of chaotic dynamics in a food web. Whether such
chaotic dynamics also frequently occur in natural
plankton communities still needs to be seen though,
as the experimental set-up prevented many types of
interactions between biota and abiotic factors (such
as sediments). One can imagine that fluctuations in
external forcing factors, such as light and tempera-
ture, may overrule the potential for chaotic dynam-
ics in such systems.
Recently, another way out of the ‘paradox of the
plankton’, or the ‘principle of competitive exclu-
sion’ (no more species are expected to coexist than
the number of limiting resources), has been offered
by the same research group. Classic explanations
for coexistence of plankton species have explored
light, nitrogen, phosphorus and silicon as the main
limiting resources, leading to an expectation of only
few species to coexist, each limited by a different
resource. However, different algae species seem to
have specialized on different wavelengths of the
light spectrum, which therefore is in fact a whole
class of resources (Stompet al.2007a,b). These ‘col-
ourful niches’ seem to play a yet underestimated
role in the coexistence of plankton species.
Of course, other mechanisms that minimize the
importance of competition among species can also
operate to maintain diversity in spatially structured
or well-mixed environments. Perhaps the best known
of these mechanisms is keystone predation (Paine
1966), in which consumers feed preferentially on com-
petitively superior species and prevent competitive
exclusions of weaker competitors (Leibold 1996).01a2341006050403020(^0200)
Time (days)
Species abundances
300
b 55
50
45
40
35
20
6
25
Species 5
Species 3^25
9
30
12
35
15
(^4018) Species 1
30
c
150
120
90
60
30
0
Total biomass
0
100
Time (days)
200 300
10
5
Figure 1.4(a) Example of coexistence in a system of chaotically fluctuating consumptive competitors. Reprinted with
permission from Macmillan Publishers Ltd:Nature, 407–10, J. Huisman & F.J. Weissing,#1999. (b) Populations of three
species orbit around a strange attractor, typical of chaotic dynamics. (c) Although the populations fluctuate chaotically,
total biomass summed over all species is invariant over time.
14 SHAPE AND STRUCTURE