Acanthaster coral predator density in the Pulau Dua area, Aceh Selatan

The crown of thorns starfish is one of the main threats to damage to coral reefs worldwide. Research on Acanthaster coral predator density in the Pulau Dua area, South Aceh district, has been carried out in March 2021, using the Line Intercept Transect (LIT) method. The results showed that the density Acanthaster planci obtained 42 individuals/12.000m2 with natural criteria. Corals fractures can support the life of Acanthaster planci substrate conditions dominated by coral fractures. It can also grow thread algae (Coraline) and encrusting algae, which will then be eaten by Acanthaster planci which are still in the larval stage. This research concludes that the density of Acanthaster planci obtained is still in the natural category with coral reef conditions including good criteria.

Complexity of a Discrete-Time Predator-Prey Model Involving Prey Refuge Proportional to Predator

In this paper, a discrete-time predator-prey model involving prey refuge proportional to predator density is studied. It is assumed that the rate at which prey moves to the refuge is proportional to the predator density. The fixed points, their local stability, and the existence of Neimark-Sacker bifurcation are investigated. At last, the numerical simulations consisting of bifurcation diagrams, phase portraits, and time-series are given to support analytical findings. The occurrence of chaotic solutions are also presented by showing the Lyapunov exponent while some parameters are varied.

Functional Response and Predation Potential of Carabus elysii Adults against the Terrestrial Slug Agriolimax agrestis

Terrestrial slugs are a prominent agricultural pest worldwide. To mitigate the negative effects of chemical pest control, biological control involves the use of natural enemies to reduce the impact of target pests. Numerous insects are natural predators of slugs. This study evaluated potential of the predatory species, Carabus elysii Thomson (Coleoptera: Carabidae) to biologically control the terrestrial slug, Agriolimax agrestis. Laboratory experiments were conducted to investigate the functional response, searching efficiency, and interference effect of female and male C. elysii adults regarding adult, immature, and juvenile A. agrestis individuals. The results show that both female and male ground beetle adults are functionally capable of preying on different sizes of terrestrial slugs. C. elysii exhibited Holling type II functional responses when preying on A. agrestis. The maximum daily prey consumption was 35.5 juveniles, 25.1 immatures, and 17.1 adults for adult females and 26.9 juveniles, 20.3 immatures, and 11.6 adults for adult males. The searching efficiency of female C. elysii adults regarding A. agrestis was always higher than that of male adults for identical ages and densities of A. agrestis. Moreover, the predation of C. elysii on slugs was affected by predator density. The disturbance coefficient of male C. elysii were the highest on adult A. agrestis. The results of this study suggest that female C. elysii exhibit a high potential for the biological control of A. agrestis.

Small-Scale Production of Amblyseius tamatavensis with Thyreophagus cracentiseta (Acari: Phytoseiidae, Acaridae)

Amblyseius tamatavensis, a predatory mite, has been mentioned as potentially useful for the control of Bemisia tabaci. The objective of this work was to compare the production rates of A. tamatavensis in closed units containing T. cracentiseta as food, at different combinations of numbers of predator inoculated, periods of production and volumes of rearing units. Final predator densities increased with increasing production periods up to 30–45 days, reducing afterward. Likewise, maximum final densities increased with increasing predator inoculation levels, up to 200 predators per rearing unit. The results led us to select the proportion of 150 predators per unit for a production period of 30 days to evaluate the effect of the size of the experimental unit. Then, in the second part of the study, a direct relationship was observed between volume and final predator density (y = 8610.25x + 2166.04; R2 = 0.99; p < 0.0001). It was also calculated that ri value was quite stable (0113–0.119), with a calculated value of 0.115 at all volumes of rearing units. It can be concluded that progressively larger numbers of predators can be obtained with progressively larger rearing units.

Temporally auto-correlated predator attacks structure ecological communities

For species regulated by a common predator, the P* rule predicts that the prey species that supports the highest mean predator density (P*) excludes the other prey species. This prediction is re-examined in the presence of temporal fluctuations in the vital rates of the interacting species including predator attack rates. When the fluctuations in predator attack rates are temporally uncorrelated, the P* rule still holds even when the other vital rates are temporally auto-correlated. However, when temporal auto-correlations in attack rates are positive but not too strongly, the prey species can coexist due to the emergence of a positive covariance between predator density and prey vulnerability. This coexistence mechanism is similar to the storage effect for species regulated by a common resource. Strongly positive or negative auto-correlations in attack rates generate a negative covariance between predator density and prey vulnerability and a stochastic priority effect can emerge: with non-zero probability either prey species is excluded. These results highlight how temporally auto-correlated species' interaction rates impact the structure and dynamics of ecological communities.

Increasing availability of palatable prey induces predator-dependence and increases predation on unpalatable prey

Understanding the factors governing predation remains a top priority in ecology. Using a dragonfly nymph-tadpole system, we experimentally varied predator density, prey density, and prey species ratio to investigate: (i) whether predator interference varies between prey types that differ in palatability, (ii) whether adding alternate prey influences the magnitude of predator interference, and (iii) whether patterns of prey selection vary according to the predictions of optimal diet theory. In single-prey foraging trials, predation of palatable leopard frog tadpoles was limited by prey availability and predator interference, whereas predation of unpalatable toad tadpoles was limited by handling time. Adding unpalatable prey did not affect the predator’s kill rate of palatable prey, but the presence of palatable prey increased the influence of predator density on the kill rate of unpalatable prey and reduced unpalatable prey handling time. Prey selection did not change with shifts in the relative abundance of prey types. Instead, predators selected easy-to-capture unpalatable prey at low total densities and harder-to-capture palatable prey at high densities. These results improve our understanding of generalist predation in communities with mobile prey, and illustrate that characteristics of the prey types involved govern the extent to which alternate prey influence the predator’s kill rate.

After 15 years, no evidence for trophic cascades in marine protected areas

In marine ecosystems, fishing often targets predators, which can drive direct and indirect effects on entire food webs. Marine reserves can induce trophic cascades by increasing predator density and body size, thereby increasing predation pressure on populations of herbivores, such as sea urchins. In California's northern Channel Islands, two species of sea urchins are abundant: the red urchin Mesocentrotus franciscanus , which is targeted by an economically valuable fishery, and the virtually unfished purple urchin Strongylocentrotus purpuratus . We hypothesized that urchin populations inside marine reserves would be depressed by higher predation, but that red urchins would be less affected due to fishing outside reserves. Instead, our analyses revealed that purple urchin populations were unaffected by reserves, and red urchin biomass significantly increased in response to protection. Therefore, urchin biomass overall has increased inside reserves, and we found no evidence that giant kelp is positively affected by reserves. Our results reveal the overwhelming direct effect of protecting fished species in marine reserves over indirect effects that are often predicted but seldom clearly documented. Indirect effects due to marine reserves may eventually occur in some cases, but very effective predators, large reserves or extended time periods may be needed to induce them.