The biggest example, as mentioned before, is to drift at night. Avoidance Ĭommon invertebrate species have adapted drifting behaviors to help avoid predation. įish predation on invertebrate has been seen to alter prey densities in streams by individual feeding of insects or by effecting insect dispersal behavior. As such, sculpins were found to catch a majority of their prey at night, as well as during the day. Other fish, such as the sculpin, have evolved with highly developed lateral lines, allowing them have better nocturnal predation skills. This has led to studies concluding that many invertebrate have adapted to drifting at night, where they can avoid predation due to these fish being mainly visual hunters. These fish catch a lot of their prey during dusk and dawn. The most common example of drift-feeding predators are stream salmonids, especially trout. Sculpin are bottom feeders that look for insects drifting near the substrate Predators that use this as their main source for food, typically fish, are called drift-feeders. Many of these predators have adapted or have become specialized to feeding on invertebrates found in stream drift. Many predators of common insects and invertebrates found in streams feed off of those found in stream drift. Müller (1954) found that water mites ( Hydracarina) and aquatic beetles ( Coleoptera) made up a large portion of the benthos population in the stream Skravelbäcken of Sweden, but since they associated with boulders and thick plant growth, they avoid being dislodged by water currents into drift. An example of the friction disk can be seen on the image to the right which shows the ventral side of a species within the genus epeorus.
Larvae within the genus have modified gills forming a friction disc that allows them to cling to the substrate in rapid moving waters. An example of the former is the family Heptageniidae in the order Ephemeroptera.
Invertebrate species adapt to a stream’s current through the organs or appendages that physically attach them to the substrate, or association with large boulders or thick plant growth to buffer the disturbances associated with flow. Surface Drift: Adult insects drift as they emerge on the surface of the river and drift when adult insects return to the surface to lay eggs.Emergence Drift: Nymphs and pupae drift as they swim to the surface to emerge into their adult stage.
Constant Drift: Also known as Background Drift, describes a low, consistent rate of drifting invertebrates between temporal peaks.Distributional Drift: Used by animals to disperse progeny downstream.Active drift describes animals choosing to enter drift. Behavioral Drift: Behavior such as escaping, and inadvertently losing foothold in the water column, cause animals to drift downstream.Catastrophic Drift: Disturbances such as floods physically dislodge animals.Invertebrate Drift can be categorized by the conditions that caused the drift to occur. 1.4 Environmental Factors Affecting Invertebrate Drift.Drift has been documented to impact community structure, benthic production, and the energy flow through trophic levels. The study of invertebrate drift has progressed the field of stream ecology. From it, research as far back as 1928 has collected data on the phenomenon of drift. Researchers have developed sampling techniques in lotic systems. Fishermen can exploit this relationship using fly fishing techniques and lures that mimic drifting insects to catch these fishes. Species of fish, commonly salmonids, catch drifting insects during the peak times after dusk, and before dawn. And just as invertebrates adapted to stabilize themselves in the water column, or use the stream’s energy to their advantage, so too have predators adapted to catch invertebrates as they drift. For that, invertebrates counter a stream’s flow through physical and behavioral adaptations. On occasion, however, invertebrates will inadvertently lose their footing, and drift downstream. ĭrift can service freshwater invertebrates by giving them an escape route from predation, or the use of a current to disperse progeny downstream. This is in contrast with lentic coming from the Latin word lentus, meaning slow or motionless that typically describe still or standing waters such as lakes, ponds, and swamps. The term lotic comes from the Latin word lotus, meaning washing, and is used to describe moving freshwater systems. Invertebrate drift is the downstream transport of invertebrate organisms in lotic freshwater systems such as rivers and streams. Downstream transport of invertebrate organisms in rivers and streams
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