Prey Density Research Articles

African Wild Dog Reproductive Capabilities Revisited: Successfully Raising Three Litters in Less than 14 Months is Possible

African wild dogs (Lycaon pictus) are obligate cooperative breeders and are generally considered mono-oestrus. As such, the birth of two litters within the same year rarely occurs, except for when pups from the initial litter are lost soon after birth. We report on a rare occurrence where a wild dog female (Vee) produced three litters of pups within a 13-month, 2-week period from March 2015 to June 2016, with surviving pups from each litter. Data on breeding females from wild dog packs in the study area (Savé Valley Conservancy, Zimbabwe) were used to identify whether any predictor variables (e.g. environmental or pack dynamics) could have influenced this unusual occurrence. The period over which the high number of litters were born had high prey densities and there was some evidence that it was associated with lower temperatures. High impala (Aepyceros melampus) densities during 2015 was likely to have been advantageous for the packs' hunting behaviours, while lower temperatures have been shown to increase the percentage of the day that is cool enough for wild dogs to hunt. Pack size during this period was higher in the pack that produced multiple litters (by the same female) than for other packs in the study site, which supports existing evidence that larger packs are able to produce more pups. Our results suggest that either 1) under ideal environmental and social conditions African wild dog females are capable of producing multiple litters throughout the year or that 2) this occurrence was an anomaly unique to Vee and her physiology.

Metacommunity stability and persistence for predation turnoff in selective patches

Predation as an important trophic interaction of ecological communities controls the large-scale patterns of species distribution, population abundance and community structure. Numerous studies address that predation can mediate diversity and regulate the ecological community and food web stability through changes in the behavior, morphology, development, and abundance of prey. Since predation has large effects on persistence and diversity, the local loss or removal of predation in a community can trigger a cascade of extinctions. In ecological theory, the effect of predation removal has been well studied in foodwebs, but it remains unclear in the case of a spatially distributed community connected by dispersal. In this study, the interaction between local and spatial processes is taken into account, we present how a predation turnoff in selective patches affects the synchronized oscillatory dynamics of a metacommunity. Using a simple predator–prey metacommunity with a diffusive dispersal, we show the impact of predation on synchronized, asynchronized and source–sink dynamics. Our results reveal that predation turnoff in very few patches stabilizes the metacommunity by damping the perfectly synchronized oscillatory state into multicluster equilibrium (i.e., steady) states. In a source–sink behavior, predation turnoff in a source patch reduces the number of sink patches and changes the clusters. In general, predation turnoff in low number of patches shows non-zero equilibrium states in both prey and predator populations, whereas predation turnoff in a larger number of patches can lead to the complete extinction of predators. Moreover, prey density from the patches where predation is absent goes to a saturating state near the carrying capacity. Thus, this study stresses that predation turnoff in selective patches acts as a stabilizing mechanism to promote the metacommunity persistence.

Intraspecific interactions at high predator densities affect the predation efficiency ofNeoseiulus californicus(Acari: Phytoseiidae) when prey density is low

AbstractQuantifying functional responses is a cornerstone in evaluating the predation efficiency of biological control agents such as predatory insects and mites. In this study, we investigate whether the efficiency ofNeoseiulus californicus(Acari: Phytoseiidae) in consuming prey is driven by intraspecific interactions. For this purpose, laboratory functional response experiments were conducted using one, two, three or four predators at several initial egg densities of the two‐spotted spider mite,Tetranychus urticae(Acari: Tetranychidae).The data fitted to the predator‐dependent Crowley–Martin model which accounts for intraspecific interactions. The results suggest that at high prey densities, i.e. the densities at which the predator is satiated, intraspecific interactions did not affect the predation potential ofN.californicus, as the maximum number ofT. urticaeeggs that can be attacked by predator individuals did not differ between treatments (i.e., predator densities).However, at low prey densities and the highest predator density (i.e., four individuals), intraspecific interactions were detected, as revealed by the estimated attack rates, i.e. the per capita prey consumption at low prey densities. While mean attack rates did not differ significantly when one, two and three predators were exposed to prey, when predator density increased to four individuals, attack rate was considerable lower compared to the other predator densities.These results indicate that intraspecific interactions are more intense at low prey densities, where the predator is not satiated and therefore digestion breaks do not exist. In contrast, at high prey densities digestion breaks exist, so that may fully accommodate the cost of intraspecific interactions. These results also suggest that predator density should be considered when functional responses are measured.

