Reduction In Predation Research Articles

Reduction of Sea Star Predation by the Burrowing Response of the Hard Clam Mercenaria mercenaria (Mollusca: Bivalvia)

The hard clam Mercenaria mercenaria burrows deeper into the sediment when the predaceous sea star, Asterias forbesi is present. The supposition that this increase in burial depth represents an escape response designed to reduce predation was tested experimentally by regulating clam burial depth through manipulation of the amount of sediment available for burial. Mercenaria maintained at zero depth were eaten by Asterias at greater rates than those held at ordinary burial depths (2.5–3.0 cm). These clams in turn were eaten at greater rates than those maintained at escape depths (4.0–4.5 cm). The results unambiguously establish an anti-predator function for the burrowing response, as well as underscoring the protective function of the fossorial habit. They are not confounded by behavioral predator food preferences, inherent differences between prey species, or debilitating side effects of preventing prey from escaping. Mechanisms by which the burrowing response may reduce predation are discussed and observations on the unreported clam-digging behavior of Asterias forbesi are presented.

Food Deprivation in the Muricid Drill Ocinebrina edwardsi (Mollusca: Prosobranchia): Histomorphological and Behaviour Research

. After a starvation period the predation rate in specimens of Ocinebrina edwardsi is less than in animals which feed normally. The closer the prey predator contact during the starvation period, the higher the level of predation when the snails are allowed to resume feeding. The reduction in predation after a long or short fast is obviously the result of changes in the structure and function of the ABO. In the secreting cells of normally fed animals the following enzymatic activities can be distinguished: acid and alkaline phosphatases, carbonic anhydrase and ATPase. Carbonic anhydrase and acid phosphatase activities are not present in starved individuals. Only after the animals have resumed feeding for 10 days does the ABO completely recover its enzymatic functions.

Mathematics and Mallard Management

Waterfowl managers can effectively use simple population models to aid in making management decisions. We present a basic model of the change in population size as related to survival and recruitment. A management technique designed to increase survival of mallards (Anas platyrhynchos) by limiting harvest on the Chippewa National Forest, Minnesota, is used to illustrate the application of models in decision making. The analysis suggests that the management technique would be of limited effectiveness. In a 2nd example, the change in mallard population in central North Dakota is related to implementing programs to create dense nesting cover with or without supplementary predator control. The analysis suggests that large tracts of land would be required to achieve a hypothetical management objective of increasing harvest by 50% while maintaining a stable population. Less land would be required if predator reduction were used in combination with cover management, but questions about effectiveness and ecological implications of large scale predator reduction remain unresolved. The use of models as a guide to planning research responsive to the needs of management is illustrated. J. WILDL. MANAGE. 43(1):18-35 Management of a wildlife population is a complicated task that often requires decisions based on limited data. To make logical decisions we need (1) a management policy or objective defined in terms of some goal, (2) a relationship between that goal and parameters of the population to be managed, and (3) estimates of these parameters. Such a relationship is often termed a model, and can be either quite rudimentary and qualitative or complicated and quantitative. Inadequate information often forces us to use models that grossly oversimplify the behavior of the real population and to employ estimates that are frequently little better than informed guesses. The manager cannot postpone a decision until the dynamics of the population are fully understood and precise estimates of all parameters are available. Inaction is in fact a decision by default. The development of simple models, imperfect though they may be, and the graphic representation of these models can facilitate logical and orderly development of management strategy. Because of the large quantity of pertinent banding and survey data available, the mallard has been the subject of several published models (Walters et al. 1974, Anderson 1975a,b, Brown et al. 1976). These models use estimates of production based on survey data for the continental population. In contrast, our model relates recruitment to various components that are frequently measured in local studies and that are subject to manipulation by the waterfowl manager. The exercise of presenting a model has a number of benefits: (1) inspection of the model may focus attention on critical parameters; (2) the model provides a frame of reference for evaluating policy and assessing the feasibility of objectives; (3) insight into possible alternatives for reaching an objective is gained; and (4) we are forced to face the reality of the management problem and to answer important questions such as cost effectiveness and political feasibility. The purpose of this paper is to demonstrate a simple model that can facilitate decisions concerning management of mallards in the north central

