UVM Theses and Dissertations
Format:
Print
Author:
McDonald, Michael J.
Dept./Program:
Natural Resources
Year:
2013
Degree:
MS
Abstract:
Ecosystems are under increasing stress from anthropogenic alterations to the environment. As a result of these stressors, ecological interactions are changed creating extirpations and extinctions not just of species, but also of interspecific relationships. Many of these interactions are poorly understood and may play critical roles in shaping life history strategies. Moose (Alces alces) and black-throated blue warblers (Setophaga eaerulescens) are sympatric in parts of North America. A multi-trophic relationship between the two has been suggested because regionally, both species depend heavily on the same understory shrub species, hobblebush (Viburnum alnifolium).
I found that this relationship is important to understanding the fine scale attributes utilized in nest site selection for some understory nesting birds. Through observational field data, I found that 1) moose, through the act of winter browsing on buds and twigs, have a profound effect on the morphology of hobblebush and 2) black-throated blue warbler select nest sites based on factors largely driven by moose herbivory.
Moose browse exhibited a positive effect on the number of branches on an individual hobblebush plant. Considered collectively, a patch of hobblebush composed of individual plants with more branches per plant creates a more structurally complex microhabitat. This complexity can be measured in terms of visual obscurity within the shrub strata. Paired analyses of shrub patches within an individual black-throated blue warbler's territory illustrate selective preference for patches with more branches and greater visual obscurity.
This research describes a previously unknown multi-trophic relationship yielding new information about each species and their relationship as well as habitat use in general. I found this relationship of particular interest because although moose have recently rebounded in the area (~30 years), they likely had this effect prior to a dramatic decline in their population during the early to mid-1900s. Additionally, while these two species' ranges currently overlap, under forces of global change, they may not in the future making this a temporally unique opportunity to-learn about the nature of multitrophic interactions and habitat use.
I found that this relationship is important to understanding the fine scale attributes utilized in nest site selection for some understory nesting birds. Through observational field data, I found that 1) moose, through the act of winter browsing on buds and twigs, have a profound effect on the morphology of hobblebush and 2) black-throated blue warbler select nest sites based on factors largely driven by moose herbivory.
Moose browse exhibited a positive effect on the number of branches on an individual hobblebush plant. Considered collectively, a patch of hobblebush composed of individual plants with more branches per plant creates a more structurally complex microhabitat. This complexity can be measured in terms of visual obscurity within the shrub strata. Paired analyses of shrub patches within an individual black-throated blue warbler's territory illustrate selective preference for patches with more branches and greater visual obscurity.
This research describes a previously unknown multi-trophic relationship yielding new information about each species and their relationship as well as habitat use in general. I found this relationship of particular interest because although moose have recently rebounded in the area (~30 years), they likely had this effect prior to a dramatic decline in their population during the early to mid-1900s. Additionally, while these two species' ranges currently overlap, under forces of global change, they may not in the future making this a temporally unique opportunity to-learn about the nature of multitrophic interactions and habitat use.