Dynamics Analysis of Predator-Prey Model with Double Allee Effects and Holling Type II Functional Response

In this article, a predator prey model with double Allee effects and Holling type II functional response is discussed. Strong and weak Allee effects were analyzed separately. The dynamic behavior of the model is analyzed by determining the equilibrium point and stability around the equilibrium point. From the analysis result, it is obtained that the trivial equilibrium point is locally asymptotically stable for the case of the strong Allee effect and the saddle unstable for the case of the weak Allee effect, while the boundary and coexistence equilibrium points are locally asymptotically stable if it satisfies several parameter conditions. Numerical simulations are carried out around the coexistence equilibrium point. The simulation results show that the Allee effect threshold affects prey population growth when experiencing a strong Allee effect. The growth of the prey population also depends on the initial conditions of the prey and predator population density. Furthermore, when the prey population experiences a weak Allee effect, there is no threshold must be exceeded for the population to survive so that for each initial condition however, the population will not experience extinction.

Survival of the sickest: selective predation differentially modulates ecological and evolutionary disease dynamics

Predators and parasites are critical, interconnected members of the community and have the potential to shape host populations. Predators, in particular, can have direct and indirect impacts on disease dynamics. By removing hosts and their parasites, predators alter both host and parasite populations and ultimately shape disease transmission. Selective predation of infected hosts has received considerable attention as it is recognized to have important ecological implications. The occurrence and consequences of preferential consumption of uninfected hosts, however, has rarely been considered. Here, we synthesize current evidence suggesting this strategy of selectively predating uninfected individuals is likely more common than previously anticipated and address how including this predation strategy can change our understanding of the ecology and evolution of disease dynamics. Selective predation strategies are expected to differentially impact ecological dynamics and therefore, consideration of both strategies is required to fully understand the impact of predation on prey and host densities. In addition, given that different strategies of prey selectivity by predators change the fitness payoffs both for hosts and their parasites, we predict amplified coevolutionary rates under selective predation of infected hosts compared to uninfected hosts. Using recent work highlighting the critical role that predators play in disease dynamics, we provide insights into the potential mechanisms by which selective predation on healthy individuals can directly affect ecological outcomes and impact long‐term host–parasite coevolution. We contrast the consequences of both scenarios of selective predation while identifying current gaps in the literature and future research directions.

Diet Composition and Prey Preference of Tiger, Leopard, and Dhole in Kalakkad-Mundanthurai Tiger Reserve, Southern Western Ghats, India

Comprehensive information on prey availability and diet composition is important to formulate effective conservation strategies. Data on these of large apex predators, the tiger Panthera tigris, leopard Panthera pardus, and dhole Cuon alpinus, are deficient in Kalakkad-Mundanthurai Tiger Reserve, India, which harbors low prey density. Therefore, we investigated how these predators coexisted by partitioning limited food resources. We found that prey selection and activity patterns differed among predators. The leopard (D [Jacobs' preference index] = +0.916) and dhole (D = +0.937) preferred the Indian chevrotain Moschiola indica, whereas the tiger preferred the gaur Bos gaurus (D = +0.937). Biomass of tiger's diet mainly consisted of the gaur (75%). In the dhole, the Indian chevrotain and sambar Rusa unicolor together contributed 91% of biomass, whereas 79% of leopard's biomass was contributed by the Nilgiri langur Semnopithecus johnii and the Indian chevrotain. The leopard and dhole had the highest dietary overlap (Ojk [Pianka Index] = 0.46). The highest activity overlap was found among the leopard, Indian chevrotain, and sambar. The leopard and dhole would compete for the Indian chevrotain, although the competition may be avoided by different activity patterns. Managements of the Indian chevrotain and gaur are critical for conserving large predators in the region.

