Biology Reference
In-Depth Information
earth's atmosphere and the resulting ocean acidification (Feely et al. 2004 ; Orr et al.
2005 ) and direct negative effects on calcifying algae. The difficulty is that for
noncalcifying algae, elevated inorganic carbon has positive effects on some species
and not others, and that these nonuniform effects among alternate species (review
by Gao and McKinley 1994 ) have relatively unexplored consequences to competi-
tive hierarchies, particularly if growth is limited by sources of inorganic carbon.
If competitive interactions are reduced by the increasingly novel conditions
brought by human activities, then the persistence of entire biological communities
is increasingly likely to be disrupted. Such phase shifts are not uncommon, but
anticipating them has been problematic because many involve indirect effects for
which the impact of one species (e.g., turfs) on another (e.g., kelp) requires
knowledge of a third element that is inadequately understood (e.g., synergies
among pollutants). The strength of competition (e.g., dominance of kelp over
turfs) is important to understand because it identifies the conditions in which turfs
expand. The mere presence of foundation species may not always maintain their
competitive strength over turfs. As canopies are thinned, reduced in size, or
fragmented, their positive effects are reduced and the associated environmental
conditions become more similar to those experienced outside the canopy (Jackson
and Winant 1983 ; Bruno and Bertness 2001 ). Under these conditions, turfs expand
to dominate space and inhibit the recruitment of kelp (Gorman and Connell 2009 ;
Connell and Russell 2010 ), leading to phase shifts over multiple generations
(Connell et al. 2008 ). Therefore, the maintenance of intact populations of founda-
tion species seems critical to the strength of interaction (i.e., continued dominance
over kelp inhibitors) and ensuing maintenance of community structure and function
(Bruno and Bertness 2001 ). The competitive balance between species is often
shifted by the abiotic environment which alters the relative abilities of algae to
recruit to and retain space. Hence climate change seems set to bring change to
competitive processes as we currently understand them.
7.4 Concluding Remarks
In conclusion, competition within and among marine macroalgae is a deterministic
influence in establishing patterns of biogeography, regulating growth and reproduc-
tion, and in maintaining populations at or below their carrying capacities. It is
important to setting species range limits, governing how populations will respond
to disturbances, and in structuring coastal ecosystems. However, the direction,
strength, and importance of these competitive interactions vary considerably with
species identity, the location where these interactions take place, and with changes to
the physical and biological environment. Many species have evolved morphologies
that enable them to better access the resources, and thus outcompete their neighbors,
but these morphologies also may make them more susceptible to environmental
stresses, thereby temporarily altering competitive hierarchies and ameliorating the
effects of limited resources. Even so, numerous studies have demonstrated that
Search WWH ::




Custom Search