Biology Reference
In-Depth Information
Other factors such as herbivory greatly influence diversity. However, niche
partitioning by the differential N use can reduce competition and lead to greater
N fluxes into the intertidal food web. The effect of resource-based niche
partitioning on diversity has been also suggested in terrestrial ecosystems (McKane
et al.
2002
). The nutritional status of aquatic primary producers has been found to
determine the efficiency of energy transfer through food chains (the so-called food
chain efficiency, FCE), with the carryover effects of algal quality across trophic
levels (Dickman et al.
2008
).
4.4.2 Slow-Growing vs. Fast-Growing Species
Aquatic plant communities are formed by a number of species representing
various growth strategies and life forms, and the contribution of the different
plant types to total autotrophic biomass and production is regulated by several
factors that influence growth and loss processes. The distribution of macroalgae
along nutrient gradients is typically characterized by slow-growing species in
nutrient-poor regions or seasons, while fast-growing, ephemeral species dominate
under nutrient-rich conditions (e.g., Kautsky et al.
1986
;Tayloretal.
1995
;
Borum and Sand-Jensen
1996
; see also Chap.
21
by Teichberg). The association
between high nutrient availability and increased dominance of ephemeral
macroalgae suggests that fast-growing species require high nutrient inputs to
sustain growth, while large, slow-growing species are better adapted to nutrient-
poor conditions. In support of this idea, Pedersen and Borum (
1996
)demonstrated
that ephemeral macroalgae suffered from N limitation during longer periods of
low N availability in summer than did slow-growing species. The observed
variation in N limitation among algae of different growth strategy could partly
be explained by species-specific differences in N requirements and storage capac-
ity (Pedersen and Borum
1997
). As an example, Lartigue and Sherman (
2006
)
found that, under fluctuating NO
3
discharges to an estuary, total N in the
nitrophillic fast-growing
Ulva lingulata
ranged from 2.6% to 6.4% dry weight,
while the slower growing
Gelidium pusillum
showed no significant variation in
total N content (3.8-4.1% dw). Additionally, Pedersen and Borum (
1996
)also
indicated that, compared to ephemeral species, slow-growing macroalgae were
better able to meet their N requirements by exploiting low external N
concentrations. Other studies have associated a higher position in the intertidal
with higher internal nitrate pools (Phillips and Hurd
2003
), higher NR activities
(Murthy et al.
1986
), and elevated nutrient uptake capacity, which may compen-
sate for periods of emersion (Hurd and Dring
1990
; Phillips and Hurd
2004
).
However, this association is not always valid, and contrasting results have also
been found (Young et al.
2009
).
