Neimark–Sacker Bifurcation and Stability of a Certain Class of Host-Parasitoid Models with Host Refuge Effect

In this paper, we consider the dynamics of a certain class of host-parasitoid models, where some hosts are completely free from parasitism either with or without a spatial refuge and the host population is governed by the Beverton–Holt equation. We assume that, in each generation, a constant portion of the host population may find a refuge and be safe from the attack by parasitoids. We derive some criteria for the Neimark–Sacker bifurcation. Then, we apply the developed theory to the three well-known cases: [Formula: see text] model, Hassel and Varley model, and parasitoid–parasitoid model. Intensive numerical calculations suggest that the last two models undergo a supercritical Neimark–Sacker bifurcation.

The spatial heterogeneity of the gut limits bacteriophage predation leading to the coexistence of antagonist populations of bacteria and their viruses

Bacteria and their viruses, bacteriophages (phages), are the most abundant components of the mammalian gut microbiota where these two entities coexist over time. The ecological dynamics underlying the coexistence between these two antagonistic populations in the gut are unknown. We challenged a murine synthetic bacterial community with a set of virulent phages, to study the factors allowing phages-bacteria coexistence in the gut. We found that coexistence was neither dependent on an arms race between bacteria and phages, nor on the ability of phages to extend host range. Instead, our data suggest that some phage-inaccessible sites in the mucosa of the ileum serve as a spatial refuge for bacteria, which from there disseminate in the gut lumen. Luminal phages amplify by infecting luminal bacteria maintaining phage throughout the gut. We conclude that the heterogeneous distribution of microbes in the gut contributes to the long-term coexistence of phages with phage-susceptible bacteria. This observation could explain the persistence in the human gut of intestinal phages, such as the crAssphage, as well as the low efficiency of oral phage therapy against enteric pathogens in animal models and clinical trials.

Dispersal in Host–Parasitoid Interactions: Crop Colonization by Pests and Specialist Enemies

Interactions of insect pests and their natural enemies increasingly are being considered from a metapopulation perspective, with focus on movements of individuals among habitat patches (e.g., individual crop fields). Biological control may be undercut in short-lived crops as natural enemies lag behind the pests in colonizing newly created habitat. This hypothesis was tested by assessing parasitism of cereal leaf beetle (Oulema melanopus) and alfalfa weevil (Hypera postica) larvae at varying distances along transects into newly planted fields of small grains and alfalfa in northern Utah. The rate of parasitism of cereal leaf beetles and alfalfa weevils by their host-specific parasitoids (Tetrastichus julis (Eulophidae) and Bathyplectes curculionis (Ichneumonidae), respectively) was determined for earliest maturing first generation host larvae. Rates of parasitism did not vary significantly with increasing distance into a newly planted field (up to 250–700 m in individual experiments) from the nearest source field from which pest and parasitoid adults may have immigrated. These results indicate strong, rapid dispersal of the parasitoids in pursuing their prey into new habitat. Thus, across the fragmented agricultural landscape of northern Utah, neither the cereal leaf beetle nor the alfalfa weevil initially gained substantial spatial refuge from parasitism by more strongly dispersing than their natural enemies into newly created habitat. Additional studies, including those of colonization of newly planted crops by generalist pests and natural enemies, are called for in assessing these results with a broader perspective.

Periwinkle climbing response to water- and airbone predator chemical cues may depend on home-marsh geography

The salt marsh periwinkle, Littorina irrorata, exhibits a spatial refuge from predation by climbing the stems of Spartina alterniflora in order to avoid benthic predators. Salt marsh periwinkles have a broad geographic distribution, and for many species, responses to predators also varies with biogeography. This study sought to determine if the geographical location of the home marsh influenced the response of periwinkles (climbing height) to blue crab predator cues both via air and water. Snails from Louisiana (LA) climbed higher in general than those from North Carolina (NC), regardless of chemical cue. However, LA snails climbed 11 cm higher in the presence of waterborne predators than control snails with no cue, while NC snails only climbed five cm higher in the same comparisons. Airborne chemical cue tended to have snails climbing at intermediate heights. These responses were significantly enhanced when both populations of snails were housed together. Periwinkle response to predator cues was stronger in LA than NC, and so it is possible that the behavioral response of these snails to predators varies with biogeography of the home marsh. Also interestingly, the results of this study also suggest that cue delivery is probably occurring via mechanisms other than water, and potentially via airborne cues. Therefore, salt marsh periwinkles likely respond to numerous cues that initiate behavioral responses, including airborne cues, and these responses may vary by home-marsh geography.

Periwinkle climbing response to water- and airbone predator chemical cues may depend on home-marsh geography

The salt marsh periwinkle, Littorina irrorata, exhibits a spatial refuge from predation by climbing the stems of Spartina alterniflora in order to avoid benthic predators. Salt marsh periwinkles have a broad geographic distribution, and for many species, responses to predators also varies with biogeography. This study sought to determine if the geographical location of the home marsh influenced the response of periwinkles (climbing height) to blue crab predator cues both via air and water. Snails from Louisiana (LA) climbed higher in general than those from North Carolina (NC), regardless of chemical cue. However, LA snails climbed 11cm higher in the presence of waterborne predators than control snails with no cue, while NC snails only climbed 5cm higher in the same comparisons. Airborne chemical cue tended to have snails climbing at intermediate heights. These responses were significantly enhanced when both populations of snails were housed together. Periwinkle response to predator cues was stronger in LA than NC, and so it is possible that the behavioral response of these snails to predators varies with biogeography of the home marsh. Also interestingly, the results of this study also suggest that cue delivery is probably occurring via mechanisms other than water, and potentially via airborne cues. Therefore, salt marsh periwinkles likely respond to numerous cues that initiate behavioral responses, including airborne cues, and these responses may vary by home-marsh geography.

Periwinkle climbing response to water- and airbone predator chemical cues may depend on home-marsh geography

The salt marsh periwinkle, Littorina irrorata, exhibits a spatial refuge from predation by climbing the stems of Spartina alterniflora in order to avoid benthic predators. Salt marsh periwinkles have a broad geographic distribution, and for many species, responses to predators also varies with biogeography. This study sought to determine if the geographical location of the home marsh influenced the response of periwinkles (climbing height) to blue crab predator cues both via air and water. Snails from Louisiana (LA) climbed higher in general than those from North Carolina (NC), regardless of chemical cue. However, LA snails climbed 11cm higher in the presence of waterborne predators than control snails with no cue, while NC snails only climbed 5cm higher in the same comparisons. Airborne chemical cue tended to have snails climbing at intermediate heights. These responses were significantly enhanced when both populations of snails were housed together. Periwinkle response to predator cues was stronger in LA than NC, and so it is possible that the behavioral response of these snails to predators varies with biogeography of the home marsh. Also interestingly, the results of this study also suggest that cue delivery is probably occurring via mechanisms other than water, and potentially via airborne cues. Therefore, salt marsh periwinkles likely respond to numerous cues that initiate behavioral responses, including airborne cues, and these responses may vary by home-marsh geography.