Associations between abundances of free-roaming gamebirds and common buzzards Buteo buteo are not driven by consumption of gamebirds in the buzzard breeding season.

Releasing gamebirds in large numbers for sport shooting may directly or indirectly influence the abundance, distribution and population dynamics of native wildlife. The abundances of generalist predators have been positively associated with the abundance of gamebirds. These relationships have implications for prey populations, with the potential for indirect impacts of gamebird releases on wider biodiversity. To understand the basis of these associations, we investigated variation in territory size, prey provisioning to chicks, and breeding success of common buzzards Buteo buteo, and associations with variation in the abundances of free‐roaming gamebirds, primarily pheasants Phasianus colchicus, and of rabbits Oryctolagus cuniculus and field voles Microtus agrestis, as important prey for buzzards. The relative abundance of gamebirds, but not those of rabbits or voles, was weakly but positively correlated with our index of buzzard territory size. Gamebirds were rarely brought to the nest. Rabbits and voles, and not gamebirds, were provisioned to chicks in proportion to their relative abundance. The number of buzzard chicks increased with provisioning rates of rabbits, in terms of both provisioning frequency and biomass, but not with provisioning rates for gamebirds or voles. Associations between the abundances of buzzards and gamebirds may not be a consequence of the greater availability of gamebirds as prey during the buzzard breeding season. Instead, the association may arise either from habitat or predator management leading to higher densities of alternative prey (in this instance, rabbits), or from greater availability of gamebirds as prey or carrion during the autumn and winter shooting season. The interactions between gamebird releases and associated practices of predator control and shooting itself require better understanding to more effectively intervene in any one aspect of this complex social‐ecological system.

Does prey scarcity increase the risk of wolf attacks on domestic dogs?

Gray wolf Canis lupus predation on domestic dogs Canis familiaris is a considerable wolf–human conflict issue in several regions of Europe and North America but it has not been well documented in the scientific literature. Livestock depredations by wolves may be related to the abundance of wild prey. Regardless of the presumed motivations of wolves for attacking dogs (likely due to interference competition and predation), the abundance of wild prey populations may also influence the risk of wolf attacks on dogs. We examined whether the annual number of fatal attacks by wolves on dogs was related to the abundance of primary prey, including wild boar Sus scrofa and roe deer Capreolus capreolus in Estonia, as well as the abundance of moose Alces alces in Finland. Statistical models resulted in significant negative relationships, thus providing evidence that the risk of attacks in both house yards (Estonia) and hunting situations (Finland) was highest when the density of wild prey was low. Wild ungulates cause damage to agriculture and forestry, but they seem to mitigate conflicts between wolves and humans; therefore, it is necessary to develop a holistic, multispecies management approach in which the importance of wild ungulates for large carnivore conservation is addressed.

Fish and invertebrate use of restored vs. natural oyster reefs in a shallow temperate latitude estuary

AbstractCoastal marine habitats continue to be degraded, thereby compelling large‐scale restoration in many parts of the world. Whether restored habitats function similarly to natural habitats and fully recover lost ecosystem services is unclear. In estuaries, oyster reefs have been degraded by multiple anthropogenic activities including destructive fishing practices and reduced water quality, motivating restoration to maintain oyster fisheries and other ecosystem services, often at relatively high cost. We compared fish and invertebrate communities on recently restored (0–1 year post‐restoration), older restored (3–4 years post‐restoration), and natural oyster reefs to determine if and when restored reefs support functionally similar faunal communities. To test the influence of landscape setting on the faunal communities, the restored and natural reefs, as well as a control without reef present, were distributed among three landscapes (on the edge of salt marsh away from seagrass [salt marsh landscape], on mudflats [mudflat landscape], and near to seagrass and salt marsh [seagrass landscape]). Oyster density and biomass were greatest on restored reef habitat, as were those of non‐oyster bivalve species. Total abundance of invertebrates was much greater on oyster reefs than in control plots, regardless of reef or landscape type, yet were frequently highest on older restored reefs. Meanwhile, juvenile fish densities were greatest on natural reefs, at intermediate densities on older restored reefs, and least abundant on controls. When comparing the effects of reef age and landscape setting, juvenile fish densities were greatest on younger reefs within the mudflat landscape. Collectively, these results indicate that oyster reefs harbor higher densities of resident invertebrate prey, which may explain why reef habitat is also important for juvenile fish. Laboratory and field experiments supported the notion that gag grouper (a predatory demersal fish) forage more effectively on oyster reefs than on unstructured mud bottom, whereas our experiments suggest that flounders that utilize oyster reefs likely forage on adjacent mud bottom. Because landscape setting influenced fish and invertebrate communities on restored reefs, the ecological consequences of landscape setting should be incorporated into restoration decision making and site selection to enhance the recovery of ecosystem goods and services.

