Aj. Weatherby et al., COEXISTENCE AND COLLAPSE - AN EXPERIMENTAL INVESTIGATION OF THE PERSISTENT COMMUNITIES OF A PROTIST SPECIES POOL, Journal of Animal Ecology, 67(4), 1998, pp. 554-566
1. Using protists in laboratory microcosms we investigated the long-te
rm coexistence of combinations of species from a six species set to ad
dress the following questions: (i) What proportion of the possible com
munities from the species pool are persistent? (ii) From how many init
ial states are each of these persistent communities obtained? (iii) Wh
at are the impacts of individual species on community collapse? (iv) C
an the behaviour of the system be characterized by a simple set of rul
es? (v) To what extent does knowledge of the results from the pairwise
species combinations allow prediction of the outcomes of the more spe
cies-rich sets? 2. Replicated microcosms were set up with each of the
63 possible combinations of species from a pool of six protist species
(three bacterivores, two predators and one omnivore) along with a mix
ed bacterial flora. Microcosms were maintained, with nutrient replenis
hment, for over 100 days until a constant species composition was reac
hed. 3. Forty-seven of the 63 starting combinations showed a repeatabl
e collapse to one of eight communities (including the 'empty' communit
y - containing just bacteria). The number of starting combinations lea
ding to each of these persistent communities varied from 17 down to on
e. Extinction rates were higher in more species-rich systems. 4. The e
ffects of each species in determining the composition of the persisten
t community were characterized as to whether they were present in the
final set or not, and whether their occurrence in the starting combina
tion had any effect on the eventual presence or absence of others. Und
er this classification the larger species seem to be more influential
in shaping the final community. 5. The collapse from the initial speci
es composition to that at the end could be stated in terms of four sim
ple rules in 34 of the 47 starting combinations for which a persistent
community could be defined. 6. Using the outcomes from the single-spe
cies and two-species starting sets only, the eventual states to which
the larger communities collapsed could be correctly predicted in 27 ou
t of the 31 starting combinations containing three or more species for
which persistent communities could be defined.