Habitat selection of two gobies (Microgobius gulosus, Gobiosoma robustum): influence of structural complexity, competitive interactions, and presence of a predator

Herein I compare the relative importance of preference for structurally complex habitat against avoidance of competitors and predators in two benthic fishes common in the Gulf of Mexico. The code goby Gobiosoma robustum Ginsburg and clown goby Microgobius gulosus (Girard) are common, ecologically similar fishes found throughout the Gulf of Mexico and in the southeastern Atlantic Ocean. In Florida Bay, these fishes exhibit habitat partitioning: G. robustum is most abundant in seagrass-dominated areas while M. gulosus is most abundant in sparsely vegetated habitats. In a small-scale field survey, I documented the microhabitat use of these species where their distributions overlap. In a series of laboratory experiments, I presented each species with structured (artificial seagrass) versus nonstructured (bare sand) habitats and measured their frequency of choosing either habitat type. I then examined the use of structured versus nonstructured habitats when the two species were placed together in a mixed group. Finally, I placed a predator (Opsanus beta) in the experimental aquaria to determine how its presence influenced habitat selection. In the field, G. robustum was more abundant in seagrass and M. gulosus was more abundant in bare mud. In the laboratory, both species selected grass over sand in allopatry. However, in sympatry, M. gulosus occupied sand more often when paired with G. robustum than when alone. G. robustum appears to directly influence the habitat choice of M. gulosus: It seems that M. gulosus is pushed out of the structured habitat that is the preferred habitat of G. robustum. Thus, competition appears to modify the habitat selection of these species when they occur in sympatry. Additionally, the presence of the toadfish was a sufficient stimulus to provoke both M. gulosus and G. robustum to increase their selection for sand (compared to single-species treatments). Distribution patterns of M. gulosus and G. robustum likely result from a synthesis of various biotic and abiotic filters, including physiological tolerances to environmental factors, dispersal ability of larvae, and availability of food. Selection for structural complexity, competition, and presence of predators may further define the resulting pattern of distribution observed in the field.     

Variability in response of four populations of Amblyseius largoensis (Acari: Phytoseiidae) to Raoiella indica (Acari: Tenuipalpidae) and Tetranychus gloveri (Acari: Tetranychidae) eggs and larvae

Raoiella indica (Acari: Tenuipalpidae) is a phytophagous mite that recently invaded the Neotropical region. A predatory mite Amblyseius largoensis (Acari: Phytoseiidae) has been found associated with R. indica in Florida. This study evaluated A. largoensis by determining its likelihood of consuming eggs and larvae of R. indica and Tetranychus gloveri (Acari: Tetranychidae) under no-choice and choice conditions. To detect variations in the response of A. largoensis to R. indica, four populations of predators were examined: (1) predators reared exclusively on R. indica in the laboratory for 2 years, (2) predators reared on T. gloveri in the laboratory for 2 months but reared on R. indica for 2 years previously, (3) predators collected from a field infested with R. indica, and (4) predators collected from a field that had never been infested with R. indica. Results of this study suggest that A. largoensis is likely to accept and consume high numbers of R. indica eggs regardless of their previous feeding experience. In contrast, all populations consumed relatively fewer R. indica larvae than the other prey tested. Predators previously exposed to R. indica were more likely to consume R. indica larvae. By contrast, predators not previously exposed to R. indica showed the lowest likelihood of choosing to feed on this prey item. Plasticity in the response of A. largoensis to R. indica larvae could be associated to selection, learning, or a combination of both. The possible implications of the observed differences in terms of biological control of R. indica are discussed.     

Development,metamorphosis, and natural history of the nudibranch Doridella obscura Verrill (Corambidae: Opisthobranchia)

The doridacean nudibranch Doridella obscura Verrill was raised through one complete generation in laboratory culture, and spawning behavior monitored for a year at monthly intervals in Barnegat Bay, New Jersey.The nudibranch deposited egg masses throughout the year in Barnegat Bay, and the larvae remained viable at temperatures ranging from 1.5 to 28 °C. At 25 °C the eggs hatch 4 days after oviposition, and the planktotrophic veliger larvae swim and feed for 9 days before they metamorphose. Settlement occurs specifically on the bryozoan Electro crustulenta (Pallas). The spirally coiled larval shell grows rapidly until the dorsal mantle fold is retracted from the aperture 5–6 days after hatching. Although starved larvae grow only slightly and do not metamorphose, they resume normal development on introduction of suitable food. Newly metamorphosed juveniles consume algae and debris on the surface of the bryozoan until they grow large enough to attack the living zooids of E. crustulenta.The life cycle of Doridella obscura is short (26 days at 25 °C), allowing the nudibranchs to take advantage of short-lived Electra crustulenta colonies in unstable habitats in bays and estuaries.     

Effect of light and substratum complexity on microhabitat selection and activity of the ophiuroid Ophiopholis aculeata

We evaluated the effect of light intensity and substratum complexity on habitat preference and displacement speed of the ophiuroid Ophiopholis aculeata. The ophiuroid strongly preferred reduced light and to a lesser extent complex substrata. Further, displacement speed increased with light intensity and decreased with substratum complexity (ophiuroids were virtually immobile on darkened complex substrata). In the field, the density of exposed ophiuroids, with the disk out of a crevice, was always low, irrespective of the intensity of solar radiation. However, the extent to which they extended their arms (to feed) was inversely related to light intensity, as the number of suspension-feeding arms was low under direct sunlight, intermediate under indirect light and high at night. Field observations showed that the response to light was not modified when UV radiation was eliminated with a filter, and a laboratory experiment showed that white light intensity alone produced patterns similar to those observed in the field. O. aculeata may reduce arm extension with increasing light intensity to reduce the threat of visual predators, whose foraging efficiency increases with light intensity. However, visual predators are rare in our study site. We hypothesize that the large-scale larval dispersion of O. aculeata (due to the long pelagic phase) prevents ophiuroids from adapting to local conditions so that its response to light reflects adaptation to visual predators in other locations.     

The relationship of hunger to predatory behaviour in hawks (Falco sparverius and Buteo platypterus)

The relationship of hunger (as measured by food consumption) to predatory behaviour in two species of falconiform birds was investigated in the laboratory. The tendency to kill prey was correlated with hunger, and only hungry birds killed prey. I suggest that there is no predatory instinct or drive which operates independently of hunger and offer other rationales for the occasional excessive killing by some vertebrate predators. Falco sparverius exhibited a circadian rhythm of hunger and killing by some vertebrate predators. Falco sparverius exhibited a circadian rhythm of hunger and killing tendency, with a peak in the late afternoon. Buteo platypterus possibly showed a slight peak in the morning.     

Predator-prey interaction between hatchery-reared Japanese flounder juvenile, Paralichthysolivaceus, and sandy shore crab, Matutalunaris: daily rhythms, anti-predator conditioning and starvation

Predator-prey interaction between sandy shore crab, Matuta lunaris (Forskål, 1775), and juvenile Japanese flounder, Paralichthys olivaceus (Temminck et Schlegel), was investigated under controlled laboratory conditions. Possibility of training and conditioning hatchery-reared flounder to avoid predators was also examined. Crabs took over 75% of their daily ration at night when they were given access to prey 24 h a day. Large (64.8±5.4 g)- and medium (30.68±3.33 g)-sized crabs ate ca. 5.5±1.45 and 3.9±1.99 individuals of flounder (TL=4.96±0.23 cm) a day, respectively. When flounder juveniles that have experienced predation pressure by crabs encountered predators again, they exhibited better survival compared to the naive fish. Flounder juveniles were also conditioned either using small and, thus, benign predators, or large crabs over fence. The conditioned fish with either method were better able to avoid capture by crabs than naive fish, revealing that learning process should play an important role in their predator avoidance. Anti-predator performance was also compared between starved and fed flounder juveniles. Fed fish were rarely eaten by predators after 3 h of exposure, whereas starved fish continued to be eaten. Our results suggest that stock-enhancement program of Japanese flounder can be improved by applying proper feeding protocol and conditioning to avoid predators prior to release. Present research supports the idea that behavioural and ecological consideration for the target species is indispensable for the success of stock enhancement.     