Predation on Hard Clam (Mercenaria mercenaria) Populations

Abstract Predation on hard clams (Mercenaria mercenaria) was examined in laboratory experiments and in wild populations. Increases in clam density following predator reduction was also examined. The principal predators of hard clams are gastropods and crabs, which take mostly small clams. In the laboratory, crabs consume clams rapidly. Wild populations of clams are most abundant in areas where either predators are scarce or stones provide cover from them. Variations in recruitment and predation on clams smaller than about 15 to 20 mm determine the strength of year classes. As clams grow, they become less vulnerable to a succession of predators, first outgrowing mud crabs at a length of about 7 mm, rock crabs at about 15 mm, oyster drills at about 20 mm, and moon snails at about 50 mm. Clam densities were seven and eight times as great in sections of shellfish beds where predators were reduced by pesticide applications compared with untreated sections of the same beds.

Destruction of kelp-beds by sea-urchins: A cyclical phenomenon or irreversible degradation?

A stable kelp bed ecosystem in St. Margaret's Bay, Nova Scotia (Canada), had as its main producersLaminaria longicruris andL. digita. Most algal production was exported as detritus, but there was a moderate population of herbivores, mainly the sea urchinsStrongylocentrotus droebachiensis. These were eaten by crabs,Cancer irroratus and by lobsters,Homarus americanus. Lobsters also preyed on crabs. Beginning in 1968, sea urchins became locally abundant and overgrazed the kelp beds, converting large areas to urchindominated barren grounds. Almost all kelp beds in St. Margaret's Bay (140 km2) have now been destroyed. During the same period, lobster biomass decreased, and the hypothesis was put forward that reduction in lobster predation led to increased urchin abundance and kelp bed destruction. Evidence is presented for the hypothesis that urchin-dominated barren grounds are a new, stable configuration of the ecosystem, and that a long-term decrease in primary and secondary productivity of these coastal waters can be expected.

Upland Duck Nesting Related to Land Use and Predator Reduction

Upland Duck Nesting Related to Land Use and Predator Reduction

Effects of aldicarb applied side-dress to cotton on some arthropods in the Monroe County, Mississippi, boll weevil diapause-control area in 1969.

The effects of aldicarb on boll weevils, Anthonomus grandis Boheman; Heliothis larvae; and beneficial predators was investigated in large fields of cotton with and without boll weevil sex-attractant traps. Three of the fields in the Monroe County, Miss., boll weevil diapausecontrol area had boll weevil sex-attractant traps, and with 2 lb (0.9 kg) active ingredient of aldicarb applied as a side-dress application to cotton in the pin-head square stage, season-long boll weevil control was obtained. Three aldicarb-treated fields without boll weevil sex-attractant traps had 39 days of boll weevil control. Heliothis larvae became an economic problem earlier in the aldicarb-treated fields than in the control fields. Predator reduction was drastic in the aldicarb-treated fields after the first rain. The predator population generally increased in the control fields until they were treated for control of Heliothis larvae or boll weevils later in the season.

Some aspects of adaptation in a polymorphism for breeding colours in the Threespine stickleback (Gasterosteus aculeatus))

