Implications of Soil Biodiversity for Sustainable Organic Matter Management - Sustainable Management of Soil Organic Matter - page 337

Table 5.1. Hypotheses relating to diversity-function relationships.

Stylized diversity(x)-
function(y) relationship Hypothesis Basis References a

Redundancy As long as all functional groups are

represented, system functioning is
independent of diversity

Lawton and
Brown, 1994

Rivet All species make a significant contribution

to function and that a decrease in diversity
leads to a progressive decline in function

Lawton,
1994

Predictable
change

Change in diversity will result in an
alteration in function, which is predictable
given a prioriknowledge of the trophic
structure, biomass and principal
relationships between the biotic
components within a system

Mikola and
Setälä, 1998

Idiosyncratic Changes in diversity will result in

changes in function, but the direction and
magnitude of any response are inherently
unpredictable

Lawton,
1994

Gas box The biota act as an averaging engine

by-passing the ecological hierarchy; function
is considered as an integrated process

Andrén
et al., 1999

a See Mikola and Setälä (1998) for further general discussion.

Initial research claimed to demonstrate benefits to ecosystem function
from higher biodiversity (Naeem et al ., 1994; Tilman and Downing 1994;
Tilman et al ., 1997). However, there is a growing body of experimental
evidence that the functional characteristics of component species are at
least as important as the number of species per se for maintaining critical
ecosystem processes (Grime, 1997; Wardle et al ., 1997; Bardgett and
Shine, 1999). However, it is not known how much biodiversity is needed
to ensure continuance of specific soil functions. There is currently little
published experimental data which rigorously tests these four hypotheses
in below-ground systems, and research from the perspective of soil OM
dynamics is particularly sparse.