The movement of individuals is foundational to many ecological processes. For example, the movement of an organism from one place to another alters population density at both sites and has potential for affecting the genetic dynamics within the new population. Individual movement events may be in synchrony with overall trends in populations, e.g. spawning migrations, or may be atypical (asynchronous). This latter movement type can affect population and metapopulation dynamics, depending on its prevalence within a population. Nevertheless, given the complexity of interactions, the causative factors of movement are understood vaguely, much less for aquatic organisms. Drivers of movement are extrinsic (e.g. habitat quality, predation or habitat heterogeneity) and intrinsic (e.g. sex, size, or behavioral tendencies). Interactions among these drivers provide crucial insight into the patterns of movement observed within populations. Habitat is here shown to affect observed movement patterns of populations of southern leatherside chub (Lepidomeda aliciae). Streams with higher-quality habitat were inhabited by populations exhibiting lower overall movement compared to lower-quality streams. However, observations of individual long distance movement relative to the norm within the population suggest that movement may also be behaviorally based. In further tests, it is shown that, indeed, behavioral tendencies of individuals can be measured and are predictive of annual movement by individuals. Other drivers, habitat availability and quality, were also found to influence movement on a yearly basis. Movement patterns are also affected by the presence or absence of predators. A tropical livebearer (Brachyrhaphis rhabdophora) has a higher percentage of individuals classified as generally moving when predators are absent from the environment compared to predator sites. Predation environment also significantly affects individual body shape with predator sites possessing caudal peduncles with greater surface area, an adaptation likely promoting burst speed for greater escape abilities. Classification of individuals as generally moving or generally not moving was also significantly related to variation of body shape of these fish. However, biological significance is ambiguous given the absence of obvious morphology trends explained by this factor. It is critical to understand these drivers to better understand the dynamic interface between ecology and evolution.

The Staunton River is a high gradient, second order stream approximately 6 km in length located on the eastern slope of the Blue Ridge Mountains in Shenandoah National Park, VA. In June 1995, a catastrophic flood and debris flow altered the instream habitat and <i>Salvelinus fontinalis</i> population of the Staunton River. The debris flow scoured the streambed, deposited new substrate materials, removed trees from the riparian zone, and eliminated fish from a 1.9km section of the stream. By June 1998, both young-of-year (YOY) and age 1+ <i>S. fontinalis</i> had recolonized the debris flow affected area. The event provided a rare opportunity to examine recovery of the <i>S. fontinalis</i> population and instream habitat in addition to addressing potential effects of the debris flow on movement, activity, and growth of fish in the debris flow affected and unaffected areas of the stream. Post-recolonization movement and activity were monitored using two-way fish traps (weirs), mark-recapture techniques, and radio telemetry. The weirs failed to produce any movement data. Most fish (91%) in the mark-recapture study had range sizes less than 100m, however biases common to mark-recapture study designs (low recapture rate, flawed logic, etc.) hampered interpretation of results. For example, subsequent recapture of individually marked fish indicated that as many as 54% of marked fish confirmed to have been alive at the time of a recapture session were not recaptured. Radio telemetry provided information on <i>S. fontinalis</i> movement and activity at seasonal and diel scales during summer and fall. Differences in movement and activity between the debris flow affected and unaffected areas were minimal when compared to seasonal variations. During summer, range sizes were near 0m and crepuscular activity patterns were observed. During the fall range size increased and diel activity was concentrated in the mid-afternoon with a much higher peak than during summer. Basin-wide visual estimation technique (BVET) fish population surveys performed each spring and fall from 1993 = 1999 provided pre- and post-event fish population abundance and density estimates. Post-event fish growth in the debris flow affected and unaffected areas was monitored using mark-recapture techniques. Abundance and density of both YOY and age 1+ <i>S. fontinalis</i> exceeded pre-event levels within 2-3 years. Growth of YOY and age 1+ fish was significantly greater in the debris flow affected area until spring 1999. Population density appeared to have a strong negative influence on growth. The observed changes in fish growth and differences in fish size associated with population density would be of minimal importance to the typical angler but may suggest a mechanism by which <i>S. fontinalis</i> populations can quickly recover from catastrophic events. BVET habitat surveys provided information on total stream area, number of pools and riffles, pool and riffle surface area and depth, substrate composition, and large woody debris (LWD) before (1993), immediately following (1995), and four years post-event (1999). Immediately following the debris flow, the stream channel was highly disordered which resulted in an increase in the total number of habitat units and a decrease in average habitat unit surface area, total stream area, and average depth when compared with pre-event conditions. In addition, substrate composition had shifted from small to large diameter particles and LWD loading had increased in both debris flow affected and unaffected areas. Four years after the event, the total number of habitat units, average habitat unit surface area, total stream area, and average depth had all returned to near pre-debris flow levels and substrate composition had begun to shift towards smaller particle sizes. Changes in LWD loading from 1995-1999 reflected changes in the riparian zone following the debris flow. In the unaffected area, where riparian trees remained intact, LWD loading increased, whereas in the debris flow affected area, where riparian trees were eliminated, LWD loading decreased. For the most part the effects of the debris flow, although immediately dramatic, were in the long term minimal. The debris flow affected area was recolonized rapidly and abundance and density quickly rebounded past pre-event levels. Differences in fish growth between the affected and unaffected area were short lived. Any effect the debris flow affected area may have had on movement or activity was minimal when compared with seasonal variations. Most habitat characteristics reverted to near pre-event levels just four years after the flood and debris flow. Although a number of factors will influence recovery time from such events, these results indicate that immediate management action, such as stocking or habitat modifications, are not necessary in all cases. / Master of Science

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal