A number of community variables can be examined from the standpoint of their variability
with respect to diversity. Among these are species composition and food web
structure. Simpler communities, in terms of their species composition and food web structure,
often appear to be more stable than complex communities (e.g., May 1973, 1983).
Boucot (1990) noted that simple marine communities in the fossil record continue across
sedimentary discontinuities more often than do complex marine communities. Boucot
(1990) also noted that particular taxonomic associations typically recur over larger areas
for 106
–107
yrs, indicating a high degree of stability within environmental constraints. The
variety of successional pathways leading to multiple endpoints (Horn 1981, Whittaker
1953) has indicated that many communities do not necessarily recover their predisturbance
composition or food web structure, although some mechanisms lead to positive
feedback between disturbance and community organization (Schowalter 1985, Schowalter
et al. 1981a, Shugart et al. 1981).
Modeling approaches have led to contrasting conclusions. May (1973, 1983) and Yodzis
(1980) reported that more complex communities were more vulnerable to disruption by
perturbations in any particular species population because of their propagation through
the network of interactions involving that species. However, de Ruiter et al. (1995) incorporated
the patterning of interaction strengths in real communities and found that
the simultaneous occurrence of strong top–down regulation of lower trophic levels and
strong bottom–up regulation of higher trophic levels imposed stabilizing effects on interaction
strengths. E. Evans (1988) found that grasshopper assemblages converged toward
significantly greater similarity in structure following fire in a grassland ecosystem than
was predicted by a random model. Fukami et al. (2001) modeled compartmentalized communities
and demonstrated that increasing diversity increased similarity in composition
among local communities and that greater similarity improved reliability of community
structure and function.
A number of studies, especially in aquatic and grassland systems, have demonstrated
that higher diversity permits compensatory responses in species composition (e.g., replacement
of intolerant species by more tolerant species) that maintain ecosystem productivity,
which underlies ecosystem structural and functional attributes (e.g., Gonzalez
and Loreau 2009). Although Houlahan et al. (2007) reported that most studies of natural
systems show positive covariances among species, rather than the negative covariances
predicted by earlier compensatory dynamics models, Loreau and de Mazancourt (2008)
and Gonzalez and Loreau (2009) argued that positive covariances could be consistent
with compensatory dynamics when various populations in the community are inherently
synchronized by strong environmental forcing and/or fluctuating abundance of a dominant
species