| Riverine ecosystems are inherently dynamic and are being increasingly altered by anthropogenic activities. To address the effects of anthropogenic alterations, ecologists need to understand how species are influenced by current habitat conditions at diel, seasonal, and annual temporal scales. In temperate rivers, climate change is projected to increase water temperatures, reduce the duration of ice cover, and cause spring runoff to occur earlier and with lower magnitude. At the diel scale, formation of surface ice cover eliminates daily temperature cycles (0-6° C) and creates stable conditions near 0° C. To understand the energetic effects of temperature changes associated with ice cover, I compared fish energy use among cycling (0-6° C), stable mean (3° C) and stable minimum (0° C) temperatures. Stable temperatures created by ice cover did not provide energetic benefits over the cycling temperatures and the loss of energy reserves declined at similar rates among temperature regimes. At the seasonal scale, ice cover potentially provides protection for fish from endothermic predators. To understand the effects of ice cover on fish behavior, I compared fish activity during periods with and without ice cover using underwater videography. Ice cover did not change fish behavior patterns and fish remained more active in backwater habitats than main channel habitats during both ice free and ice cover periods. At the annual scale, spring runoff is the primary form of disturbance that structures fish habitat. To understand how habitat patches change with disturbance I compared the abundance and total area of macrophyte, wood, and deep water patches to maximum discharges using habitat mapping and simulation models. The abundance and area of macrophyte patches were negatively correlated with disturbance, whereas the abundance and area of both wood and deep water patches were positively correlated with disturbance. Understanding current fish-habitat relationships at three temporal scales indicates that shifts in diel temperature regimes during winter will not have energetic consequences for fish and that backwaters are important winter habitats. Decreased spring flood magnitudes will result in shifts in the composition of fish habitats and it is necessary to understand how different species will respond to these changes. |