Polymorphism in the nuptial colouration of male Threespine sticklebacks (Garterosteus aculeatus L.) was studied. In Lake Wapato in Eastern Washington, approximately 14% of the breeding males develop typical red nuptial colouration while others develop various colours which were grouped into a non‐red category. The hypothesis was tested that red males are adaptive in Lake Wapato as a result of sexual selection and differential egg predation.In a series of mate preference tests, females demonstrated a significant preference for red males over non‐red males. In a second experiment, using artiticially coloured non‐red males, it was shown that the females are responding to the red colouration alone. This evidence suggests that one of the selective pressures maintaining the red morph is sexual selection.In a stomach analysis of male and female sticklebacks collected from a breeding colony it was found that 51 % of the fish examined had stickleback eggs in their stomachs. Both male and female sticklebacks eat a large number of eggs; however, males eat significantly more eggs than females. Eggs were found to be most susceptible to predation during their first four days of development. Given that red ventral colouration has threat value, red males may also be adaptive because of a reduction in egg predation within their territories in contrast to non‐red males.One of the selective forces against red males is probably differential predation by trout (Salmo gairdneri). This trout predation has been shown to be extensive in Lake Wapato. The opposing selective forces discussed in this paper cannot maintain the polymorphism; they are only components of fitness of the colour morphs.

Population changes within a group of fish species in Lake Tanganyika following their exploitation

Pelagic fish populations in Lake Tanganyika consist mainly of two small clupeid species and four centroponiid species which prey on them. Exploitation with purse‐seines began in the southeast arm in 1962 and catches were sampled up to early 1969. Inshore clupeid populations were also sampled with a scoop‐net (lusenga of the kind used in the traditional inshore fishery.Clupeid biomass reached annual maxima around September. One clupeid species, Stolothrissa tanganicae Regan, dominated pelagic catches except in 2 years when about equal quantities of the other clupeid, Limnothrissa miodon Blgr. were caught. Numbers of each predator (three species of Lates and Luciolates stappersii Blgr.) decreased from 1963 to 1966 and remained low thereafter. The clupeid catch rose from 1964 to 1967 and remained high in 1968. The average nightly catch weight per year of all species together altered relatively little. Changes in population size distributions occurred.Sampling methods were concluded to be valid for clupeid populations, but probably indi‐cated only general changes in predator populations. Clupeid life‐cycles are mostly accomplished within a year, and appear closely related to the periodic and spatial variations in plankton production. The two species are competitive and can replace one another in the pelagic zone. Certain distribution patterns of the clupeids and of the predator young are believed to be adaptations to severe predation. Low replacement rates under fishing pressure account for the decline of predator species, and the clupeid increase resulted from reduction in predation. A fairly stable exploited phase has apparently been reached in which clupeid biomass is much greater and predator biomass much less than in the natural state. The data encourage certain predictions. Similar major trends occurred in the much larger fishery in the Burundi sector of the lake.

Results of Predator Reduction on Brook Trout and Brown Trout in 4.2 Miles (6.76 km) of the North Branch of the Au Sable River

Abstract During the autumns of 1964, 1965 and 1966, brown trout 12.0–25.1 inches (305–638 mm) in length were removed from 4.2 miles (6.76 km) of the North Branch of the Au Sable River (Dam 2-County Line), and American mergansers were harassed in the same area each winter as time permitted. The objective was to decrease losses among the smaller salmonids which would otherwise be eaten by the large trout and mergansers. Effects of control efforts were assayed by comparison of 1965–1967 angling results and population estimates with similar data accumulated on the test section and two other stream sections of the North Branch during 1961–1964 when predator manipulation was not carried on. In 1964, 561 large brown throut (66% of the estimated population) were removed. In 1965 and 1966, the actual removals were 346 and 104, or 63 and 40% of the population, respectively. The only major change noted was an increase during 1965, 1966 and 1967 in numbers of brook trout larger than 9 inches (229 ram) in the populati...

