Biology: Habitats

Aquatic Habitat

Several life forms spend most, if not all, of their lives in aquatic ecosystems. These aquatic organisms include types of bacteria, algae, plants, zooplankton, crayfish, insects, mussels, fish, amphibians, reptiles, and mammals. The diversity of aquatic organisms depends on the variety of aquatic habitats.

1. A sinuous stream provides more habitats than a straight channel.
2. A streambed composed of rocks and sediment of many sizes provides a greater assortment of habitats than a streambed of uniform sediment.
3. Lakes with natural shorelines and clear water provide more habitats than highly altered, turbid lakes.

Streams include an added degree of habitat and biological diversity along a longitudinal gradient, from the headwaters to the lower reaches. The River Continuum Concept describes how the structure of the stream and its biological communities evolve along the length of the river. In general, as the size of the stream grows, so does the diversity of habitat, invertebrates, and fish.

Shallow lakes are another example of a productive system with a continuum of habitat types. High nutrient content (phosphorus, nitrogen, and minerals) together with the sunlight available through shallow water, leads to abundant aquatic plant life. Stands of emergent and floating-leaved plants such as cattails, bulrush, and water lily, as well as submerged plants such as coontail, create an extensive littoral zone. These plants provide excellent food and habitat for a variety of animal life, and also anchor sediments, maintaining water clarity (Conroy 2005). Shallow lakes are well recognized as important as breeding areas for waterfowl species, such as the lesser scaup, northern pintail, and common moorhen.

Terrestrial, Riparian Habitats

Terrestrial plants around a lake, along the stream, in the floodplain, and in the valley are vital to the character of these aquatic habitats. The pattern of vegetation along a stream corridor or around a lake will depend on climate; disturbance such as flood, erosion, and fire; formation of floodplains; soil type; and soil moisture.

Plant communities form a mosaic, depending on conditions along the stream and in the floodplain. The disturbance of periodic floods provides an opportunity for new plant growth. For example, plains cottonwood, black willow, and silver maple are adapted to taking root in recently deposited sediments. Because these species are able to withstand deposition of sediment and scouring that exposes their root systems, they can outcompete other tree species in a floodplain environment.

Clearing stream or lakeside riparian vegetation for lawns has a detrimental effect on the biotic systems.

Shoreline plants are important sources of shade and energy. Throughout a stream’s length and around a lake, the vegetation along the riparian corridor intercepts flows of incoming runoff, nutrients and contaminants. Plants are critical components of nitrogen, carbon, and oxygen cycles—serving as production sites and conversion centers for life-sustaining elements. A biologically diverse plant community is more resilient to disturbances and disease than simplified communities or monocultures (Tilman et al., 1996); (Tilman et al., 1997). Deep-rooted native plants anchor soil in place and stabilize streambanks. Plants at the water’s edge also serve as buffers from bank erosion, absorbing the energy of lapping waves and swift currents. The proportion of vegetation to paved surfaces throughout a watershed is an important factor in the water quality of that watershed.

A mosaic of terrestrial plant communities provides more diverse habitats that support more diverse animal communities than homogeneous plant communities, such as cornfields. Fens, marshes, floodplain forests, outwash plains, oxbow lakes, side channels, mudflats, shrub swamps, sand prairies and wet meadows are examples of habitats that support a rich diversity of life. The physical structure of the habitat in large part determines habitat quality.

Corridors

Because many animals require both upland and aquatic habitats for their life cycles, it is essential to keep these physical habitats connected. It is important to also protect habitats along lateral and longitudinal gradients to allow movement of migrating and traveling wildlife. Long wooded stream courses provide many species, especially mammals, important avenues of movement to other habitats. Larger river corridors are major continental flyways for migrating birds.

The existence of streams, lakes, and wetlands becomes especially important in altered and developed landscapes. In urban and agricultural areas, the floodplain of a river is sometimes the only stretch of remaining native habitat for birds, mammals, amphibians, reptiles and invertebrates. Under such circumstances, the wooded streamside may have the best or only available cover for large mammals, such as fox, raccoon, and deer. More about the importance of landscape connectivity and corridors can be found in Connectivity Concepts.

The Minnesota River Valley as an example of an important corridor of native plant communities that lies within an mainly agricultural or urban part of Minnesota. This corridor supports some of the state’s rarest plant species and noteworthy concentrations of animals. The natural corridors created by the steep topography of southeastern Minnesota are home to some of the state’s rarest reptiles and amphibians. The Timber rattlesnake and the five-lined skink are examples of remnant populations dependent on unique habitats associated with these steep bluffs and wooded valleys.

Endangered, Threatened, and Species of Special Concern

A species is considered endangered if the species is threatened with extinction throughout all or a significant portion of its range within Minnesota.

A species is considered threatened if the species is likely to become endangered within the foreseeable future throughout all or a significant portion of its range within Minnesota.

A species is considered a species of special concern if, although the species is not endangered or threatened, it is extremely uncommon in Minnesota, or has unique or highly specific habitat requirements and deserves careful monitoring of its status. Species on the periphery of their range that are not listed as threatened may be included in this category along with those species that were once threatened or endangered but now have increasing or protected, stable populations. For more information see the MN DNR’s Endangered, threatened, and special concern species webpage at https://www.dnr.state.mn.us/ets/index.html.

Species in Greatest Conservation Need (SGCN)

Species in greatest conservation need (SGCN) are defined as native animals whose populations are rare, declining, or vulnerable to decline and are below levels desirable to ensure their long-term health and stability. The MN Wildlife Action Plan 2015-2025 is a strategic plan the addresses the primary causes of species population declines: habitat loss, degradation and fragmentation, non-habitat issues (low reproduction, poor dispersal ability, disease) and climate change impacts.  In Minnesota 346 species meet the definition of species in greatest conservation need. These species includes mammals, birds, reptiles, amphibians, fishes, insects, and mollusks, and represent about sixteen percent of the greater than 2100 known native animals in Minnesota.

For example, within the vertebrate groups, one-quarter to over half of the total number of species are species in greatest conservation need. More information and complete species lists are available here.