Impact of starvation on paternal reproductive investment in Neoseiulus californicus.

Neoseiulus californicus is an important biological control agent of small arthropod pests, widely used in preventive releases at low prey densities. Therefore, it is important to study reproductive investment of this species, both females and males, under environmental pressure of limited prey availability. Laboratory experiments were performed to investigate N. californicus male reproductive investment after short-time fasting or long-term starvation. When fasted for 36h, males are still able to complete a single mating with no significant change in reproductive parameters of its mate. But the total mating duration became 24% longer, especially timing for the male to fill the first spermatheca of its mate increased by 35%. If daily food availability was less than 20% of demand, males were still able to mate until the end of life, but their fertility reduced after ca. the seventh mating. Mating of some males at the end of their lives are invalid, with their mates failing to oviposit. Overall, we summarized that reproductive investment demand for a single mating was low in N. californicus males, but its priority in energy allocation was high. When starved, males tried to guarantee their mating capability, but their fertility decreased gradually.

A wolf in sheep's clothing: Predatory fish have convergent consumptive effects but divergent predation‐risk effects

AbstractAlthough consumptive effects of predators have long been central to ecology, predation‐risk effects have emerged as major components of predator–prey interactions. Both consumptive and predation‐risk effects should vary with predator functional traits (e.g., hunting mode, gape size), where consumption rates and induction of morphological and behavioral defenses correlate with prey‐specific predator threat. Ambush predators, in contrast with active predators, may face selection pressure to be cryptic to avoid detection by prey. Thus, ambush predators may change prey density through consumptive effects but have reduced or absent predation‐risk effects. We performed two mesocosm experiments with free‐roaming and caged predators to explore post‐colonization interactions of the chemically camouflaged, large‐gaped, ambush predator, pirate perch (Aphredoderus sayanus), active, large‐gaped green sunfish (Lepomis cyanellus), and active, small‐gaped golden topminnow (Fundulus chrysotus), with larval gray treefrogs (Hyla chrysoscelis) and mole salamanders (Ambystoma talpoideum). We examined the consumptive and predation‐risk effects of each predator on amphibian mortality, growth rates, tail morphology, and polyphenisms. Large‐gaped pirate perch and green sunfish had strong, equivalent consumptive effects, but only the free‐roaming active predator, green sunfish, suppressed the growth of survivors through risk‐induced trait responses. Caged green sunfish induced much stronger non‐consumptive mortality than pirate perch in gray treefrogs, an effect that was absent for mole salamanders; golden topminnows had intermediate effects. Tail defenses were a function of prey mortality and only manifested in free‐roaming predator treatments, suggesting the necessity of predator attacks or conspecific alarm signals. Likewise, mole salamander polyphenism was unaffected by caged predators, whereas free‐roaming green sunfish prevented all metamorphosis. Free‐roaming golden topminnows increased the proportion of individuals remaining as larvae, and pirate perch increased the proportion of paedomorphs and metamorphs. Overall, the prey had positively correlated anti‐predator responses across life stages, suggesting multicomponent defenses. Predator effects varied with functional traits with large‐gaped predators having strong consumptive effects, but active predators causing stronger risk‐induced changes in growth compared to cryptic ambush predators, which provides more evidence for chemical camouflage. Our results emphasize the role of hunting mode and gape size in determining consumptive and predation‐risk effects, and that predation‐risk effects cannot be reliably predicted from consumptive effects.