Predation by juvenile Polinices duplicatvs (Say) on Gemma gemma (Totten)

Feeding by juvenile Polinices duplicatus (Say) on Gemma gemma (Totten) at Barnstable Harbor, Massachusetts, was examined using laboratory experiments and collections of naturally occurring bored shells. Snails < 19 mm fed on Gemma in the laboratory and borehole diameter was directly related to predator size. Field collections of drilled shells showed that Gemma was an important prey of 0-year-class Polinices. Boreholes in Gemma shells from field collections were made primarily by snails of 1– mm, and < 3% were made by snails of > 10 mm. Most bored Gemma were large 1- to 2-yr-old individuals. The proportion of empty Gemma shells containing boreholes ranged from 3.7–14.6%, indicating that naticid prédation was a minor source of total Gemma mortality. Collections of bored shells closely reflected both the size range and relative abundance of natural predators of Gemma.     

Prey selection and the functional response of sea stars (Asterias vulgaris Verrill) and rock crabs (Cancer irroratus Say) preying on juvenile sea scallops (Placopecten magellanicus (Gmelin)) and blue mussels (Mytilus edulis Linnaeus)

Predators in nature include an array of prey types in their diet, and often select certain types over others. We examined (i) prey selection by sea stars (Asterias vulgaris) and rock crabs (Cancer irroratus) when offered two prey types, juvenile sea scallops (Placopecten magellanicus) and blue mussels (Mytilus edulis), and (ii) the effect of prey density on predation, prey selection, and component behaviours. We quantified predation rates, behavioural components (proportion of time spent searching for prey, encounter probabilities) and various prey characteristics (shell strength, energy content per prey, handling time per prey) to identify mechanisms underlying predation patterns and to assess the contribution of active and passive prey selection to observed selection of prey. Sea stars strongly selected mussels over scallops, resulting from both active and passive selection. Active selection was associated with the probability of attack upon encounter; it was higher on mussels than on scallops. The probability of capture upon attack, associated with passive selection, was higher for mussels than for scallops, since mussels can not swim to escape predators. Sea stars consumed few scallops when mussels were present, and so did not have a functional response on scallops (the target prey). Rock crabs exhibited prey switching: they selected mussels when scallop density was very low, did not select a certain prey type when scallop density was intermediate, and selected scallops when scallop density was high relative to mussel density. The interplay between encounter rate (associated with passive selection) and probability of consumption upon capture (associated with both active and passive selection) explained observed selection by crabs. Scallops were encountered by crabs relatively more often and/or mussels less often than expected from random movements of animals at all scallop densities. However, the probability of consumption varied with scallop density: it was lower for scallops than mussels at low and intermediate scallop densities, but tended to be higher for scallops than mussels at high scallop densities. When mussels were absent, crabs did not have a functional response on scallops, but rather were at the plateau of the response. When mussels were present with scallops at relatively low density, crabs exhibited a type II functional response on scallops. Our results have implications for the provision of protective refuges for species of interest (i.e., scallops) released onto the sea bed, such as in population enhancement operations and bottom aquaculture.     

Territorial behaviour of beaugregory damselfish (Stegastes leucostictus) in response to egg predators

To test the hypothesis that territorial male beaugregory damselfish (Stegastes leucostictus) can assess the degree of threat from egg predators, the aggressive behaviour of both males guarding eggs and males without eggs was recorded when they were presented with either one or five individuals of the wrasse egg predator Thalassoma bifasciatum. Presentations were made in a clear plastic bottle 0.5 m from artificial beaugregory breeding sites in the field. Two measures of aggressive behaviour (downhead threats and time spent within 10 cm of the presentation bottle) were significantly greater for multiple wrasse presentations than for single wrasse presentations, while a third measure (chase attempts) was not. In contrast, chase attempts were significantly greater for males guarding eggs than for males without eggs, but there was no significant difference in the level of downhead threats or bottle proximity time for this comparison. Levels of the three aggressive measures were not correlated with either the amount of eggs or the number of egg clutches present. These results indicate that territorial male beaugregories respond to an increase in the number of intruding egg predators by increasing the levels of low-cost threat behaviour, while the presence (but not the amount) of eggs results in an increase in the amount of higher cost attack behaviour. These experiments, therefore, support the hypothesis that male beaugregories can assess the degree of threat from egg predators, and indicate that they use this assessment to alter the strategies used in territorial defence.     

