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6 Comparisons of Fronts with Terrestrial Boundaries …
Landscapes resemble mosaics composed by two kinds of structures: patches
and boundaries. Ecotones or boundaries are important structural features in
the landscape; they represent areas of transition, contact or separation between
the contrasting elements of a mosaic. Patches in the landscapes are connected
by fluxes of organisms, materials, energy, and information; and although ecotones are likely to occupy a relatively restricted part of the total volume, they are
expected to control the interactions of mosaics elements by modulating the connecting flows, thus becoming important control points (Cadenasso et al. 2003a, b).
Landscapes may be seen as dynamic systems of patches that are coalescing or disintegrating primarily through the expansion, fluctuation or erosion of boundaries
through time. Although some boundaries may be relatively stable in ecological
time, in other cases, interactions within biotic transitions will results in landscapes
characterized by fluctuations in the number, type and size of patches, along with
directional shifts from one patch type to another in response to local and regional
drivers (Peters et al. 2006). In terms of system dynamics, ecotones are locations
where the rates of ecological transfers (e.g. energy flow, nutrient exchange) change
abruptly in relation to those within the homogeneous units on either side. The
view of the oceans as a complex of different water masses looks analogous to the
perception of landscapes as mosaics, and the quoted general properties of ecotones
closely resemble that of the marine fronts. Following Gosz (1992), emergent
properties of the ecotones are more likely to occur where there are:
(1) Contrasting life history strategies or life forms on each side of the transition
(this is a common pattern in opposite sides of several marine frontal types,
for example the dominance of diatoms or dynoflagellates in each side of tidal
fronts; or that of neritic or oceanic planktonic forms across shelf-break fronts);
(2) Different constraints operating on organisms of each biome (contrasting physicochemical properties in several fronts comprise an acute set of constrains,
for example light versus osmotic constrains at each side in estuarine fronts;
temperature versus nutrients for plants in shelf-break fronts; light versus
nutrients at each side in tidal fronts);
(3) Different scale-related features in the two biomes (because of differences in
temperature, planktonic organisms may have different generation time at each
side of a front);
(4) Different heterogeneity features (for example vertical homogeneity versus
stratification of the water column present in each side of tidal fronts or shelfbreak fronts; different types of bottom substrates at each side of estuarine or
tidal fronts).
Though some boundary habitats in land (e.g. saltmarshes) have been reported as
hotspots of biological production (Canepuccia et al. 2011), biological productivity does not seem to be a general characteristics of terrestrial ecotones; in contrast,
marine fronts concentrate a disproportionate portion of the biological production
at sea and this is a main reason for their ecological importance.
Ecotones may serve either as barriers or corridors between gene pools, but this
does not necessarily imply that ecotones show higher diversity of species as
6 Comparisons of Fronts with Terrestrial Boundaries …
Landscapes resemble mosaics composed by two kinds of structures: patches
and boundaries. Ecotones or boundaries are important structural features in
the landscape; they represent areas of transition, contact or separation between
the contrasting elements of a mosaic. Patches in the landscapes are connected
by fluxes of organisms, materials, energy, and information; and although ecotones are likely to occupy a relatively restricted part of the total volume, they are
expected to control the interactions of mosaics elements by modulating the connecting flows, thus becoming important control points (Cadenasso et al. 2003a, b).
Landscapes may be seen as dynamic systems of patches that are coalescing or disintegrating primarily through the expansion, fluctuation or erosion of boundaries
through time. Although some boundaries may be relatively stable in ecological
time, in other cases, interactions within biotic transitions will results in landscapes
characterized by fluctuations in the number, type and size of patches, along with
directional shifts from one patch type to another in response to local and regional
drivers (Peters et al. 2006). In terms of system dynamics, ecotones are locations
where the rates of ecological transfers (e.g. energy flow, nutrient exchange) change
abruptly in relation to those within the homogeneous units on either side. The
view of the oceans as a complex of different water masses looks analogous to the
perception of landscapes as mosaics, and the quoted general properties of ecotones
closely resemble that of the marine fronts. Following Gosz (1992), emergent
properties of the ecotones are more likely to occur where there are:
(1) Contrasting life history strategies or life forms on each side of the transition
(this is a common pattern in opposite sides of several marine frontal types,
for example the dominance of diatoms or dynoflagellates in each side of tidal
fronts; or that of neritic or oceanic planktonic forms across shelf-break fronts);
(2) Different constraints operating on organisms of each biome (contrasting physicochemical properties in several fronts comprise an acute set of constrains,
for example light versus osmotic constrains at each side in estuarine fronts;
temperature versus nutrients for plants in shelf-break fronts; light versus
nutrients at each side in tidal fronts);
(3) Different scale-related features in the two biomes (because of differences in
temperature, planktonic organisms may have different generation time at each
side of a front);
(4) Different heterogeneity features (for example vertical homogeneity versus
stratification of the water column present in each side of tidal fronts or shelfbreak fronts; different types of bottom substrates at each side of estuarine or
tidal fronts).
Though some boundary habitats in land (e.g. saltmarshes) have been reported as
hotspots of biological production (Canepuccia et al. 2011), biological productivity does not seem to be a general characteristics of terrestrial ecotones; in contrast,
marine fronts concentrate a disproportionate portion of the biological production
at sea and this is a main reason for their ecological importance.
Ecotones may serve either as barriers or corridors between gene pools, but this
does not necessarily imply that ecotones show higher diversity of species as