A Mathematical Modelling Approach for a Past-Dependent Prey-Predator System

A memory dependent prey-predator model incorporating Allee effect in prey is analysed. For a small and high values of memory rate, the dynamical changes in the prey and predator densities are demonstrated. The equilibria of the proposed model and the local stability analysis corresponding to each equilibrium are presented. The variables of prey and predator species with respect to memory rate are investigated and the existence of the Hopf bifurcation is shown. The analytical part of this paper is supported with detailed numerical simulations.

A parabolic-quasilinear predator-prey model under pursuit-evasion dynamics

For positive parameters α and β restricted to a certain condition, we prove the global solvability of the parabolic-quasilinear system{∂tu−Δu+∇⋅(u∇p)=αuw−u∂tw−∇⋅(Ψ(w)∇w)−∇⋅(w∇q)=βw(1−w−u) where p and q are the solutions of ∂tp−αpΔp=δ‾ww−δ‾pp and ∂tq−αqΔq=δ‾uu−δ‾qq, respectively, Ψ∈C2([0,+∞)) positive, and complemented with appropriated initial data and Neumann boundary condition. This system models a predator-prey interaction with pursuit and evasion, where u represents the predator density, w represents the prey density, p and q are the pheromone of the species. The result of this article extends the result of [3] without considering any assumption under the asymptotic behaviour of pheromone production of the predator as in there. The results presented here contribute to the results presented in [2,3], in particular, it is the first result collaborating with [14] in the relevant case b≡0 in there.

Quantifying predator functional responses under field conditions reveals interactive effects of temperature and interference with sex and stage.

Predator functional responses describe predator feeding rates and are central to predator–prey theory. Originally defined as the relationship between predator feeding rates and prey densities, it is now well known that functional responses are shaped by a multitude of factors. However, much of our knowledge about how these factors influence functional responses is based on laboratory studies that are generally logistically constrained to examining only a few factors simultaneously and that have unclear links to the conditions organisms experience in the field.We apply an observational approach for measuring functional responses to understand how sex/stage differences, temperature and predator densities interact to influence the functional response of zebra jumping spiders on midges under natural conditions.We used field surveys of jumping spiders to infer their feeding rates and examine the relationships between feeding rates, sex/stage, midge density, predator density and temperature using generalized additive models. We then used the relationships supported by the models to fit parametric functional responses to the data.We find that feeding rates of zebra jumping spiders follow some expectations from previous laboratory studies such as increasing feeding rates with body size and decreasing feeding rates with predator densities. However, in contrast to previous results, our results also show a lack of temperature response in spider feeding rates and differential decreases in the feeding rates of females and juveniles with densities of different spider sexes/stages.Our results illustrate the multidimensional nature of functional responses in natural settings and reveal how factors influencing functional responses can interact with one another through behaviour and morphology. Further studies investigating the influence of multiple mechanisms on predator functional responses under field conditions will increase our understanding of the drivers of predator–prey interaction strengths and their consequences for communities and ecosystems.

Uncertainty in foraging success and its consequences on fitness

Optimal foraging models are commonly used to determine the strategy maximizing the proxies for fitness, such as foraging success. The strategies maximizing the proxy for fitness and fitness are assumed to be the same. However, this study shows that this assumption can be invalid when the relationship between the proxy for fitness and fitness is nonlinear and the foraging success is uncertain. A well-known prey choice model that uses long-term energy intake rate as the proxy for fitness was used as an example. This model considers a situation where predators predate on two types of prey that differ in quality, that is, one (primary prey) has higher quality than the other (alternative prey). A strategy can be represented by the probability of attacking alternative prey upon encounter while always attacking primary prey. The probability of attacking alternative prey that maximizes the expected rate of energy intake is either 0 or 1 depending on the density of primary prey (known as the zero–one rule). Meanwhile, the density of alternative prey has no influence on the optimal strategy. A simulation model was used to characterize the stochastic outcomes in the rate of energy intake in a finite foraging duration. The results revealed that foraging strategy influences the expected rate of energy intake and the uncertainty around the expectation. Consequently, the strategies maximizing the rate of energy intake and fitness may not be the same when the relationship between the rate of energy intake and fitness is nonlinear due to Jensen’s inequality. Previous results such as the zero–one rule and the independence of the optimal strategy on the availability of alternative prey are no longer valid when fitness, rather than the proxy for fitness, is explicitly considered in a finite foraging duration.

