often involve climate

independent factors as well. (e.g.

population density)

(Milner et al., 1999).

Timing of Reproduction

One of the main components in determining

reproductive success is temperature at the time of


A number of studies document earlier breeding

dates for amphibians and birds located in the

North Hemisphere.

These studies by Beebee, Winkel, Crick et al., and

Brown et al. suggest these earlier breeding dates

are a direct response to climate warming

Variations in first breeding date of

amphibians and birds due to NAO


(a, Rana kl. esculenta; b, R. temporaria)

(c, Miliaria calandra; d, Phylloscopuscollybita).

Correlation between arrival of Norwegian

Skylark at breeding grounds in (Julian

date) and NAO index.

(Forchhammer et al., 1998)

Similar trends have been found between

plant reproduction time and the NAO.

Studies conducted with 13 woody and

herbaceous species and 139 populations

throughout Norway.

Show that plants bloomed 13-26 days earlier after

warm, wet winters (High NAO).

Woody species not as sensitive to NAO index


Naturally early bloomers were also more sensitive

to NAO.

(Post and Stenseth, 1999)

Solely Climate Influence?

From these examples it seems there is a

clear relationship between changes in

climate (temperature and precipitation) and

reproduction time.

But what about Biotic Factors?

Newer Climate models and studies have

incorporated climate and biological

processes simultaneously.

(Post et al., 2001)

Initial Climate Changes can be

perpetuated through later biotic


Soay Sheep in Scotland

(Forchhammer et al., 2001)

The initial climate conditions will have

impact on survival and fecundity. fecundity

Soay Sheep in Scotland

(Forchhammer et al., 2001)

Wolf pack size and moose

kills in Canada as a result of

Low NAO (increased snow).

(Post et al., 1999)

Moose population, decreased

browsing, and increased

understory fir growth.

(Post et al., 1999)

What to take home

A general understanding of:

1. The NAO

2. Direct/Indirect climatic effects

3. Wolf-Moose-Fir Ecosystem

4. Interrelationship between climatic and

biotic factors.


Albon, S.D., Clutton-Brock, T.H. and Langvatn, R. 1992: Cohort variation in reproduction and survival:

implications for population demography. In: Brown, R.D. (ed): The Biology of deer. Springer

Beebee, T.J.C., 1995: Amphibian breeding and climate. Nature, 374, 219-220.

Brown, J.L., Li, S.-H. and Bhagabati, N., 1999: Long-term trend toward earlier breeding in an American bird:

a response to global warming? Proc. Natl. Acad. Sci., 96, 5565-5569.

Crick, H.Q.P., Dudley, C., Glue, D.E. and Thomson, D.L., 1997: UK birds are laying eggs earlier. Nature, 388,


Darwin, C. 1859: On the origin of species. Murray.

Forchhammer, M.C., Post, E. and Stenseth, N.C., 1999: The North Atlantic Oscillation: interactions between

climatic and biological processes. NSN Newsletter, 24(4), 10-14.

Hurrell, J.W., 1995: Decadal trends in the North Atlantic Oscillation: regional temperatures and precipitation.

Science, 269, 676-679.

Lamb, P.J. and Peppler, R.A., 1987: North Atlantic Oscillation: concept and an application. Bull. Am.

Meteorol. Soc., 68, 1218-1225.

Lindström, J. 1999: Early development and fitness in birds and mammals. Trends in Ecology and Evolution,

14, 343-348.

Milner, J.M., Elston, D.A. and Albon, S.D. 1999: Estimating the contributions of population density and

climatic fluctuations to interannual variation in survival of Soay sheep. J. Anim. Ecol., 68, 1235-


Post, E., Peterson, R.O., Stenseth, N.C. and McLaren, B.E., 1999: Ecosystem consequences of wolf

behavioural response to climate. Nature, 401, 905-907.

Post, E. and Stenseth, N.C., 1999: Climatic variability, plant phenology, and northern ungulates. Ecology, 80,


Winkel, W., 1997: Long-term trends in reproductive traits of tits (Parus major, P. caeruleus) and pied

flycatcher (Ficedula hypoleuca). J. Avian Biol., 28, 187-190.

More magazines by this user
Similar magazines