Local and regional controls of brook trout (Salvelinus fontinalis) metapopulation dynamics within a complex Appalachian riverscape.

摘要

Brook trout have recently become a species of conservation focus due to their unique spatial structure and restricted thermal requirements. These life history characteristics make brook trout particularly vulnerable to major biodiversity threats, such as climate change and habitat loss. For appropriate conservation actions to be taken, it is imperative to identify the scale that limits brook trout productivity. The popular view of brook trout ecology indicates that populations exist as isolated fragments within watersheds, where productivity is concentrated in small, cold tributaries. This has led to management resources being allocated towards small tributaries with a goal to enhance local habitat characteristics. However, recent evidence suggests broader spatial scales are equally important for appropriate management planning. Application of landscape ecology theory has indicated that some brook trout populations may demonstrate linked metapopulation structure, where productivity and population dynamics operate at the watershed scale. Contrasting views on the appropriate spatial scale limiting brook trout productivity must be resolved for effective conservation planning: are brook trout fragmented isolates within watersheds, limited by local resources, or are they linked metapopulations that rely on dispersal and population dynamics operating at regional scales?;The upper Shavers Fork watershed in West Virginia supports a historically productive brook trout fishery. However, numerous anthropogenic factors within this watershed have led to a drastic decline in the brook trout population. Loss of riparian vegetation and increasing temperatures due to climate change has reduced the amount of larger, more productive mainstem habitats available to supplement brook trout productivity. Additional isolation by impassible barriers (e.g. culverts perched above the stream bottom) limits the number of brook trout spawning tributaries that are well connected to high quality foraging mainstem locations. Lastly, poor buffering geology increases the susceptibility of many tributary spawning areas to acid precipitation. For my dissertation, I adopted a riverscape approach to better understand which factors limit brook trout productivity within this historically productive watershed. In particular, my dissertation is strongly focused on factors that limit brook trout use of the supplementary mainstem.;My first chapter applies multiple spatial population hypotheses to a longterm brook trout monitoring data set collected along a continuum of stream sizes. In particular, these hypotheses are based within a concept known as the abundant center hypothesis. This hypothesis predicts stronger density-dependent regulation at the core of a species distribution, while density-independent factors become the limiting mechanism with distance from the core.;The second chapter of this dissertation also used the same data set as analyzed in chapter one, but incorporated a regional analysis component to partition out the actual mechanism limiting brook trout productivity in the mainstem. Both source-sink dynamics (i.e. mass effects) and habitat limitation (i.e. thermal refugia) are equally likely factors controlling brook trout distributions within the mainstem. Therefore a series of models were ranked using information theoretic to explain brook trout densities and sizes along the core to periphery, with particular focus on the periphery.;The third chapter of this dissertation took advantage of a robust capture-mark-recapture data set within this watershed to identify the relative strength of different sources and sinks as contributors to the brook trout metapopulation. Often defining sources and sinks within a landscape is limited to a discrete categorical classification. However, identifying the habitats that provide the greatest contribution to the entire metapopulation would provide substantially greater benefit towards development of management strategies.;The fourth chapter of this dissertation was designed to model growth potential and habitat selection by brook trout within this watershed as a function of current and anticipated temperature regimes along a stream continuum. Habitat quality based on energetic potential has often been used to describe fish distributions at multiple spatial scales (i.e. microhabitat to the reach). (Abstract shortened by UMI.).