Community Ecology Processes, Models, and Applications

since the ecosystems being connected often tran-
scend those types to which ecologists typically re-
strict themselves. Grassland ecologists rarely study
woodlands. Marine ecologists rarely study fresh-
water. Aquatic ecologists rarely study terrestrial
habitats. Above-ground ecologists seldom study
soil ecology. However, many of the organisms that
ecologists study readily traverse these boundaries
seasonally, or across their life span, and do so either
through behavioural means, such as migration,
through life-history shifts (sometimes called onto-
genetic niche shifts; Werner and Gilliam 1984), or,
like plants, just by growing with roots in the soil
and green parts above ground, linking the two sub-
systems of terrestrial ecology.
Organisms frequently move between ecosystem
types daily or seasonally for foraging, predator
avoidance, breeding, overwintering, etc. For exam-
ple, many birds, ungulates and marine mammals
are strong interactors (as both predators and poten-
tial competitors) that can migrate over very long
distances. The interactions of these organisms in
one local community can be the result of processes

that occurred in a very different ecosystem a very

long distance away.

Many species undergo life-history switches

which take them across different types of ecosys-

tems. For example, many pelagic marine fishes

spend their juvenile periods in estuaries, coastal

wetlands or freshwater streams. Additionally,

some species undergo much more dramatic onto-

genetic niche shifts, and in doing so can shift eco-

system types (e.g. aquatic to terrestrial) and trophic

roles (e.g. herbivore to carnivore) (reviewed in Wer-

ner and Gilliam 1984). These include a large num-

ber of insects (e.g.Diptera,Odonata,Megaloptera)

and amphibians that have aquatic larval and terres-

trial adult stages. In a recent study emphasizing the

important connections across ecosystem bound-

aries, Knightet al. (2005) found cascading effects

of fish in ponds to terrestrial plants through their

influence of dragonflies with ontogenetic niche

shifts. Specifically, dragonflies are strongly limited

by predatory fish in ponds, which translates into

fewer adult dragonflies near ponds with fish rela-

tive to near ponds without fish. In turn, adult

Pollinator

Dragonfly

Larval Dragonfly

Aquatic habitat Terrestrial habitat

Figure 5.4Schematic of the effects of fish in ponds on the adjacent terrestrial food web. Redrawn from Knightet al.
(2005).

INCREASING SPATIO-TEMPORAL SCALES 67