Species Competition and Predation - Ecological Systems - page 241

weather-dependent germination requirements. As weather patterns vary from year
to year, and sometimes very markedly, this means that guilds of annual plants often
show very marked variation from year to year in the relative abundances of the
plants that successfully germinate, grow, and flower [ 59 , 60 ]. Those that are not
successful in given year can bide their time as dormant seeds in the soil, with good
chances of success in some future year. In this way, intraspecific competition
becomes concentrated relative to interspecific competition when a sequence of
years of different environments are considered, as this behavior means that
a given individual is likely to experience more intraspecific competition than
interspecific competition from any given other species. The outcome is partitioning
of resources over time [ 59 ]. Indeed, it is possible to derive Lotka-Volterra
equations or very similar ones that represent the outcome of integration of short-
term fluctuations over time, even based on random fluctuations on that short
timescale [ 15 , 23 ].
The details of these effects of temporal partitioning are important. It is critical
for instance, that competition between individuals growing at different times does
not occur [ 61 ]. For this to be the case, the resources cannot carry over in time. For
instance, day and night foragers for a particular resource might still be competing
strongly even though they capture the resource at different times. This would be the
case if units of resource available at night are used by organisms in the day time if
they are missed by night time foragers. The result is that temporal differences in
foraging do not, in this case, concentrate intraspecific competition relative to
interspecific competition.
What is possible in this context for competition is also possible with apparent
competition, extending the essential symmetries for consideration of these pro-
cesses before. However, differences do occur because of the potential that apparent
competition works on a longer timescale [ 61 ]. For example, in annual plants with
seed predators, when a good seed crop causes buildup of seed predators through
high predator reproduction and survival, it is the seed crop the next year that
experiences the higher predator density. The seed crop the next year will likely
have different species composition due to species differences in response to the
temporally varying physical environment. Thus, the species that cause the predator
buildup are not necessarily the species experiencing higher predation. Intraspecific
apparent competition is not necessarily concentrated relative to intraspecific compe-
tition in his case. When the environment varies randomly from 1 year to the next,
predator buildup on good seed crops does not lead to effective temporal partitioning.
However, behavioral changes in predation rates can be on short timescales with the
potential that effective temporal partitioning can occur. Indeed, the theory implies
that frequency-dependent behavior and other density-dependent behaviors can in
some circumstances lead to temporal partitioning due to predation [ 50 , 51 ]. In these
cases, frequency-dependent behavior has two effects: an immediate and direct
effect of frequency dependence on the ratio of intraspecific to interspecific density
dependence, and a longer-term effect that involves an interaction between year to
year temporal variation in the physical environment and temporal variation in