Eruption of Ungulate Populations, with Emphasis on Himalayan Thar in New Zealand

An eruptive fluctuation is defined operationally as an increase in numbers over at least two generations, followed by a marked decline. Reported eruptions in ungulates suggest that the upswing is initiated by a change in food or habitat and is terminated by overgrazing. An apparent exception–the Kaibab eruption–probably also fits this pattern. The interpretation causally linking reduction of predators on the plateau with increase of deer is an overstatement of evidence. Eruption of established populations is essentially the same process as the buildup of populations initiated by liberation, with the difference that in the second case a zone of high density migrates radially from the point of liberation. Eruption of thar (a goat—like bovid) after liberation in New Zealand was studied by sampling populations at different distances from the point of liberation. The aim was to determine trend of demographic statistics across an eruptive fluctuation that spans 50 years. Although fecundity varied across the eruption, the major influence on rate of increase was traced to variation in death rate. The major component of this variation was the rate of mortality over the first year of life. Trend in death rate, and hence in rate of increase, was associated with trends in other population statistics that are easier to measure. The most useful correlative of rate of increase is probably the level of fat reserves. While we do not know whether trends in population statistics of thar reflect those of other ungulates during an eruptive fluctuation, the generality of the reported trends may usefully serve as a testable hypothesis.

Saqueo y depredación de nidadas de tortugas marinas, durante las temporadas 2003 a 2012, en seis playas del Golfo de Paria, Venezuela

Poaching and predation of sea turtle clutches, during the 2003 and 2012 seasons, on six beaches of the Paria Gulf in Venezuela. Looting and predation of nests are among the major threats to marine turtles. Six beaches of Paria Gulf, northeastern Venezuela, have been protected and had a reduction of clutch poaching and predation on leatherback (Dermochelys coriacea), green (Chelonia mydas), and hawksbill (Eretmochelys imbricata) turtles. During ten years (2003-2012) of nesting seasons (March through October) the six beaches were observed for nesting, poaching and predation. The most frequent losses are caused by poaching, followed by the common fox (Cerdocyon thous), opossum (Didelphis marsupialis) and tamandua (Tamandua tetradactila). The most poached beach is Silvano, followed by Los Garzos (main nesting beach at the site) and Cerezo, which is more distant from the conservation team activity.

The microdistribution and social behavior of some pelagic mysid shrimps

Certain pelagic mysids occur in well defined layers near the sea floor in bathymetric zones roughly parallel with shore, within which, during the day, they form large shoals composed of smaller swarms and schools. When light is present vision is apparently the primary, but not exclusive, mode of establishing contact between individuals. Aggregation occurs at night in field populations. Experiments showed that parallel swimming orientation occurs in total darkness but is less precise. At night the mysids probably respond to body contact and the currents created by their fellows; the possible role of general chemical cues in promoting aggregation was not established. Copulation occurs only at night. Apparently it involves emission of a specific chemical attractant by molting adult females, to which only adult males of the same species respond. The observations are interpreted in relation to microdistribution and to possible functions, which include: maintenance of position in the habitat, reduction of predation, efficiency of copulation, and population regulation. It is concluded that studies of structure and function of pelagic populations and communities must take sociality into account.

