Predation of insects by feral cats (<Emphasis Type="Italic">Felis silvestris catus</Emphasis> L., 1758) on an oceanic island (La Palma,Canary Island)

Predation of insects by feral cats (Felis silvestris catus) on a heterogeneous oceanic island (La Palma, Canary Islands) was studied. A total of 127 invertebrates were identified in the analysis of 500 scats (100 from each habitat of the Island). Invertebrates appear in 18.00% of the scats, representing an insignificant percentage of the total consumed biomass by feral cats on La Palma Island (0.05%). Insects were the most common invertebrate prey both in percentage of occurrence (90.6%) and invertebrate biomass (93.53%), with a total of 115 prey items. Orthoptera, Lepidoptera and Coleoptera were the main prey groups. Among the five main habitats present in La Palma Island, the temperate forest shows the lowest consumption of invertebrates, although insect consumption did not show statistical differences. However Orthoptera and Lepidoptera were more frequently preyed on in the pine forest and in the xerophytic shrub, respectively. Moreover, applying the Simplified Morisita index, a different insect composition of the diet was observed among habitats. Although, none of insects predated by feral cats are threatened, the identification of invertebrate component of the feral cats’ diet is an important tool for the correct understanding of predation significance and to prevent damage to endangered insect species.     

Role of predation and parasitism in the extinction of the inoceramid bivalves: an evaluation

The inoceramid bivalves were dominant constituents of marine, epifaunal communities throughout the Late Mesozoic. They experienced a rapid decline in the Early Maastrichtian and virtually all taxa disappeared 1.5 Myr prior to the Cretaceous-Tertiary (K-T) boundary. The ultimate cause for their demise is still controversial. This study evaluates the role predation, parasitism and/or disease played in the evolution and extinction of Early Maastrichtian inoceramids from the Western Interior Seaway of North America (WIS). Escalation - the 'evolutionary arms race' between predators and prey - is said to be one of the most influential selective agents in evolution. Evidence of predation, parasitism, and disease in inoceramids is virtually undocumented prior to the Turonian. However, populations of inoceramids from the Late Cretaceous Pierre Shale show a marked increase in the number of individuals in which evidence for attempted predation and/or parasitism is preserved. The percentage of predation and/or parasitism steadily increases between the Baculites baculus and the B. grandis ammonite biozones (uppermost Campanian through Lower Maastrichtian) from 2.6% to values as high as 44.6%. The dramatic increase in shell deformities among inoceramids corresponds to a rapid radiation of shell-crushing brachyuran crabs and may be related to their activity. The introduction of new, efficient predators, such as brachyuran crabs, combined with parasitism and disease could have stressed inoceramid populations. Thus, they may have been more susceptible to environmental perturbations than under normal 'background' conditions. The disappearance of the inoceramids, at least from the WIS, may be one of the few cases where virtually an entire family lost the 'evolutionary arms race'.     

Borings in amphistegina (foraminiferida): Evidence of predation by floresina amphiphaga (foraminiferida)

The small foraminifer, Floresina amphiphaga, preys upon the relatively large foraminifer, Amphistegina gibbosa, leaving 2–10 characteristic predation holes in the test of the prey.     

Response by coccinellids to spatial variation in cereal aphid density

The objectives of this study were to determine if coccinellids adjusted their distribution within spring wheat fields in response to spatial variation cereal aphid density in the fields and to describe the patterns of cereal aphid population growth that resulted. Field experiments were completed in which the physical dimensions of patches infested with cereal aphids, cereal aphid density, and access to patches by coccinellids were varied. Aphid infestations consisted of naturally occurring densities (natural patches) and much greater densities created by supplementing patches with aphids (supplemented patches). Coccinellids were denied access to some supplemented patches (exclusion patches) but allowed unlimited access to others. Densities of adult Hippodamia convergens and Coccinella septempunctata were correlated with aphid density in patches whereas density of Coleomegilla maculata was not. Aggregation by coccinellids was independent of patch area. The realized aphid population growth rate (r) was lower in supplemented than natural patches in all four trials but was significantly lower in only one trial. The lower r in supplemented patches was not exclusively caused by coccinellid predation, and emigration of aphids from patches probably also contributed. r was significantly greater in exclusion patches than supplemented and natural patches, indicating that coccinellids markedly reduced aphid numbers in patches even when aphid density was extremely high. Received: February 17, 1999 / Accepted: February 1, 2000     

A test for top-down cascade in a detritus-based food web by litter-dwelling web spiders

A top-down cascade in detritus-based food webs has the potential to alter ecosystem functioning but its prevalence in terrestrial systems remains unclear. We manipulated the density of the dominant web spider Neriene brongersmai for 1.5 years to see whether the cascading effect would propagate down to the litter decomposition rate in the forest-floor of a Japanese cedar forest. Decreasing spider abundance increased collembolan density, but it did not change the biomass of microorganisms or the litter decomposition rate. We propose possible explanations for the absence of a top-down cascade and discuss the difficulty in generalizing the presence and absence of a cascading effect in soil ecosystems.     