Behavioral plasticity of the soft-shell clam, Mya arenaria (L.), in the presence of predators increases survival in the field

Soft-shell clams, Mya arenaria, are sessile, suspension-feeding bivalves that are preyed upon by the exotic green crab, Carcinus maenas. Clams evade crab consumers by burrowing deeper into the sediment after perceiving a threat from a nearby predator. The purpose of this study was to determine the types of signals that M. arenaria use to detect predators and the types of behaviors clams use to avoid being eaten. In a field study, clams increased their burial depth in the presence of green crab predators consuming conspecifics that were caged nearby, and also increased burial depth after artificial tactile stimulation in the laboratory assay. These results indicate that clams can use chemical and mechanical cues to detect potential predatory threats. We performed a field study to examine the difference in survivability of clams that had burrowed deeper into the sediment in response to predators vs. control clams that were burrowed less deeply. Significantly higher survival rates were observed in clams that had initially burrowed more deeply, suggesting that increasing burial depth is a valid predator avoidance strategy. Some bivalves also alter their pumping rates in the presence of predators, making them less apparent and providing more structural defense by covering soft tissue, and we measured pumping time of soft-shell clams in the presence and absence of predators, when burrowing was not an option for escape. Soft-shell clams did not alter their pumping time in the presence of green crab predators, possibly because they employ a burrowing method called “hydraulic” or “jet-propelled” burrowing, where it is necessary for the clam to pump in order to burrow. Chemical signals and tactile cues instigated behavioral changes in M. arenaria, and this change in behavior (increasing burial depth) increased clam survival in the field.     

Reproductive costs of the symbiotic hydroid Hydractinia symbiolongicarpus (Buss and Yund) to its host hermit crab Pagurus longicarpus (Say)

Studies on the interaction between the hermit crab Pagurus longicarpus and its symbiotic hydroid Hydractinia symbiolongicarpus have focused on positive effects of hydroids on their host hermit crabs (e.g., protection from predators). Yet, these benefits may be balanced with reproductive costs, which are rarely studied. Results from field observations, laboratory trials, and a mesocosm experiment indicate that female hermit crabs in hydroid-colonized shells exhibit depressed ovigery, smaller clutch sizes, and increased clutch failure relative to females in bare shells. Frequent switching between bare and hydroid-colonized shells may alleviate negative effects when the density of hydroids in the environment is low, but at high densities Hydractinia may significantly impact hermit crab reproduction.     

Social behaviour of juvenile red sea urchins, Strongylocentrotus franciscanus (Agassiz)

This study examined social behaviour of juvenile red sea urchins, Strongylocentrotus franciscanus (Agassiz). At four coastal locations in British Columbia, Canada, distributions of juvenile sea urchins were examined in relation to adults. One-third of all juveniles were found underneath an adult “spine canopy”, another third outside the spine canopy but close to an adult, and the remainder were found apart from adults. Juveniles associated with adults were contagiously distributed with each other. In the laboratory, juveniles chose adults over other target locations. They selected adults in particular locations over others, and in one case showed selection among adults; but they did not select between fed and non-fed adults, nor between adults that had been “protective” and “non-protective” of juveniles in the field. In time-lapse film studies, starved juveniles showed little change in social behaviour when food was introduced, but showed a dramatic change in behaviour when predators were active. We suggest that juvenile red sea urchins are found under the spine canopies of adults as a result of juvenile behaviour; and that this interaction functions to protect juveniles from predation. The strong gregarious nature of juveniles among themselves may have evolved in a different selective situation as a defence against predation and to ensure reproductive success.     

