Density-Dependent Processes in the Life History of Fishes: Evidence from Laboratory Populations of Zebrafish Danio rerio

Charles R E Hazlerigg,Charles R Tyler,James R Wheeler,Kai Lorenzen,Pernille Thorbek,Stuart A Sandin

doi:10.1371/journal.pone.0037550

Abstract

Population regulation is fundamental to the long-term persistence of populations and their responses to harvesting, habitat modification, and exposure to toxic chemicals. In fish and other organisms with complex life histories, regulation may involve density dependence in different life-stages and vital rates. We studied density dependence in body growth and mortality through the life-cycle of laboratory populations of zebrafish Danio rerio. When feed input was held constant at population-level (leading to resource limitation), body growth was strongly density-dependent in the late juvenile and adult phases of the life-cycle. Density dependence in mortality was strong during the early juvenile phase but declined thereafter and virtually ceased prior to maturation. Provision of feed in proportion to individual requirements (easing resource limitation) removed density dependence in growth and substantially reduced density dependence in mortality, thus indicating that ‘bottom-up’ effects act on growth as well as mortality, but most strongly on growth. Both growth and mortality played an important role in population regulation, with density-dependent growth having the greater impact on population biomass while mortality had the greatest impact on numbers. We demonstrate a clear ontogenic pattern of change in density-dependent processes within populations of a very small (maximum length 5 mm) fish, maintained in constant homogeneous laboratory conditions. The patterns are consistent with those distilled from studies on wild fish populations, indicating the presence of broad ontogenic patterns in density-dependent processes that are invariant to maximum body size and hold in homogeneous laboratory, as well as complex natural environments.

Highlights

Fundamental to the long-term persistence of populations is their adjustment and regulation in response to harvesting, habitat modification, and exposure to chemicals [1,2,3]
Regulation is effected through density dependence in life history characteristics, and may result from intraspecific competition, predation or parasitism which may vary in intensity throughout the life-cycle [4,5]
Munch et al [14] hypothesize that bottom-up processes of regulation are likely to act in later phases of the life-cycle while top-down processes are most important at early life-stages

Summary

Introduction

Fundamental to the long-term persistence of populations is their adjustment and regulation in response to harvesting, habitat modification, and exposure to chemicals [1,2,3]. Fish and many aquatic invertebrates have complex life histories with stages that differ greatly in size, morphology, and ecological requirements and which may occupy different habitats. These lifestages differ in the degree to which they are subject to density dependence and in the life history traits (features of survivorship, growth, development and reproduction) most affected. Recent research indicates that density dependence in other life history traits and phases of the life-cycle, in particular density-dependent body growth in juveniles and adults, can be important and add substantially to the compensatory reserve of fish populations [2,12,13]. There is, increasing empirical evidence and theoretical support for the importance of multiple densitydependent processes, acting at different stages of the life-cycle, in the regulation of fish populations

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