Effects of prey density and flow speed on plankton feeding by garden eels: a flume study.

ABSTRACTFeeding by zooplanktivorous fish depends on their foraging movements and the flux of prey to which they are exposed. While prey flux is a linear function of zooplankton density and flow speed, those two factors are expected to contribute differently to fish movements. Our objective was to determine the effects of these factors for garden eels, stationary fish that feed while anchored to the sandy bottom by keeping the posterior parts of their bodies inside a burrow. Using a custom-made flume with a sandy bottom, we quantified the effects of prey density and flow speed on feeding rates by spotted garden eels (Heteroconger hassi). Feeding rates increased linearly with prey density. However, feeding rates did not show a linear relationship with flow speed and decreased at 0.25 m s−1. Using label-free tracking of body points and 3D movement analysis, we found that the reduction in feeding rates was related to modulation of the eel's movements, whereby the expected increase in energy expenditure was avoided by reducing exposure and drag. No effects of flow speed on strike speed, reactive distance or vectorial dynamic body acceleration (VeDBA) were found. A foraging model based on the body length extended from the burrow showed correspondence with observations. These findings suggest that as a result of their unique foraging mode, garden eels can occupy self-made burrows in exposed shelter-free sandy bottoms where they can effectively feed on drifting zooplankton.

Population responses of omnivorous arthropods to plant alternative resources suppress prey populations: A meta-analysis.

Omnivory is ubiquitous in ecological communities. Yet, we lack a consensus of how plant alternative resources impact the ability of omnivores to suppress prey populations. Previous work suggests that plant alternative resources can increase, decrease, or have no effect on the magnitude of omnivore-prey interactions. This discrepancy may arise from (1) the ability of omnivore populations to respond to plant alternative resources and (2) identity-specific effects of plant alternative resources. We used a meta-analysis to examine how omnivore population responses and the identity of plant alternative resources affect (1) omnivore predation rates (mainly reported as per capita predation rate) and (2) omnivore impacts on prey population density. Plant alternative resources reduced omnivore predation rate regardless of identity. The suppression of the predation rate by flowers and flowering plants was magnified when pollen alone was tested as the alternative resource. Surprisingly, plant alternative resource availability reduced prey density, suggesting that omnivore predation increased with plant alternative resources. This discrepancy (plant alternative resources not only decreased omnivore predation rates but also decreased prey density) resulted from experimental differences in the ability of omnivore populations to respond to plant alternative resources. In the presence of plant alternative resources, allowing omnivore population responses decreased prey density, while not allowing population responses increased prey density. Because omnivores commonly suppress prey density in the presence of plant alternative resources when population responses of omnivores are allowed, the effectiveness of biological control may depend upon the availability of such resources and the facilitation of population responses.

Quantifying the relationship between prey density, livestock and illegal killing of leopards

