Environmental Engineering Reference
In-Depth Information
flooded lower elevations (towards the left) as water levels decline. Fish 2 (good
disperser) moves ahead of Fish 1 (intermediate traits), Fish 3 (good exploiter),
and the crayfish. To the right, where the elevation is higher and fish density lower,
the invertebrates show a peak, as they are now free from fish predation. In addi-
tion, a remnant population of crayfish also survives, as they face less competition
from the fish.
As water levels continue to decline, the piscivorous fish will move to lower
elevation to the left where the cells are permanently flooded. As the water levels
begin to rise again (Fig.
18.5d
), some fish begin to follow the water movement,
resulting in small population peaks, with the crayfish leading, followed by Fish
3. Subsequently, all species follow the water movement to gradually occupy
most of the cells (Fig.
18.5e
), except for the last 12 or so cells at the right most
(Fig.
18.5f
), which are permanently dry. Piscivores occupy some of the cells in
the higher elevations when permitted by adequate water depth, but in low
density, as they do not have time to build up high biomass. In the simulated
food web, there are three distinct food chains observed (see Fig.
18.4
): periphyton-
fish/crayfish-piscivore, detritus-invertebrate-fish-piscivore, and detritus-crayfish-
piscivore. Because of these overlapping food chains, trophic cascades are not
clearly discerned. However, some top-down effects are observed in the simula-
tions as seen in Fig.
18.5d
, where high density of piscivores is associated with
reduced fish and crayfish density, and high density of invertebrates. In the vicinity
Pisc
Cray
F3
F2
F
F1
Invt
Peri
Detr
Nutr
Fig. 18.4 Trophic structure of the basic food web structure of the Southern Florida fish commu-
nity model.
Arrows
indicate predator/prey relationships.
Pisc
Piscivorous Fish,
Cray
Crayfish,
F1
,
F2
,
F3
Small fish species,
Invt
Invertebrates,
Peri
Periphyton,
Detr
Detritus,
Nutr
Nutrients
