8142

• UCREFRP Catalog Number: 8142
• Author: Horn, M. J.
• Title: Nutritional Limitation of Recruitment in the Razorback Sucker ‎(
• USFW Year: 1996.
• Copyright Material: NO

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CHAPTER 1. OVERVIEW AND STATEMENT OF THE PROBLEM

I. Introduction

1. General Review

Alteration and destruction of natural ecosystems are resulting from ever-

increasing human demands on the global environment (Brossard 1991; Lubchenco et al.

1991). The planet is no longer comprised of a series of pristine ecological systems, but

of systems artificialized in one way or another by human technology, some more

significantly than others (Pimm 1986). Human actions superimpose pervasive, continual

perturbation on natural disturbance regimes that maintain habitats and biotic communities

(Stanford et al. 1995). The result is suppression and loss of environmental heterogeneity

and a reduction in the productive abilities of biotic resources. Extinction rates have

increased, almost exponentially as a result of such actions (Myers 1986). Declines and

disappearances of species are correlated with physical alterations such as loss of breeding

sites, changes in habitat quality such as shifts of food availability or timing of abiotic

events, and changes in biotic pressures due to range extensions and introductions of

species better adapted to new conditions.

Life histories of species represent unique evolutionary solutions to age- or size-

specific patterns of survivorship (Tanner 1966, 1971; Wilbur et al. 1974; Southwood

1977; Reznick and Endler 1982). Species with broad tolerances, adjustable reproductive

strategies, and opportunistic tendencies may thus persist and even increase in the face of

change (Angermier 1985). Those with more constrained life history requirements will

likely decline, particularly when changes impinge on critical life-history stages (Boesch et

al. 1976; Poffand Ward 1990). Extinction may result when disturbance exceeds the limits

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