AbstractMany large mammalian carnivores are facing population declines due to illegal killing (e.g. shooting) and habitat modification (e.g. livestock farming). Illegal killing occurs cryptically and hence is difficult to detect. However, reducing illegal killing requires a solid understanding of its magnitude and underlying drivers, while accounting for the imperfect detection of illegal killing events. Despite the importance of illegal killing of large carnivores in comparison with other causes of mortality, its relationship with potential drivers such as livestock density and wild prey abundance is rarely described.Using ranger‐collected data (2007–2019) of leopard killing events and data on covariates (livestock density, wild prey abundance, road length, protected area size, elevation) across Iran, we applied a single‐visit N‐mixture model to jointly model variation in detection probability and expected annualized number of leopard killing events.Over the study period, we estimated 428 leopard mortalities (95% CI 184 to 1,014), which was 45% larger than the observed number. Expected intensity of leopard killing was positively related to protected area size, livestock density and wild prey abundance. Detection of leopard killing was higher in areas with more developed road networks.Synthesis and applications. Ranger‐based monitoring data on poaching of carnivores are cost effective, but traditional analysis does not take into account imperfect detection. We show that innovative statistics (single‐visit N‐mixture modelling) can reliably quantify poaching events and address their drivers, at large geographical scales. We used the example of the Persian leopard across Iran, but our approach is also applicable to understand killing dynamics of other species. Results suggest that a high frequency of leopard killing is likely to occur in areas with >100 livestock per km2and >450 individuals of wild prey per km2. This highlights the need for improved management of livestock grazing and effective measures around high‐risk protected areas to mitigate human–leopard conflict and reduce killing of leopards.

Impacts of an invasive alga on recruitment of a temperate reef fish

The invasive brown macroalga, Sargassum horneri (devil weed), has spread along the southern California coast, replacing the native habitat-forming macroalga, Macrocystis pyifera (giant kelp). M. pyrifera is a critical habitat for macroalgal-associated fishes, especially for the arrival and survival of juvenile fish that constitutes recruitment success. It is unclear whether critical processes in recruitment may be altered if S. horneri replaces M. pyrifera as the dominant biogenic macroalgal habitat on rocky reefs. Through a series of laboratory experiments, we investigated the effects of macroalgal identity on post-settlement processes contributing to recruitment success for a common macrophyte-associated fish, Heterostichus rostratus (giant kelpfish). To evaluate the potential impacts of S. horneri vs. M. pyrifera in their effects on juvenile H. rostratus, we explored whether there were differences for H. rostratus in their (1) habitat choice in the presence of both macroalgae, (2) prey choice employing the mysid shrimp, Holmesimysis costata, that were fed on either of the two macroalgae, and (3) predator-mediated mortality by Paralabrax clathratus (kelp bass), a common piscivore in both macroalgal habitats. The results of these experiments suggest that for the post-settlement processes evaluated here, macroalgal identity does not appear to have a significant impact on giant kelpfish, and recruitment success in S. horneri habitat may be equivalent to that observed in M. pyrifera. It is possible, however, that differential settlement to these macroalgae, species-specific habitat requirements, or other post-settlement factors may play a role in influencing recruitment success within each of these two habitats. Conducting further studies that include ambient invertebrate prey densities of H. rostratus in each macroalgal habitat, particularly in a field setting, will potentially provide greater insight into these processes.

Biology and functional response of the predator, Dortus primarius (Distant) (Hemiptera: Miridae) preying on Frankliniella schultzei (Trybom) (Thysanoptera: Thripidae)

BackgroundDortus primarius (Distant) (Hemiptera: Miridae) is a general predator reported from the oriental region. This bug is naturally found in many crop ecosystems where it feeds on thrips, aphids, insect eggs and other soft-bodied insects. Although, the rearing protocol of this predatory mirid has been developed, the efficiency of this predator as a biocontrol agent is limited and needs to be investigated. The thrips, Frankliniella schultzei (Trybom) (Thysanoptera: Thripidae), is a polyphagous pest that attacks many crops in polyhouse in India. Therefore, in the present study, biology and functional response of this predator to different densities of F. schultzei larvae in the laboratory was investigated.ResultsThe mirid predator was able to develop from egg to adulthood on tomato infested plant with F. schultzei larvae in 23–24 days with 15 and 11.76% mortality of 4th and 5th instar nymphs, respectively. Both 5th instar and female adults exhibited a type III functional response. At highest prey density (40) both 5th instar and female adults consumed 21.6 and 28.6 thrips larvae per day, respectively. Functional response parameters, viz. attack rate, handling time, a/Th and T/Th showed the potency of this predator against F. schultzei.ConclusionBased on the high fecundity, predation rate and density dependent behaviour, it is predicted that D. primarius might be an efficient and potential predator. However, further research is needed to assess its release rate and other ecological studies in the field situation.