Lotic Habitats

Streams vary greatly in gradient, current velocity, width, depth, flow, sinuosity, cross-sectional area, and substrate type, depending on their position in the landscape with respect to geology, climate, and the basin area they drain. Anyone who has spent much time around or wading in streams is aware that these can be extremely diverse habitats, often manifesting great

TABLE II Aquatic Habitat Classification System

General category

Specific category

Description

Lotic—erosional (running-water riffles)

Lotic—depositional (running-water pools and margins)

Lentic—limnetic (standing water) Lentic—littoral (standing water, shallow-water area)

Sediments

Vascular hydrophytes Detritus

Sediments

Coarse sediments (cobbles, pebbles, gravel) typical of stream riffles. Vascular plants growing on (e.g., moss, Fontipalis) or among (e.g., pondweed,

Potamogeton pectinatus) coarse sediments in riffles. Leaf packs (accumulations of leaf litter and other coarse particulate detritus at leading edge or behind obstructions such as logs or large cobbles and boulders) and debris (e.g., logs, branches) in riffles. Fine sediments (sand and silt) typical of stream pools and margins.

Vascular hydrophytes Vascular plants growing in fine sediments (e.g., Elodea, broad-leaved species of

Lentic—profundal (standing water, basin) Beach zone

Detritus Open water Erosional

Vascular hydrophytes

Emergent zone

Floating zone

Submerged zone

Sediments

Sediments

Freshwater lakes Marine intertidal

Potamegeton, Ranunculus).

Leaf litter and other particulate detritus in pools and alcoves (backwaters).

On the surface or in the water column of lakes, bogs, ponds.

Wave-swept shore area of coarse (cobbles, pebbles, gravel) sediments.

Rooted or floating (e.g., duckweed, Lemna) aquatic vascular plants (usually with associated macroscopic filamentous algae).

Plants of the immediate shore area (e.g., Typha, cattail), with most of the leaves above water.

Rooted plants with large floating leaves (e.g., Nymphaea, pond lily), and nonrooted plants (e.g., Lemna).

Rooted plants with most leaves beneath the surface.

Fine sediments (sand and silt) of the vascular plant beds.

Fine sediments (fine sand, silt, and clay) mixed with organic matter of the deeper basins of lakes. (This is the only category of "lentic—profundal.")

Moist sand beach areas of large lakes.

Rocks, sand, and mud flats of the intertidal zone.

After Merritt, R. W., and Cummins, K. W. (1996). "An Introduction to the Aquatic Insects of North America." Kendall/Hunt, Dubuque, IA.

TABLE III Categorization of Aquatic Insect Habits: That Is, Mode of Existence

Category

Description

Skaters Adapted for "skating" on the surface where they feed as scavengers on organisms trapped in the surface film (e.g., Heteroptera: Gerridae, water striders).

Planktonic Inhabiting the open-water limnetic zone of standing waters (lentic; lakes, bogs, ponds). Representatives may float and swim about in the open water but usually exhibit a diurnal vertical migration pattern (e.g., Diptera: Chaoboridae, phantom midges) or float at the surface to obtain oxygen and food, diving when alarmed (e.g., Diptera: Culicidae, mosquitoes).

Divers Adapted for swimming by "rowing" with the hind legs in lentic habitats and lotic pools. Representatives come to the surface to obtain oxygen, dive and swim when feeding or alarmed; may cling to or crawl on submerged objects such as vascular plants (e.g., Heteroptera: Corixidae, water boatman; Coleoptera: adult Dytiscidae, predaceous diving beetles).

Swimmers Adapted for "fishlike" swimming in lotic or lentic habitats. Individuals usually cling to submerged objects, such as rocks (lotic riffles) or vascular plants (lentic) between short bursts of swimming (e.g., Ephemeroptera: Siphlonuridae, Leptophlebiidae).

Clingers Representatives have behavioral (e.g., fixed retreat construction) and morphological (e.g., long, curved tarsal claws, dorsoventral flattening, ventral gills arranged as a sucker) adaptations for attachment to surfaces in stream riffles and wave-swept rocky littoral zones of lakes (e.g., Ephemeroptera: Heptageniidae; Trichoptera: Hydropsychidae; Diptera: Blephariceridae).

Sprawlers Inhabiting the surface of floating leaves of vascular hydrophytes or fine sediments, usually with modifications for staying on top of the substrate and maintaining the respiratory surfaces free of silt (e.g., Ephemeroptera: Caenidae; Odonata: Libellulidae).

Climbers Adapted for living on vascular hydrophytes or detrital debris (e.g., overhanging branches, roots and vegetation along streams, submerged brush in lakes) with modifications for moving vertically on stem-type surfaces (e.g., Odonata: Aeshnidae).

Burrowers Inhabiting the fine sediments of streams (pools) and lakes. Some construct discrete burrows that may have sand grain tubes extending above the surface of the substrate or the individuals may ingest their way through the sediments (e.g., Ephemeroptera: Ephemeridae, burrowing mayflies; Diptera: most Chironominae, Chironomini, bloodworm midges). Some burrow (tunnel) into plants stems, leaves, or roots (miners).

After Merritt, R. W., and Cummins, K. W. (1996). "An Introduction to the Aquatic Insects of North America." Kendall/Hunt, Dubuque, IA.

TABLE IV General Classification Systems for Aquatic Insect Trophic Relations

Subdivision of function group

Functional --General particle size group" Dominant food Feeding mechanism Examples of taxa range of food (|!m)

Subdivision of function group

Functional --General particle size group" Dominant food Feeding mechanism Examples of taxa range of food (|!m)

Shredders

Living vascular hydrophyte

Herbivores—chewers

Trichoptera:

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