100 Influential Papers - page 14

Resetarits, W.J. & Chalcraft, D.R. (2007)
Functional diversity within a morphologically conservative genus of
predators: implications for functional equivalence and redundancy in
ecological communities.
Functional Ecology, 21, 793-804.
How far are species that are phylogenetically closely related, morphologically very similar,
with the same type of life cycle, and found in the same habitat ‘functionally equivalent’? The
authors investigated this issue using the three species of sunfish in the genus
Enneacanthus
.
These species are predators and are broadly sympatric in streams and pools on the eastern
seaboard of North America; often two species cohabit, and rarely three. In a three-month
experiment the various sunfish species were kept separately with three anuran species from
the tadpole stage in artificial ponds outdoors. In terms of effects on larval anurans only one
of three pairs of species could be considered functionally equivalent, and these two species
showed the greatest differences in growth and therefore metabolic demand. In terms of
relative yield total only one pair of species could be rated functionally equivalent, and their
effects on larval anurans were very different. This paper goes to the heart of how communities
are structured. In their analyses, the authors integrate physiology with ecology to test
ideas about functional equivalence. They challenge the commonly held view that functional
equivalence is widespread and should be expected. This issue is central to understanding the
relationships between diversity and ecosystem function.
Duncan Irschick
S ECT I ON TWO
COMMUN I TY AND ECOSYS T EM DYNAM I C S
18
19
Noy-Meir, I. (1975)
Stability of grazing systems:
an application of predator-
prey graphs.
Journal of Ecology,
63, 459–481.
Three strands in Noy-Meir (1975)
have continuing influence through to
the present. Firstly, Figure 5e showed
how two very different steady states
can arise when a given herbivore
stocking rate interacts with the forage
production from vegetation. Across
many different ecosystem-types, the
1970s were marked by increasing
appreciation of alternative states,
as also of disturbance regimes and
of lottery processes. Noy-Meir
(1975) manifested that same shift
in outlook for grazing systems.
Secondly, the Discussion gathered
evidence together from range and
pasture literature. As he put it ‘While
each of these pieces of evidence is
rather meagre, cumulatively they
indicate that some range and pasture
systems are discontinuously rather
than continuously stable.’ But range
management theory at the time did
not provide for alternative persistent
states. This discrepancy subsequently
stimulated development of state-
and-transition language (see web
site) in order to describe ecosystem
dynamics more realistically. Thirdly,
Figures 8-10 showed how as the
stocking rate approached closer
to maximum sustainable yield, the
plant-herbivore balance became more
vulnerable to year-to-year variation.
This idea that for natural resources
there is a choice between maximizing
yield and reducing vulnerability was
an important motivation for the now-
prominent concept of resilience in
social-ecological systems.
Mark Westoby
14
2
Grime, J.P. (1998)
Benefits of biodiversity effects on ecosystems: immediate, filter and
founder effects.
Journal of Ecology, 86, 902-910.
Since the mid 1990s there has been considerable focus on how plant biodiversity, including
species richness, drives ecosystem processes such as productivity, nutrient cycling
and decomposition. While many studies in the 1990s focused on immediate effects of
biodiversity, Grime’s 1998 paper was an important advance because it highlighted the
importance of distinguishing immediate effects driven by dominant species from filter and
founder effects emerging over longer periods when subordinate and transient species play
a role. Based on this approach, Grime proposed a ‘mass ratio hypothesis’, predicting that
the relative contribution of each species to ecosystem properties should be proportional to
its contribution to total primary productivity. Then ecosystem processes should be driven
primarily by traits of the dominant species (those contributing most to productivity) rather
than species richness of minor components. This concept has had an enduring impact for
three reasons. First, it provides plausible reasoning as to why plant community composition
rather than species richness may be a powerful driver of ecosystem functioning. Second, it
explicitly identifies a central role of plant traits in driving ecosystem processes, an area that is
attracting considerable effort. Third, it provides the conceptual underpinning for increasingly
widely used ‘community weighted’ approaches for quantifying plant traits and/or processes at
the whole community level.
David Wardle
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