Abstract
In sexual organisms, low population density can result in mating failures and subsequently yields a low population growth rate and high chance of extinction. For species that are in tight interaction, as in host-parasitoid systems, population dynamics are primarily constrained by demographic interdependences, so that mating failures may have much more intricate consequences. Our main objective is to study the demographic consequences of parasitoid mating failures at low density and its consequences on the success of biological control. For this, we developed a deterministic host-parasitoid model with a mate-finding Allee effect, allowing to tackle interactions between the Allee effect and key determinants of host-parasitoid demography such as the distribution of parasitoid attacks and host competition. Our study shows that parasitoid mating failures at low density result in an extinction threshold and increase the domain of parasitoid deterministic extinction. When proned to mate finding difficulties, parasitoids with cyclic dynamics or low searching efficiency go extinct; parasitoids with high searching efficiency may either persist or go extinct, depending on host intraspecific competition. We show that parasitoids suitable as biocontrol agents for their ability to reduce host populations are particularly likely to suffer from mate-finding Allee effects. This study highlights novel perspectives for understanding of the dynamics observed in natural host-parasitoid systems and improving the success of parasitoid introductions.
Highlights
Since the pioneering work of Nicholson and Bailey [1], many theoretical ecologists have been interested in modeling the tight interactions that occur between insect parasitoids and their hosts [2,3]
Despite the major economic and ecological importance of parasitoid insects, few studies have investigated the potential consequences of parasitoid mating failures on host-parasitoid population dynamics [6]
We demonstrate that (1) parasitoid populations can go extinct due to Allee effects, (2) extinctions are expected for parasitoids with cyclic dynamics or stable dynamics and aggregated attacks, and (3) with Allee effects, severe intraspecific competition in the host population increases parasitoid risk of extinction due to external factors decreasing population densities
Summary
Since the pioneering work of Nicholson and Bailey [1], many theoretical ecologists have been interested in modeling the tight interactions that occur between insect parasitoids and their hosts [2,3]. Demographic Allee effects are underpinned by component Allee effects, namely biological traits or trophic interactions that make individual fitness positively dependent on population size [17]. The most common and most often studied component Allee effect is the mate-finding Allee effect, which describes the difficulty that males and females experience in locating each other, and the consequent decline in reproduction at low population densities. Firm evidence of causal relations between mate-finding Allee effects and establishment success in insect populations is still relatively rare [11], mating failure at low density is often considered to be an important cause of demographic Allee effects in invading species [21,22,23,24,25]
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