Nonlinearities Lead to Qualitative Differences in Population Dynamics of Predator-Prey Systems

Abstract

Since typically there are many predators feeding on most herbivores in natural communities, understanding multiple predator effects is critical for both community and applied ecology. Experiments of multiple predator effects on prey populations are extremely demanding, as the number of treatments and the amount of labour associated with these experiments increases exponentially with the number of species in question. Therefore, researchers tend to vary only presence/absence of the species and use only one (supposedly realistic) combination of their numbers in experiments. However, nonlinearities in density dependence, functional responses, interactions between natural enemies etc. are typical for such systems, and nonlinear models of population dynamics generally predict qualitatively different results, if initial absolute densities of the species studied differ, even if their relative densities are maintained. Therefore, testing combinations of natural enemies without varying their densities may not be sufficient. Here we test this prediction experimentally. We show that the population dynamics of a system consisting of 2 natural enemies (aphid predator Adalia bipunctata (L.), and aphid parasitoid, Aphidius colemani Viereck) and their shared prey (peach aphid, Myzus persicae Sulzer) are strongly affected by the absolute initial densities of the species in question. Even if their relative densities are kept constant, the natural enemy species or combination thereof that most effectively suppresses the prey may depend on the absolute initial densities used in the experiment. Future empirical studies of multiple predator – one prey interactions should therefore use a two-dimensional array of initial densities of the studied species. Varying only combinations of natural enemies without varying their densities is not sufficient and can lead to misleading results.

Classical Biological Control of Invasive Legacy Crop Pests: New Technologies Offer Opportunities to Revisit Old Pest Problems in Perennial Tree Crops

“…These models have demonstrated that natural enemy activity sometimes causes significant declines in pest densities [ 63 ]. However, as the number of variables increases, especially with respect to natural enemy species interacting with the pest, resulting population dynamics are complicated owing to non-linear effects (e.g., natural enemy behaviors) and model outcomes may be sensitive to initial starting population densities [ 64 ].…”

Evaluating the Structure of Enemy Biodiversity Effects on Prey Informs Pest Management

“…These results suggest that increasing enemy biodiversity and whitefly control in tomatoes can be compatible and related goals [66]. At the same time, it must be acknowledged that interaction strength between natural enemies may greatly vary in different contexts (e.g., [24]). In fact, the net result of the interaction between natural enemies and prey in agroecosystems has always some level of uncertainty and context dependence.…”

“…With respect to the role of natural enemy biodiversity on pest control, biodiversity and ecosystem function studies typically explore the extent to which prey suppression is affected by variation of enemy biodiversity [4][5][6][7][8][9][10]. In fact, different aspects of enemy biodiversity including species identity [11][12][13][14], complementary prey use [6,[15][16][17], behavioural and ecological interactions between predators [18][19][20][21][22], and abundance [10,23,24] can determine emergent effects of enemy biodiversity on prey. Moreover, it is also becoming increasingly evident that emergent properties of enemy communities are context dependent and often arise from several simultaneous mechanisms that individually might produce linear or nonlinear, negative, null, and positive effects on prey suppression [5,8,9,[24][25][26].…”

“…In fact, different aspects of enemy biodiversity including species identity [11][12][13][14], complementary prey use [6,[15][16][17], behavioural and ecological interactions between predators [18][19][20][21][22], and abundance [10,23,24] can determine emergent effects of enemy biodiversity on prey. Moreover, it is also becoming increasingly evident that emergent properties of enemy communities are context dependent and often arise from several simultaneous mechanisms that individually might produce linear or nonlinear, negative, null, and positive effects on prey suppression [5,8,9,[24][25][26]. It is therefore important to investigate multiple mechanisms underlying the link between enemy biodiversity and prey suppression to parse out the main processes determining pest control service provision in diverse agroecosystems [17,26,27].…”

Intraguild interactions between two biological control agents in citrus fruit: implications for biological control of medfly

“…One S. cameroni mated female was initially used per density. Nevertheless, to prevent the results from being affected by the initial densities of the involved species – probably due to non‐linearities in the system (Ameixa et al, ) – we repeated the experiment with three times larger initial numbers of hosts and parasitoids, thus, keeping constant their relative densities, although varying their absolute densities. Translucent plastic boxes (20 cm × 15 cm × 10 cm), closed with a tight‐fitting lid that had a 4‐cm diameter gauze‐covered hole for ventilation, were used as experimental units.…”