26.3 Biotic Patterns in Lakes
26.3 Biotic Patterns in Lakes
26.3.1 Historical Development
Historically, most scientific assessments of biotic
differences among lakes addressed the ability of
lakes to produce biomass of fishes or other harvestable resources (e.g., Matusek, 1978; Wetzel,
1983). More recently, limnologists and aquatic
ecologists have begun to examine the life-history
requirements and interactions among lake-dwelling
species and the specific mechanisms by which differences among lakes and changes within lakes
over time shape the organization and dynamics of
their biotic communities. For example, Murphy et
aI. (1990) compared the life history and ecological
strategies of submergent macrophyte species in
four physically contrasting lakes, and Evans et aI.
(1996) reconstructed the limnological changes that
could explain changes in fish populations in Lake
Simcoe, Ontario, over more than a century. The
groundbreaking work of Carpenter et al. (1985) on
trophic cascades has transformed lake ecologists'
views of trophic dynamics and revealed the disproportionate functional role that certain kinds of
animals or even particular species may play in
structuring in lake food webs. This change in perspective emphasizes that biotic communities in
lakes are not simply passively structured by the
chemical and physical template of the ecosystem,
but that species themselves can exert strong control on the diversity, productivity, and chemistry of
lakes.
26.3.2 Lake Biota in a
Landscape Context
Until recently, most comparative limnological
studies examined lakes as self-contained ecosystems, independent of their catchment settings and
hydrologically connected habitats. Increasingly,
scientists are examining the ecological organization
of lakes in the context of the landscape in which
they reside. For example, comparing headwater
lakes with small catchments to downstream lakes
with large catchments in northern Wisconsin, Kratz
et aI. (1997) found that hydrologic position is correlated with lake water retention, concentration of
silica and dissolved organic carbon, physical and
chemical response to drought, and biological factors, such as the vertical distribution of primary
production and fish species richness. Kratz et aI.
(1997) suggest that silica and calcium concentrations, which tend to be lower in headwater lakes
with small groundwater inflow rates, may influence
395
the abundance and ecological roles of freshwater
sponges and crayfish. The vertical distribution of
primary production in lake water columns is a function of water clarity and light penetration; thus
downstream lakes with higher nutrient and organic
carbon loads may have shallower productive zones
than do headwater lakes with deeper photic zones.
Lower fish species richness in Wisconsin headwater lakes compared with downstream lakes might
stem from the tendency for downstream lakes to be
larger, implying that in larger lakes more area of
each habitat type is available to support rare species
(Kratz et al., 1997). However, because connectivity with the drainage network and other lakes is
clearly lower for headwater lakes, lower richness
in headwater lakes could reflect the relative biogeographical isolation and lower probability of fish
species colonization of these lakes (Tonn et aI.,
1990; Kelso and Minns, 1996). This is consistent
with the relative ease of establishment of many fish
or other aquatic predators newly introduced in such
lakes (Tonn et aI., 1983; Moyle, 1986) and the major ecological rearrangements that often result from
such introductions (e.g., Spencer et aI., 1991).
26.3.3 Ecosystem Influences and
Alterations of Lake Biotas
Managers and scientists engaged in environmental
assessment should recognize and address the limitations and potential pitfalls of any approach that
relies exclusively on inferring general or potential
patterns in the biota of lakes based on geographicalor physical indices. Globally, few but the very
smallest lakes have escaped major ecological disruption from human introduction of nonnative
fishes, macrophytes, crayfishes, or other organisms. Establishment of a single predatory fish
species can cause massive direct and indirect alterations of ecological structure and function that
reverberate through several ecological levels both
up and down the trophic web (Zaret, 1982; Carpenter et aI., 1985; Moyle, 1986). The effects of introduced species that play key roles in the food web
can spin off to alter terrestrial, riverine, and lake
communities, as in the case of the introduction of
the mysis shrimp to lakes outside their native range
(Spencer et aI., 1991). Furthermore, despite longstanding and familiar theories of pond to meadow
succession, little is yet known about the long-term
trophic evolution of larger lakes and the extent to
which trophic succession is sensitive or reversible
in response to changing environmental factors. This
is an area of prolific research activity; recent studies suggest not only that human influences on lake
26.3 Biotic Patterns in Lakes
26.3.1 Historical Development
Historically, most scientific assessments of biotic
differences among lakes addressed the ability of
lakes to produce biomass of fishes or other harvestable resources (e.g., Matusek, 1978; Wetzel,
1983). More recently, limnologists and aquatic
ecologists have begun to examine the life-history
requirements and interactions among lake-dwelling
species and the specific mechanisms by which differences among lakes and changes within lakes
over time shape the organization and dynamics of
their biotic communities. For example, Murphy et
aI. (1990) compared the life history and ecological
strategies of submergent macrophyte species in
four physically contrasting lakes, and Evans et aI.
