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Egg Predation (egg + predation)

Distribution by Scientific Domains

Life Sciences	70%
Earth and Environmental Science	30%

Selected Abstracts

Effects of air pollution on natural enemies of the leaf beetle Melasoma lapponica

JOURNAL OF APPLIED ECOLOGY, Issue 2 2000
Elena L. Zvereva
Summary 1. ,Air pollution might have differential effects on herbivores and their natural enemies, thus changing population dynamics. Therefore, from 1993 to 1998 we studied mortality caused by parasitoids and predators to the willow-feeding leaf beetle Melasoma lapponica in the impact zone of the Severonikel nickel,copper smelter (Kola Peninsula, north-western Russia). 2. ,Densities of M. lapponica were very low at clean forest sites (below five beetles per 10-min count) but higher in polluted areas (10,340 beetles per count). There were, however, variations between study years. 3. ,Egg predation, mainly by syrphid larvae and zoophagous bugs, was higher at relatively clean sites (55·3%) than at polluted sites (22·2%). Similarly, predation on larvae by zoophagous bugs and wood ants was higher at clean sites (68·4%) than at polluted sites (32·9%). 4. ,In contrast to predation, mortality caused by the parasitoid flies Megaselia opacicornis (Phoridae) and Cleonice nitidiuscula (Tachinidae) was lower at clean sites (12·3%) than at polluted sites (35·3%). Total parasitism levels increased significantly with pollution load. 5. ,Total mortality caused by natural enemies was higher at clean sites (93·7%) than at polluted sites (79·4%) due to higher predation rates, which may partly explain increased leaf beetle density within the smelter's impact zone. The effects of predators in clean forests were confirmed by the extinction of adults of M. lapponica introduced to one of the forest sites. 6. ,Although some individual sources of mortality appeared to be density dependent (direct or inverse), the joint effect of all natural enemies was not. 7. ,Our data show that a decrease in predation can contribute to increased leaf beetle density at polluted sites. However, the overall effects of natural enemies in this case were not sufficient to account for all density variations between sites. To our knowledge this is the first study to assess how pollution affects the partitioning of mortality in herbivorous insects between predators and parasitoids. [source]

The possible adaptive advantages of terrestrial egg deposition in some fluvial diadromous galaxiid fishes (Teleostei: Galaxiidae)

FISH AND FISHERIES, Issue 3 2006
RM McDowall
Abstract Several diadromous New Zealand and Australian species of Galaxias are now known, or suspected, to deposit their eggs amongst riparian vegetation or substrates either supratidally in estuaries or in forested streams in locations that are only temporarily submerged by elevated water levels. The eggs develop in a humid atmosphere and hatch when the egg deposition sites are resubmerged; a significant role for agitation in stimulating hatching seeming likely. There are risks from the eggs becoming dehydrated, and also from a failure by water to resubmerge the eggs before they have exhausted their energy resources. Hatching is triggered by elevated flows, perhaps being an outcome of agitation of the eggs. Elevated flows may also increase the rate of downstream transport of the larvae, facilitating survival during dispersal to sea from spawning sites in streams that may be long distances inland. Hatching during flood events may favour survival of the larvae because turbid flows may provide ,cover' for the larvae as they emigrate to sea. Risks from egg predation by aquatic predators may be replaced by risks from terrestrial predators. [source]

Distribution, seasonal use, and predation of incubation mounds of Orange-footed Scrubfowl on Komodo Island, Indonesia

JOURNAL OF FIELD ORNITHOLOGY, Issue 2 2009
M. Jeri Imansyah
ABSTRACT Megapodes are unique in using only heat from the environment, rather than body heat, to incubate their eggs as well as the precocious independence of their chicks on hatching. Of 22 recognized species of megapodes, 9 are listed as threatened due to factors including habitat loss and fragmentation, and predation on eggs and chicks. Orange-footed Scrubfowl (Megapodius reinwardt) are conspicuous components of the Oriental/Austral avifauna that inhabit the monsoon forests of the Lesser Sunda chain of islands in Indonesia. We examined the abundance, patterns of distribution, physical characteristics, seasonal activity, and predation risk of incubation mounds of Orange-footed Scrubfowl on Komodo Island in eastern Indonesia. We surveyed 13 valleys on Komodo Island from April 2002 to January 2005 and located 113 tended and 107 untended incubation mounds. Densities of scrubfowl mounds in our study were similar to that reported by investigators during the 1970s, suggesting little change in the scrubfowl population since then. Most scrubfowl mounds were on sandy or loamy soils in open monsoon forest with little overhead shade, and placement of mounds in such areas may ensure adequate temperatures for egg incubation. Although some mounds were tended during all months, mound use peaked during the late wet season in March. During the dry season (April,November), only a few mounds were tended. Komodo dragons (Varanus komodoensis) and wild pigs (Sus scrofa) were the primary predators of scrubfowl eggs, with no indication of egg predation by humans. The valley with the largest number of untended mounds in our study also had the largest number of active Komodo dragon nests. This suggests an effect of Komodo dragons on scrubfowl numbers, but additional study is needed. SINOPSIS Los Megadopodos son únicos al usar calor del ambiente, en vez de calor corporal, para incubar sus huevos, y que sus polluelos nidífugos son independientes después de la eclosión. De las 22 especies de Megapodos reconocidas, nueve están en la lista de especies amenazadas debido a factores como pérdida y fragmentación del hábitat y depredación de huevos y polluelos. Megapodius reinwardt es un componente conspicuo de la avifauna Oriental/Austral que vive en los bosques monzones en las islas de las Sundas Menores en Indonesia. Examinamos la abundancia, patrones de distribución, características físicas, actividades temporales y riesgo de depredación en los montículos incubadores de M. reinwardt en la isla de Komodo en el este de Indonesia. Examinamos 13 valles en la isla de Komodo entre Abril 2002 y Enero 2005 y localizamos 113 montículos incubadores atendidos y 107 que no estaban siendo atendidos. Las densidades de montículos de M. reinwardt en nuestro sitio de estudio fueron similares a los reportados por investigadores en la década de los ,70, lo cual siguiere pocos cambios en la población de M. reinwardt desde entonces. La mayoría de los montículos de M. reinwardt se encontraron en suelos arenosos o margosos en bosques monzones abiertos, con poca cobertura de vegetación, y la localización de los montículos en estas áreas posiblemente aseguran temperaturas adecuadas para la incubación de los huevos. A pesar de que algunos montículos estuvieron atendidos durante todos los meses, el pico de uso de los montículos ocurrió durante el final de la temporada de lluvias en Marzo, y durante la temporada seca (Abril,Noviembre) solo algunos montículos estuvieron atendidos. Los dragones de Komodo (Varanus komodoensis) y los cerdos salvajes (Sus scrofa) fueron los principales depredadores de los huevos de M. reinwardt, y no hubo indicio de depredación por humanos. En nuestro estudio el valle con los mayores números de montículos desatendidos tenía el mayor número de nidos activos de dragones de Komodo. Este resultado sugiere la posibilidad de algún efecto de los dragones de Komodo en los números de Megapodius reinwardt, pero estudios adicionales son requeridos. [source]

