Digital Commons Network^™

Ecological Changes Of The Lower Niobrara River Valley And Lewis And Clark Lake Delta From Past To Present, Madalyn Christine Bollig

Dissertations and Theses

Over half of the world’s large river systems are impacted by dams. These may prevent sediment flow downstream, resulting in accumulation in the upstream reservoir. On the Missouri River, deltas and associated backwater-affected areas occur in nine locations across six reservoirs. One of these, the Lewis and Clark Lake delta-backwater, is influenced by sediment inputs from both the Missouri River and the Niobrara River. While the extension of the prograding delta into the reservoir has been well documented, there has been little research on upstream (backwater) effects of the delta on the lower Niobrara River. This study examined ecological changes …

Woodpeckers In The City: Habitat Use And Minimum Area Requirements Of Woodpeckers In Urban Parks And Natural Areas In Portland, Oregon, Adam Baz

Dissertations and Theses

Urbanization has contributed to the fragmentation and alteration of natural habitats around the globe, and is rapidly increasing. In this context, forested parks play a critical role for many species by providing patches of usable habitat within the urban matrix. Such patches may be particularly valuable to forest-specialists like woodpeckers (Picidae). Yet many woodpeckers require large forest patches, which are limited in fragmented landscapes. Despite their recognized value as ecosystem engineers and keystone species, almost no research exists on woodpecker ecology or space-use in urban settings. What habitat components influence woodpecker abundance and what are their functional minimum area requirements …

Methodological Advancements For Improving Performance And Generating Ensemble Ecological Niche Models, Robert Boria

Dissertations and Theses

This study employs spatial filtering of occurrence data with the aim of reducing overfitting to sampling bias in ecological niche models (ENMs). Sampling bias in geographic space leads to localities that may also be biased in environmental space. If so, the model can overfit to those biases. As a preliminary test addressing this issue, we used Maxent, bioclimatic variables, and occurrence localities of a broadly distributed Malagasy tenrec, Microgale cowani (Family Tenrecidae: Subfamily Oryzorictinae). We modeled the abiotically suitable area of this species using three distinct datasets: unfiltered, spatially filtered, and rarefied unfiltered localities. To quantify overfitting and model performance, …

Interception In Open-Grown Douglas-Fir (Pseudotsuga Menziesii) Urban Canopy, Mitchell Bixby

Dissertations and Theses

I hypothesized that Douglas-fir trees (Pseudotsuga menziesii) standing apart from other trees ('open-grown') will intercept more rainfall than Douglas-fir trees standing near other trees ('closed-canopy'). Open-grown trees differ structurally and are more common in urban settings, yet have been infrequently studied. Existing literature, based primarily on closed-canopy trees, suggests Douglas-fir trees in Pacific Northwest forests intercept approximately 25% of rainfall annually. Because open-grown trees have more vertical leaf area than individual trees in closed-canopy forests, I expected to find higher interception by open-grown trees.

I collected throughfall under four open-grown Douglas-firs using six static collectors ('buckets') per tree, …