NEWS
between grazing-induced changes in
dominance and changes in species rich-
ness.
Where herbivores decreased the rela-
tive abundance (biomass, cover) of
dominant species, plant species rich-
ness increased, while increased domi-
nance caused a decline in species rich-
ness. This relationship holds true across
all continents and their assortment
of wild and domestic herbivores, and
across the rainfall gradient.
Change in dominance explains posi-
tive and negative herbivore impacts on
plant biodiversity across vastly different
grassy systems globally by considering
the traits of the dominant plants – those
characteristics of a species that impart
competitive advantage, that result in re-
source limitation for others, and which
allow grazing tolerance or avoidance.
Strong dominance by just a few species
is a nearly universal feature of herba-
ceous ecosystems.
As a consequence, this new thinking
points to ‘dominance management’ –
essentially altering competition for re-
sources using herbivores as an effective
conservation strategy.
Figure 2: Map of the 252 site localities included in the meta-analysis, with mean annual rainfall shown. Many sites overlap,
so not all are visible.
Figure 3 (a - d): Herbivore type and number varied among exclusion sites, and
included domesticated cattle, sheep, goats, burros and horses, as well as native
wildlife such as bison, caribou, kangaroo and the full complement of large African
herbivores.
Figure 4: The change in species rich-
ness (as a measure of diversity) be-
tween grazed and ungrazed treatments
at each of the 252 sites correlated more
strongly with change in the biomass or
cover of dominant species than with
precipitation (as a proxy for system
productivity).
Each dot represents a single site.
Grassroots
Vol 19
No 1
March 2019
22