Massive leaping of Sardinella aurita valenciennes, 1847 under probable risk of predation in Northern Aegean sea (Greece)

On the morning of 15th December 2002, several hundred live round sardinella (Sardinella aurita) individuals leaped out of the water and became stranded on the breakwater of Nea Iraklitsa port (Kavala Gulf, northern Aegean Sea, Greece). The phenomenon was most likely caused by the attack of the cetacean predator Tursiops truncatus (bottlenose dolphin), which is abundant in the area and feeds upon pelagic fish. The ability of round sardinella to leap out of the water has never been reported for other pelagic fishes.     

Habitat use and feeding behavior of thirteen species of benthic stream fishes

Synopsis The densities, habitat use, and feeding behaviors of 13 fish species belonging to the benthic invertebrate-feeding guild were studied by snorkeling at three localities in the Little River of eastern Tennessee, U.S.A. Resource partitioning occurred by habitat, feeding behavior and time of activity. Differences were also found at the generic level.Cottus was a nocturnal feeder, whereasPercina andEtheostoma were, for the most part, diurnally active.Percina moved about rapidly and spent most of its time above the bottom. In contrast,Etheostoma varied considerably in the amount of time spent under cover, spent little time above the bottom, and exhibited low levels of swimming activity. Nearly all species sought cover at night, suggesting they may be particularly sensitive to predation at night. Species with small adult sizes (Etheostoma, Cottus andP. evides) were concentrated in shallow water habitats, whereas species with large adult sizes (Percina) were more abundant in deep water habitats. The habitat use data are consistent with the hypothesis that size-selective predation by centrarchid bass may cause smaller fish to avoid deep water areas. Large species should have a lower risk of predation due to their size and behavior.     

Effect of an invasive crab upon a marine fishery: green crab, Carcinus maenas, predation upon a venerid clam, Katelysia scalarina, in Tasmania (Australia)

Nonindigenous species are increasingly recognized as altering marine and estuarine communities, causing significant changes in abundance and distribution of native species. Such effects are of particular concern to coastal fisheries. We experimentally determined the effect of the nonindigenous European green crab, Carcinus maenas, upon the stepped venerid clam, Katelysia scalarina, the basis for a fledgling clam fishery in Tasmania, Australia. First, we observed a trend of decreased juvenile (<13-mm shell length or SL) abundance of K. scalarina at sites with C. maenas relative to those without this invasive predator. Additionally, relative predation intensity on these juveniles was significantly higher in invaded areas. To better understand the dynamics of predation by this invader, we conducted a number of manipulative experiments. In cage experiments testing per capita predation rates, we found that: (1) of the various sizes of C. maenas, large C. maenas were the most significant predators; (2) the smallest size class of K. scalarina tested (6-12-mm SL) was preferred by C. maenas; (3) C. maenas had much higher predation rates than any native predator tested; and (4) while the native shore crab, Paragrapsus gaimardii, was found to have a constant predation rate over an eightfold range of densities of juvenile K. scalarina (16-128 individuals·m⁻²), C. maenas significantly increased its per capita predation with increasing prey density. Notably, in open field plots at a site where C. maenas was abundant, predation was constant over the range of tested prey densities. We predict, therefore, that the invasion of C. maenas will have significant negative consequences for the Tasmanian K. scalarina fishery.     

Can Fish Control Planthopper and Leafhopper Populations in Intensive Rice Culture?

Planthoppers and leafhoppers are important rice pests. We tried to find out whether a polyculture of silver barb, common carp and Nile tilapia could control hoppers in intensively cropped rice fields. We used the data of five rice-fish experiments conducted between 1995 and 1998 at the Co Do rice-fish research station, Can Tho province, Mekong Delta, Vietnam. Our results showed that the number of Nilaparvata lugens (Stål), Sogatella furcifera (Horváth), Nephotettix virescens (Distant) and Recilia dorsalis (Motschulsky) was the same in fields with and without stocked fish. We concluded that the three stocked fish species are not able to control hopper numbers. Other, predatory fish species might be more effective in hopper control.     

Generalist caterpillar prey are more palatable than specialists for the generalist predator Iridomyrmex humilis

Summary Experiments are described which test the hypothesis that more host-specific species of caterpillars should be less aceptable to a generalist predator than polyphagous species. Caterpillars of all species were tested in paired choice tests with the Argentine ant, Iridomyrmex humilis. Experiments were replicated ten times, videotaped and later analyzed. Brightly colored specialist species (normally considered to be aposematic) were clearly the least palatable, while more cryptic specialists were also significantly less acceptable than generalists overall. Leaf-tying species were considered separately; all were highly palatable independent of host range. The results indicate that among caterpillars that do not construct leaf shelters, those with a wide post range are more acceptable than those with a narrow host range. This is consistent with the notion that generalist predators provide selection pressure favoring narrow host range in their herbivorous prey.