177
See also: Evolution by natural selection 24–31 ■ Predator–prey equations 44–49 ■ Optimal foraging theory 66–67 ■ Animal
ecology 106–113 ■ Open community theory 174–175 ■ Niche construction 188–189 ■ Metacommunities 190 –193ORGANISMS IN A CHANGING ENVIRONMENT
also consume oak-leaf insects
and proposed that these oak-leaf
feeding birds could be grouped into
a “guild”—the “oak-foliage gleaners
guild”—because they exploited the
same resource.Shared resources
Root defined a guild as a group of
species that “exploit the same class
of environmental resources in a
similar way.” It does not matter
whether species in a guild are
related or not—all that matters is
how they use their environment.
They do not even have to occupy
the same niche; they just have to
use the same resource.
Guilds are typically identified
by the food resource they have in
common, although it could be any
other resource that they share.
Sharing the same resource means
that guild members often compete
with one another, but they are not
necessarily in constant competition.
For example, although they may
compete for the same food, on other
occasions they might cooperate to
deal with predators.The guild concept was a major
breakthrough in thinking about
connections between organisms
in ecosystems. The theory implied
that the entire functioning of an
ecosystem could be understood by
identifying all the guilds within it.
Although that was potentially a
huge undertaking, ecologists have
now managed to identify many
more guilds that confirm links
between species. For example,
the birds of North America can
be grouped into guilds of gleaners,
excavators, hawkers, aerial chasers,
and scavengers.Broad associations
In the rush to identify guilds, there
was some confusion over just what
the term meant. By the 1980s, the
American ecologists Charles
Hawkins and James MacMahon
felt the need to redefine the term.
They argued that the words “in a
similar way” should be dropped
from Root’s original definition. It
does not matter, they maintained,
whether an organism removes a
tree leaf to build a nest or for food.
It is the resource of the tree leaf
that matters rather than the way
it is utilized. Either way, the leaf-
users belong to a common guild
because they are exploiting the
same resource. ■Species
that
share a
resource
can be
grouped
in a guild.Different
species may
exploit
the same
resource.These species
are linked
by their
shared
resource.Richard B. Root
American biologist and
ecologist Richard Root was
born in Dearborn, Michigan,
in 1936. He grew up on a farm,
exploring nature and longing
to know “how the woods
worked.” By the time he
completed his doctorate at the
University of Michigan, Root
was already a knowledgeable
ecologist. His 1967 thesis on
the Blue-gray Gnatcatcher, in
which he introduced the key
concept of the guild, cemented
his reputation. Root was
invited to join the staff of
Cornell University, where he
taught biology and ecology.
While there, he researched
the relationship between
arthropods (a large group of
invertebrates including insects
and arachnids) and goldenrod
flowers. Root received many
awards during his career,
including the Ecological
Society of America’s Eminent
Ecologist award in 2003
and its Odum award in 2004....does it matter that a
particular insect species
is captured by a silken
spider web as opposed
to a bird’s beak?
Charles Hawkins and
James MacMahon
Key works1967 “The niche exploitation
pattern of the Blue-gray
Gnatcatcher”US_176-177_Ecological_guild.indd 177 12/11/18 6:25 PM