Predation by Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) on immature Rhagoletis mendax Curran (Diptera: Tephritidae) in semi-field and field conditions

Practices that enhance abundance and diversity of generalist predators are often employed with the objective of improving biological control of insect pests. Ground beetles and other predators can prey on blueberry maggot, an important pest of blueberries, when mature larvae pupate in the ground. We conducted mesocosm and field experiments to determine if Pterostichus melanarius, a common predatory ground beetle, lowers maggot numbers in compost mulch or when predator and alternative prey abundances are manipulated. At background (field) densities of alternative prey, increasing densities of P. melanarius did not significantly reduce pest numbers in mesocosms containing compost or soil. When alternative prey were removed from compost, beetles reduced pest numbers by up to 35%. In field experiments, maggot numbers were higher when beetles and other predators were excluded from soil plots, but beetle exclusion had no effect in compost plots where both predator and alternative prey numbers were high. Our results indicate that there can be some reduction of blueberry maggot by P. melanarius and other potential predators when there are few alternative prey. However, despite attracting large numbers of predators compost mulch did not lead to a significant reduction in blueberry maggot; in fact, the high abundance of alternative food associated with compost appeared to interfere with beetle predation on blueberry maggot.     

Hunting behaviour of the perlid stonefly nymph Dinocras cephalotes (Plecoptera) under different light conditions

The hunting behaviour of Dinocras cephalotes nymphs was studied during two different light intensities, darkness and twilight (0·1 cd m^?2). Nymphs of the mayfly Baetis rhodani were provided as food. In darkness the predator moved slowly without stopping, encountering the prey with the antennae and the hair fringes on the tibiae. Little time was spent in a shelter. There was little tendency to pursue the prey after a missed first attack and the pursuing distance was short. In twilight the speed of the predator was higher and the movement was interrupted by long periods of rest. The number of successful attacks was higher and more attacks were initiated when the predator was immobile. Time of activity outside the shelter was short. There was a greater tendency to pursue the prey after a missed first attack and the pursuing distance was longer compared with that in darkness. There are two main advantages of changing strategy from ‘searcher’ in darkness to ‘ambusher’ in the light: to avoid being detected by predators hunting by vision and to avoid being detected by potential prey species relying on visual cues for the detection of predators. The optical design of the eye revealed that only those parts of the eye directed upwards and backwards were optimized to the light conditions at which the predator preferred to be active, suggesting that the main function of these areas is to detect predators, though an additional gain in detecting prey could also be seen.     

Type and nature of cues used by Nucella lapillus to evaluate predation risk

The ability of prey to detect and adequately respond to predation risk influences immediate survival and overall fitness. Chemical cues are commonly used by prey to evaluate risk, and the purpose of this study was to elicit the nature of cues used by prey hunted by generalist predators. Nucella lapillus are common, predatory, intertidal snails that evaluate predatory risk using chemical cues. Using Nucella and a suite of its potential predators as a model system, we explored how (1) predator type, (2) predator diet, and (3) injured conspecifics and heterospecifics influence Nucella behavior. Using laboratory flumes, we determined that Nucella responded only to the invasive green crab (Carcinus maenas), the predator it most frequently encounters. Nucella did not respond to rock crabs (Cancer irroratus) or Jonah crabs (Cancer borealis), which are sympatric predators but do not frequently encounter Nucella because these crabs are primarily subtidal. Predator diet did not affect Nucella responses to risk, although starved predator response was not significantly different from controls. Since green crabs are generalist predators, diet cues do not reflect predation risk, and thus altering behavior as a function of predator diet would not likely benefit Nucella. Nucella did, however, react to injured conspecifics, a strategy that may allow them to recognize threats when predators are difficult to detect. Nucella did not react to injured heterospecifics including mussels (Mytilus edulis) and herbivorous snails Littorina littorea, suggesting that they are responding to chemical cues unique to their species. The nature of cues used by Nucella allows them to minimize costs associated with predator avoidance.     

Maternal care in Gargaphia solani (Hemiptera: Tingidae)

We investigated the extent to which maternal behaviour exists in the lacebug Gargaphia solani as well as the adaptive relevance of maternal behaviour to predation, interspecific competition, feeding facilitation, and environmental heterogeneity. G. solani females aggressively defend their progeny against predators until maturity but provide no assistance in feeding, aggregating, or locating resources. In the absence of predators, nymphs suffer no ill effects if raised without their mother, but when nymphs are orphaned in normal field conditions only 3% survive to maturity. Such strong selection has given rise to maternal defensive behaviour that enables Gargaphia females to defend their progeny against predators.     

