8) Urbanization may lead to ecological homogenization across cities in different

Question

8) Urbanization may lead to ecological homogenization across cities in different regions (recall Groffman et al. 2014 and the class exercise regarding that paper). If true, urban systems in different regions should be quite ecologically similar to each other while native ecosystems in the same regions should be quite different from one another. NOTE: You need to answer Part A and Part B Part A - Briefly explain the rationale behind this 'homogenization hypothesis'. and Part B - Design a study to test the homogenization hypothesis in New Zealand. Incorporate specific and appropriate ecological metrics and processes for terrestrial and aquatic systems in your study design. Consider also the drivers of those ecological factors in your design.

Explanation / Answer

PART A.

Urban ecosystems are widely hypothesized to be more ecologically homogeneous than natural ecosystems. We argue that urban plant communities assemble from a complex mix of horticultural and regional species pools, and evaluate the homogenization hypothesis by comparing cultivated and spontaneously occurring urban vegetation to natural area vegetation.. There was limited support for homogenization of urban diversity, as the cultivated and spontaneous yard flora had greater numbers of species than natural areas, and cultivated phylogenetic diversity was also greater. However, urban yards showed evidence of homogenization of composition and structure.Despite increasing urbanization, its potential impacts on community assembly of organisms, biodiversity, and ecosystem function are unclear—urban ecosystems were the least-studied in a recent review of over 11,500 assemblages. Compounding this uncertainty, any urban flora includes both human-cultivated and spontaneously occurring species, each of which is subject to distinct ecological and human influences.

The horticultural flora is influenced by accessibility of plant material, propagation constraints, and human preferences and is further filtered by regulation and management processes. In contrast, the naturally assembled continental and regional floras are influenced by historical biogeographic processes and filtered by climate, pollution, soil, and other abiotic constraints. Similarly, cultivated and spontaneous pools within the regional and urban flora are also subject to contrasting dispersal and filtering processes within the urban environment.

we examine three components of urban vegetation—diversity, composition, and structure—and hypothesize how each might vary across the species pools we outline in our framework . The major cities of North America span broad environmental gradients of temperature, precipitation, light availability, and many other factors. We focus here on water stress , which is a major axis across which our seven cities are relatively evenly spread. Moreover, it can be quantified as a composite of both temperature and precipitation , unifying two major axes of variation in one biologically meaningful variable.

Diversity- Human transport and management of vegetation enables cultivated species to overcome natural dispersal and establishment barriers, such that we expect the species richness of the cultivated pool to be higher than that of urban spontaneous or nearby natural pools. Plant species richness of all species pools should positively correlate with moisture availability, consistent with well-established relationships between species richness and climate.

Composition- If climate is a strong filter on the composition of spontaneous and natural area species pools, we would expect the species and phylogenetic clades of pools to vary across regions. Within regions, however, these pools are drawn from the regional flora and are subject to the same climate filters, so we expect some compositional similarity within regions. By contrast, if human preferences, transport, or management relaxes the constraints imposed by climate and dispersal barriers, we expect cultivated pools to be homogenized:

Structure -Given similar human preferences and management to mitigate climatic constraints , we expect cultivated pools to have similar structures—as measured by tree height and density—across regions. By contrast, we suggest climate filters will lead to divergence in the structure of natural area pools, with taller trees and greater tree density in wetter regions.

In describing homogenization, we focus on urban cultivated and spontaneous species pools in relation to natural area pools. Homogenization might be seen as a reduction in the number of lineages represented in urban areas, more similar species compositions, or lesser variation across urban areas in structural aspects of the vegetation such as overall density and height of vegetation.

PART B.

Understanding Ecosystem Terminology

Ecology is a scientific field that studies the relationships between and among (micro)organisms such as plants, animals, and bacteria and their environment. Like most scientists, ecologists use a variety of terms to describe aspects of their discipline.Ecosystem biodiversity describes a number and kinds of organisms in a specific geographic area that can be distinguished from other areas by its physical boundaries (e.g., lake, forest), though such boundaries can be somewhat arbitrary.

Ecosystem structure refers to both the composition of the ecosystem and the physical and biological organization defining how those parts are organized. A leopard frog or a marsh plant such as a cattail, for example, would be considered a component of an aquatic ecosystem and hence part of its structure.

attempts to develop explicit maps of the linkage between aquatic ecosystem structure/function and value should be made.information about water quality standards, detailed summaries of the results of waterbody assessments by designated uses and states, and a discussion of the data collection and analysis methods should be used.

Restoring habitat and native species should be also a priority.regional homogenization occurs chiefly through modification of the magnitude and timing of ecologically critical high and low flows. for reference rivers, no evidence for homogenization was found, despite documented changes in regional precipitation over this period.

we quantitatively test the hypothesis that dams have homogenized regionally distinct river flow regimes.

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