Effect of Predator Reduction on Waterfowl Nesting Success

Effect of Predator Reduction on Waterfowl Nesting Success

THE FUNCTIONAL BASIS OF SOME BEHAVIOUR IN THE WOODPIGEONCOLUMBA PALUMBUS

SUMMARYSome behaviour observed in a wild Woodpigeon population is described. During the winter, October‐February, the species is gregarious. Flocks roost and feed together but each bird maintains its own individual distance. On the feeding grounds intra‐specific competition is apparent, supplanting attacks and actual fighting occurring. Gregariousness is discussed, mainly in relation to the white wing‐ and neck‐markings, and is considered to serve the function of improving food exploitation.The development of territorial display from early spring to the main breeding season is described. Most birds were territorially active in mid‐July. There were many active males in May which appeared potentially capable of breeding, but which did not then breed. It is shown that the proportion of the day spent in territorial and other display increases towards the beginning of the main egg‐laying season. Territorial defence is undertaken by both sexes.The bowing display is the initial sexual advance of the male to the female. It contains display elements typical of the nest calling display and these in turn are related to nest building movements. The display is very suitable for appeasement and can arise during periods of aggressive conflict. Bowing displays are frequently given at a distance from the territory, especially on the feeding grounds.Nest calling is a submissive display, mainly shown by the male and is used to attract the female to the nest or potential nest site. Caressing can occur at the same time as nest calling or away from the nest, and possibly evolved from the food begging movements of the nestling. It usually precedes courtship feeding. On the physical level the display is used to stimulate ovulation in the female, so that when used for long periods in the absence of courtship feeding it appears as a ritualized display. Courtship feeding and copulation are discussed.The periods during the day when both sexes were present at the nest site were limited and occurred at around 07.00–9.00 and 15.00–17.00 hours (G.M.T.).During incubation the male attends the nest from about 10.00–17.00 hours (G.M.T.), the female sitting during the rest of the 24 hours. This gives the male nine hours and the female seven hours feeding time during the main breeding season. Although sufficient at such times it appears to be inadequate earlier in the year when the incubation routine is affected to the extent that nests are left unguarded. A higher predation rate on eggs results.When brooding small young the adults take turns as during egg incubation. Nestlings are fed at frequent intervals, usually when they beg for food, but the adults also initiate such behaviour. Later, when the squabs are no longer continuously brooded, they are visited by each adult only twice a day. The physiological adaptations of the method of feeding the young are discussed.The possible functions of the territory are reviewed and it is concluded that dispersal with consequent reduction in egg predation is the most important function served.The significance of the diurnal activity rhythms, which are a feature of all the breeding stages, is discussed. It is suggested that the food supply could act directly in determining the duration of sexual displays, which in turn could provide the final stimulus regulating the onset of breeding.

Interaction of Natality, Mortality and Movement during One Annual Cycle in a Microtus Population

A population of meadow mice, Microtus pennsylvanicus, was studied through one annual cycle, near East Lansing, Michigan. In May the mice were at a very low density and living under good conditions of food and cover and experiencing little competition. Because of high natality the population increased rapidly throughout the summer and fall. Breeding ceased in January, and the population continued to increase in February as a result of immigration. Mortality was highest in the summer and least in the winter. This was the result of (1) change in the age composition of the population, and (2) probable reduction of predation due to a persistent snow cover. A life table showed that mortality was highest in the postnestling juveniles and young adults. In other age classes mortality continued at approximately 50 per cent. The natural rate of increase of the population was -0.0315 daughters per female per day. Although the rate of increase was negative, immigration was sufficient to cause the population to increase in size. Although the population dynamics of meadow mice of the genus Microtus has been the subject of considerable research both in North America and Europe, our knowledge of the interaction of mortality, natality, and movement in a single population of this genus is still far from complete. In this paper I intend to present a detailed analysis of these factors in a population of Microtus pennsylvanicus. The data for this analysis were obtained during an intensive one and one-half year investigation of the energy flow through an old-field vegetation Microtus pennsylvanicus -Mustela rixosa food chain. (Golley, 1960). My studies were made in 1956 and 1957 in an abandoned field near the Michigan State University campus, East Lansing, Michigan. Blue grass (Poa compressa), wild carrot (Dauca carota) and Canada thistle (Cirsium arvense) were the chief dominants in the vegetation. Since occasional burning was the only disturbance to the vegetation for about 15 years prior to the study, a dense sod of grasses and perennial herbs had developed and provided an abundance of cover and food for the meadow mice. During the study period the weather was unusually mild. The temperature was above average in every month except September, 1956, and January, 1957, and precipitation was below average throughout 'the fall and winter. The setudy area was surrounded on four sides by orchards, alfalfa fields, and old-field vegetation, all of which furnished habitat for Microtus. Acknowledgments.-I am grateful to Dr. Don W. Hayne, Fish and Wildlife Service, for his advice on methodolgy and analysis of the data on density, natality and mortality. I am also grateful to Dr. Helmut K. Buechner, Dr.

Differential Food Selection by Moray Eels and a Possible Role of the Mucous Envelope of Parrot Fishes in Reduction of Predation

Differential Food Selection by Moray Eels and a Possible Role of the Mucous Envelope of Parrot Fishes in Reduction of Predation