Oceanography | June 2016
QUARTERDECK
The great American marine ecologist
Robert T. (Bob) Paine passed away in
Seattle on June 13, 2016. During the last
half century, Bob introduced some of the
most important conceptual advances in
community ecology, perhaps none more
influential than that of the keystone spe-
cies. A keystone species is one that has
a disproportionately large effect on its
surrounding community. Such a species
plays a critical role in maintaining the
community’s structure, affecting many
other organisms, and helping to deter-
mine the types and numbers of various
other species found in that community.
The keystone species concept came
to Bob as he pondered the spectacu-
lar wave-swept shores of the Pacific
Northwest’s rocky intertidal. Arriving at the University
of Washington in 1962 as a new assistant professor, Bob
applied the concepts that he had learned at the University of
Michigan from three of the most influential ecologists of their
day—Nelson Hairston, Fred Smith, and Larry Slobodkin. In
1960, this trio published one of the all-time classic papers in
ecology—“Community Structure, Population Control, and
Competition.” This paper, which is referred to by most ecologists
today simply as “HSS,” laid the foundation for a career Bob spent
experimentally tinkering in the ecology between Pacific tides.
HSS hypothesized that the world was green because the pop-
ulations of herbivorous species grazing on green plants were
held in check by predatory species higher up the food chain.
This revolutionary idea tipped the world of community ecol-
ogy upside down. Prior to HSS, most ecologists viewed natural
communities as being structured from the bottom up, with the
amount of energy flowing from lower to higher trophic levels
in the food chain determining community structure. Bob took
this top-down worldview from the land-locked campus of the
University of Michigan and applied it to the familiar but poorly
understood rocky shores of Washington state.
Fifty years ago this year, Bob published his own classic paper,
“Food Web Complexity and Species Diversity,” which sketched
out ideas that would later become known as the keystone spe-
cies and trophic cascade concepts. Bob had found that by
experimentally removing the predatory
ochre sea star, Pisaster ochraceus, from
the seashore, he could fundamentally
alter the intertidal community’s struc-
ture and diversity. The effects of Pisaster’s
removal cascaded down the food chain,
eliminating certain species and alter-
ing the web of interactions occurring
among the rocky shore’s other inhab-
itants. To future generations of ecolo-
gists being trained around the world,
Pisaster became known as the quintes-
sential keystone predator. This concept
was subsequently extended to include
other species whose removal or addition
disproportionately affected the commu-
nities around them.
Similar to the keystone species he
studied, Bob’s intellectual contributions had a disproportion-
ate effect on the field of community ecology. Not only did he
develop important theoretical concepts, he also demonstrated
the value of field experiments in testing ecological theory. By
example, Bob became the progenitor of a vast school of experi-
mental ecologists (Figure 1), most working in marine environ-
ments, but some also venturing into terrestrial and freshwater
realms. Bob’s influence spread well beyond the direct descen-
dants on his academic family tree. In fact, many attribute Bob’s
promotion of the field experimental approach as one of the
great turning points in twentieth century ecology.
As fundamental as Bob’s contributions have already been
to basic ecological theory, their application to practical, real-
world problems will play an increasingly important role as soci-
ety attempts to understand and grapple with the problems aris-
ing in our rapidly changing ocean. For example, during the
persistent ocean heat wave that has plagued coastal waters
from California to Alaska during the past three years (see
article by Cavole et al., 2016, in this issue, for further discus-
sion), there has been a collapse of most sea star populations in
rocky intertidal and shallow subtidal habitats. Sea star wast-
ing syndrome appears to be responsible for a majority of these
temperature-mediated disease outbreaks (Pfister et al., 2016).
Laying waste to not only Pisaster in the intertidal, but also to
the subtidal keystone predator, the sunflower star Pycnopodia
Wading in the Footsteps
of an Ecological Giant