Reduction of attractiveness to the sea star Asterias forbesi (Desor) by the clam Mercenaria mercenaria (Linnaeus)

Both in field and laboratory choice tests, the sea star, Asterias forbesi (Desor), was attracted to distant upstream clams, Mercenaria mercenaria (Linnaeus). Clams exposed to upstream sea stars were chosen less frequently by downstream sea stars than clams without sea stars upstream. Sea stars neither attracted nor repelled downstream conspecifics.When clams were exposed to upstream sea stars, their oxygen consumption decreased, as did their pumping rate and activity (as measured by number of visible siphons). The former may result from one or both of the latter.It is concluded that clam and sea star sense each other over a distance by chemical cues. The response of the clam is a general lowering of activity which may result in decreased attractiveness to sea star predators. This response may serve as a defensive measure against distance detection by Asterias forbesi.     

Chemical and physical defenses against predators in Cystodytes (Ascidiacea)

Ascidians utilize both physical (spicules, tunic toughness) and chemical defenses (secondary metabolites, acidity) and suffer relatively little predation by generalist predators. The genus Cystodytes (Polycitoridae) is distributed widely in both tropical and temperate waters. Secondary metabolite composition, calcareous spicules and tunic acidity (pH < 1) may act as redundant defense mechanisms against predation in this genus. To assess the relative importance of chemical and physical defenses against predation in ascidians, we studied purple and blue morphs of Cystodytes from the western Mediterranean (formerly assigned to Cystodytes dellechiajei, but recently shown to belong to two different species), and a purple morph from Guam (USA), identified as Cystodytes violatinctus. Crude extracts, spicules, ascididemin (the major alkaloid of the blue morph) and acidity were used in feeding trials to evaluate chemical and physical defense mechanisms in Cystodytes spp. We performed feeding experiments in the field with a guild of generalist fish (mostly damselfish), and in the laboratory with a sea urchin and a puffer fish. Our results showed that all crude extracts and ascididemin significantly deterred fish predation, but not sea urchin predation. However, neither acidity alone nor spicules at natural concentrations deterred feeding. These results and other studies on sponges and gorgonians suggest that secondary metabolites are the primary means of defense against fish predators. Spicules and tunic acidity may perform other ecological roles and/or target certain specialist predators.     

Functional Response and Matrix Population Model of <Emphasis Type="Italic">Podisus nigrispinus</Emphasis> (Dallas, 1851) (Hemiptera: Pentatomidae) fed on <Emphasis Type="Italic">Chrysomya putoria</Emphasis> (Wiedemann, 1818) (Diptera: Calliphoridae) as Alternative Prey

Among the predators with high potential for use in biological control, the species of the genus Podisus (Hemiptera: Pentatomidae) have received special attention for laboratory rearing, since they feed on different agricultural and forestry pest insects. However, the type of diet offered to insects in the laboratory may affect the viability of populations, expressed essentially by demographic parameters such as survival and fecundity. This study assessed demographic and development aspects in experimental populations of Podisus nigrispinus (Dallas, 1851) fed on larvae of Chrysomya putoria (Wiedemann, 1818) (Diptera: Calliphoridae) as an alternative prey. The demographic parameters fecundity and survival were investigated in life stages of P. nigrispinus with ecological modeling, by applying the Leslie matrix population model, producing histograms of life stages in successive time steps. The functional response of P. nigrispinus was also investigated on seven densities of C. putoria third-instar larvae at 24 and 48 h. The survival of predators that reached adulthood was 65% and the development time from egg to adult was 23.15 days. The predator showed a type III functional response for consumption of C. putoria at 24 and 48 h. The Leslie-matrix simulation of the age structure provided perpetuation of the predator population over time steps and the prey proved to be feasible for use in rearing and maintenance of P. nigrispinus in the laboratory.