(1996) reconstructed the limnological changes that
could explain changes in fish populations in Lake
Simcoe, Ontario, over more than a century. The
groundbreaking work of Carpenter et al. (1985) on
trophic cascades has transformed lake ecologists'
views of trophic dynamics and revealed the disproportionate functional role that certain kinds of
animals or even particular species may play in
structuring in lake food webs. This change in perspective emphasizes that biotic communities in
lakes are not simply passively structured by the
chemical and physical template of the ecosystem,
but that species themselves can exert strong control on the diversity, productivity, and chemistry of
lakes.
26.3.2 Lake Biota in a
Landscape Context
Until recently, most comparative limnological
studies examined lakes as self-contained ecosystems, independent of their catchment settings and
hydrologically connected habitats. Increasingly,
scientists are examining the ecological organization
of lakes in the context of the landscape in which
they reside. For example, comparing headwater
lakes with small catchments to downstream lakes
with large catchments in northern Wisconsin, Kratz
et aI. (1997) found that hydrologic position is correlated with lake water retention, concentration of
silica and dissolved organic carbon, physical and
chemical response to drought, and biological factors, such as the vertical distribution of primary
production and fish species richness. Kratz et aI.
(1997) suggest that silica and calcium concentrations, which tend to be lower in headwater lakes
with small groundwater inflow rates, may influence
395
the abundance and ecological roles of freshwater
sponges and crayfish. The vertical distribution of
primary production in lake water columns is a function of water clarity and light penetration; thus
downstream lakes with higher nutrient and organic
carbon loads may have shallower productive zones
than do headwater lakes with deeper photic zones.
Lower fish species richness in Wisconsin headwater lakes compared with downstream lakes might
stem from the tendency for downstream lakes to be
larger, implying that in larger lakes more area of
each habitat type is available to support rare species
(Kratz et al., 1997). However, because connectivity with the drainage network and other lakes is
clearly lower for headwater lakes, lower richness
in headwater lakes could reflect the relative biogeographical isolation and lower probability of fish
species colonization of these lakes (Tonn et aI.,
1990; Kelso and Minns, 1996). This is consistent
with the relative ease of establishment of many fish
or other aquatic predators newly introduced in such
lakes (Tonn et aI., 1983; Moyle, 1986) and the major ecological rearrangements that often result from
such introductions (e.g., Spencer et aI., 1991).
26.3.3 Ecosystem Influences and
Alterations of Lake Biotas
Managers and scientists engaged in environmental
assessment should recognize and address the limitations and potential pitfalls of any approach that
relies exclusively on inferring general or potential
patterns in the biota of lakes based on geographicalor physical indices. Globally, few but the very
smallest lakes have escaped major ecological disruption from human introduction of nonnative
fishes, macrophytes, crayfishes, or other organisms. Establishment of a single predatory fish
species can cause massive direct and indirect alterations of ecological structure and function that
reverberate through several ecological levels both
up and down the trophic web (Zaret, 1982; Carpenter et aI., 1985; Moyle, 1986). The effects of introduced species that play key roles in the food web
can spin off to alter terrestrial, riverine, and lake
communities, as in the case of the introduction of
the mysis shrimp to lakes outside their native range
(Spencer et aI., 1991). Furthermore, despite longstanding and familiar theories of pond to meadow
succession, little is yet known about the long-term
trophic evolution of larger lakes and the extent to
which trophic succession is sensitive or reversible
in response to changing environmental factors. This
is an area of prolific research activity; recent studies suggest not only that human influences on lake