An Experimental Field Study of Delayed Density Dependence in Natural Populations of Aedes albopictus

Rachael K Walsh,Charles S Apperson,Fred Gould,Caitlin Bradley,Martin Krkosek

doi:10.1371/journal.pone.0035959

Abstract

Aedes albopictus, a species known to transmit dengue and chikungunya viruses, is primarily a container-inhabiting mosquito. The potential for pathogen transmission by Ae. albopictus has increased our need to understand its ecology and population dynamics. Two parameters that we know little about are the impact of direct density-dependence and delayed density-dependence in the larval stage. The present study uses a manipulative experimental design, under field conditions, to understand the impact of delayed density dependence in a natural population of Ae. albopictus in Raleigh, North Carolina. Twenty liter buckets, divided in half prior to experimentation, placed in the field accumulated rainwater and detritus, providing oviposition and larval production sites for natural populations of Ae. albopictus. Two treatments, a larvae present and larvae absent treatment, were produced in each bucket. After five weeks all larvae were removed from both treatments and the buckets were covered with fine mesh cloth. Equal numbers of first instars were added to both treatments in every bucket. Pupae were collected daily and adults were frozen as they emerged. We found a significant impact of delayed density-dependence on larval survival, development time and adult body size in containers with high larval densities. Our results indicate that delayed density-dependence will have negative impacts on the mosquito population when larval densities are high enough to deplete accessible nutrients faster than the rate of natural food accumulation.

Highlights

In the field of population ecology, both density independent factors and density dependent factors can influence the dynamics and growth of a population [1]
There was no significant relationship between the log of estimated larval density and the difference in development time between the LP and LA treatments in a given container for either level of initial density (Figure S1)
There was a significant difference in male wing length between the LP treatment and the LA treatment for containers with 16 density (t48 = 3.54, P = 0.033)

Summary

Introduction

In the field of population ecology, both density independent factors and density dependent factors can influence the dynamics and growth of a population [1]. Density-dependent factors can impact populations by both first order feedback (direct densitydependence) and second order feedback (delayed density-dependence) [2,3,4]. First order factors have direct impacts on the current population or generation of individuals, whereas second order factors have delayed impacts on the current generation or on future generations of the population. Long-term data have provided evidence for delayed density-dependence in populations of the potato aphid, Macrosiphum euphorbiae, [14], southern pine beetle, Dendroctonus frontalis, [15], forest tent caterpillar, Malacosoma disstria, [16] and in the cohabitating common sardine, Strangomera bentincki, and populations of the anchovy, Engraulis ringens [17]

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