Academic journal article Environmental Law

Migratory Species and Ecological Processes

Academic journal article Environmental Law

Migratory Species and Ecological Processes

Article excerpt

     A. Ecosystem Services of Migratory Species
     B. Negative Effects of Migratory Species
     A. Serengeti Ungulates
     B. Pacific Salmon
     C. Long-Nosed Bats and Hummingbirds
     D. Manatees
     E. Migratory Birds
IV.  Conclusion


Migration of animal species, defined as the periodic movement between two sites, (1) has been well recognized for millennia and subject to intense scientific interest for over 150 years. Most scientific attention has been focused on the physiology, behavior, or population dynamics of particular migratory species. (2) Yet like all species, migratory species are members of ecological systems (ecosystems)--assemblages of plants, animals, and microbes that interact with one another and with the physical and chemical environment. The capture and transformation of energy and nutrients by organisms within ecosystems, through photosynthesis, nitrogen fixation, feeding, defecation, pollination, and decomposition among myriad other processes and activities, results in an array of life-supporting goods and services without which human life could not be sustained. (3) Food, fiber, and timber production; recreational and aesthetic experiences; the provision of life-saving drugs and other pharmaceuticals; and the supply of fresh air and water are just a few of the ecosystem services provided by nature's "green infrastructure." (4) The activities of organisms in ecosystems can also result in disservices to humans, such as sustaining and spreading pests and disease.

From this ecological perspective, migratory species are of interest as components of two or more ecosystems and vectors for energy and matter transfer between them. The distance and frequency that migratory species travel in space and time can vary widely, from the diurnal movements of tiny krill (e.g., Euphausia superba) through a few hundred vertical feet of ocean water (5) to the annual circumpolar navigations of Arctic Terns (Sterna paradisaea). (6) Despite these differences in scale, all migratory species share the distinction of being regular participants in multiple ecosystems encountered throughout the migration route.

An important rationale for the conservation of species, including migratory species, is rarity. Rare species are more likely to go extinct because of demographic fluctuations or loss of critical habitat. (7) However, the ecosystem services provided by species may be a positive function of their abundance, such that the greater the number of individuals the greater amount of ecosystem services they provide. (8) Animal migrations provide especially clear examples of this relationship because they are often phenomena of abundance (9) and their periodic and often discrete nature facilitates measurement of species effects. For example, the more salmon migrate upstream to their spawning grounds, the more marine nutrients are transported inland to fertilize stream and forest ecosystems. (10) Likewise, the larger a population of migratory pollinators, the more plants will be pollinated. (11) Thus, valuation of migratory species based on their capacity to provide ecosystem services may be the inverse of their valuation based on rarity. This represents an alternative paradigm to rarity-based conservation and instead provides a strong rationale for conserving and protecting abundant migratory species because of the magnitude of their ecosystem services.

Using the framework of ecosystem services and disservices our focus here is to consider the functional roles of migratory species as members of multiple ecosystems and to highlight novel implications for conservation policy that arise from this functional perspective. In Part II, we discuss the Millennium Ecosystem Assessment framework for ecosystem services and provide examples of the ecosystem services and disservices of migrating species. In Part III, we present case studies in order to explore more fully the services and disservices of migratory species and their relationship to abundance. …

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