Natural Disturbances Flashcards
Physiological Tolerance to the Abiotic Environment
Determines where a species can be found, and under which conditions successful breeding will occur
Water Movement
Most easily identifiable in rivers and coastal seas (with solid substratum) // Might be seen as harsh environments, but aquatic organisms rely upon water mobility
Physical Disturbances
Are defined relatively, where abnormally larger currents would be a disturbance, or where a ice scour is something species are adapted to in polar regions and thus not a disturbance
Biological Disturbances
For example, predation or an outbreak of parasitism
Biotic Interactions
The primary determinants of gross community structure in ecological systems
Biotic Interactions in Aquatic Systems
The effects of predation and competition are important components, yet are tempered by the underlying abiotic (and particularly physical) environment // ALSO the physical environment creates heterogeneity and disturbance across the range of spatial and temporal scales
Drift (in rivers)
Individuals of normally benthic species suspended in the water column and being carried downstream by the current
Nocturnal Increase in Drift
A technique to avoid increased predation from being suspended in the water column, since predators can’t see as well
Catastrophic Drift
Could be caused by floods or other adverse events like the input of a pollutant
Floodplain
The velocity of water is reduced in the floodplain, and organisms can be re-deposited here
Hyporheic Zone
A layer of saturated sediments and subsurface water beneath the river channel, may be a refuge during floods/high flow
River Channel
Dead zones of flow may occur, where the flow is low enough for vulnerable benthic or swimming species to persist
Scales of Refugia
Often at the microhabitat scale, such as within a river stretch, yet may also occur between-habitats, particularly for species with complex life cycles
Drought
Direct effects, like shallower pools, disjointed rivers, and increased population density as well as indirect effects, like higher water temperatures and deoxygenation, siltation, and high nutrient levels
Disturbance-Dominated Communities
Composed of species among which there are no influential interactions, because physical disturbance is so intense and frequent
Competitive Communities
Those governed by a resource which is both limiting and patchily distributed // the first species to colonize a patch may dominate in founder control, or species with slightly different requirements will partition the resource in partitioning competitive communities
Predation-Structured Communities
The activity of predators has a significant impact on the numbers of their prey (positive and negative impacts for different populations of the community)
What is the nature of many dominant species in stream systems?
Many are omnivores, and trophic levels are often poorly defined
What is the major determinant in low-stress environments of disturbance?
Predation will be able to dominate
Bioturbation
Local-scale biological disturbance that is the result of species living within the sediment, ingesting and egesting particles or drawing oxygen-rich water down to the depths
Disturbance (general definition)
Any discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substratum availability, or the physical environment
Why is disturbance important?
It is one of the MOST important ecological processes in the maintenance of diversity by opening up resources for colonization by opportunistic species
Intermediate Disturbance Hypothesis
Describes the response of community diversity across gradients of disturbance, with highest diversity occurring at intermediate levels of disturbance, where both opportunistic and climax species flourish
Temporal Duration of Disturbance
Pulse (e.g. cyclone or storm), Press (e.g. land reclamation or spoil disposal), Ramp (e.g. climate change)
Community Stability
Ability of a community to maintain its structure during a disturbance
Resistance
Degree of change in community structure (high resistance if little change // low resistance if much change)
Resilience
Amount of time it takes for a community to return to normal
Alternative Stable States
If a community can’t return to original state, it’s replaced by a new community structure better resistant to change
Dynamic Equilibrium Model
Only strong disturbances can counteract effects of high competition
Spate
Rapid and sudden increase in flow rate, aka flooding // can impact benthic sediment and composition, and biota in all levels of water column
Direct Results of Drought
Reduced runoff, reduced soil moisture, reduced water levels, reduced stream flow
Impacts of Drought
Reductions in habitat space for obligate aquatic fauna, increase in habitat fragmentation, decrease in water quality, increase in water temperature, hypoxia, and salinity (for estuaries)
Flow Refuges
floodplains, hyporheric zone, stream channel
what does the effect of an extreme flow depend on
magnitude of flow, refuge availability, stream morphology, species traits