Effects of nest-site characteristics and parental activity on cowbird parasitism and nest predation in Brown-and-yellow Marshbirds

JOURNAL OF FIELD ORNITHOLOGY, Issue 1 2009
Walter S. Svagelj
ABSTRACT Nest-site selection and nest defense are strategies for reducing the costs of brood parasitism and nest predation, two selective forces that can influence avian nesting success and fitness. During 2001,2002, we analyzed the effect of nest-site characteristics, nesting pattern, and parental activity on nest predation and brood parasitism by cowbirds (Molothrus spp.) in a population of Brown-and-yellow Marshbirds (Pseudoleistes virescens) in the Buenos Aires province, Argentina. We examined the possible effects of nest detectability, nest accessibility, and nest defense on rates of parasitism and nest predation. We also compared rates of parasitism and nest predation and nest survival time of marshbird nests during the egg stage (active nests) with those of the same nests artificially baited with passerine eggs after young fledged or nests failed (experimental nests). Most nests (45 of 48, or 94%) found during the building or laying stages were parasitized, and 79% suffered at least one egg-predation event. Cowbirds were responsible for most egg predation, with 82 of 107 (77%) egg-predation events corresponding to eggs punctured by cowbirds. Nests built in thistles had higher rates of parasitism and egg predation than nests in other plant, probably because cowbirds were most active in the area where thistles were almost the only available nesting substrate. Parasitism rates also tended to increase as the distance to conspecific nests increased, possibly due to cooperative mobbing and parental defense by marshbirds. The proportion of nests discovered by cowbirds was higher for active (95%) than for experimental (29%) nests, suggesting that cowbirds used host parental activity to locate nests. Despite active nest defense, parental activity did not affect either predation rates or nest-survival time. Thus, although nest defense by Brown-and-yellow Marshbirds appears to be based on cooperative group defense, such behavior did not reduce the impact of brood parasites and predators. RESUMEN La selección del sitio de nidificación y defensa del nido son estrategias que reducen los costos del parasitismo de cría y predación de nidos, dos fuerzas selectivas que pueden afectar el éxito reproductivo y la eficacia biológica de las aves. Durante 2001,2002, analizamos el efecto de las características del sitio de nidificación, patrón de nidificación, y actividad parental en la predación de nidos y parasitismo de cría por tordos (Molothrus spp.) en una población de Pseudoleistes virescens en la provincia de Buenos Aires, Argentina. Examinamos los posibles efectos de la detectabilidad, accesibilidad y defensa del nido en las tasas de parasitismo y depredación de nidos. Asimismo, se compararon las tasas de parasitismo, depredación, y tiempo de supervivencia de los nidos entre los estadios de huevo (nidos activos) con los de los mismos nidos cebados artificialmente con huevos de passerinos (nidos experimentales). La mayoría de los nidos (45 de 48, o 94%) hallados durante los estadios de construcción y puesta fueron parasitados, donde el 79% de los nidos sufrieron al menos un evento de predación de huevos. Los tordos fueron responsables de la mayoría de los eventos de predación de huevos, donde 82 de 107 (77%) eventos de predación correspondieron a huevos picados por tordos. Los nidos construidos en cardos tuvieron tasas de predación y parasitismo más altas que las correspondientes a nidos construidos en otros sustratos, probablemente debido a que los tordos exhiben una mayor actividad en el área donde los cardos son el único sustrato de nidificación disponible. La tasa de parasitismo mostró una tendencia a crecer con la distancia al nido más próximo, probablemente debido a la defensa parental y los despliegues de defensa comunales de Pseudoleistes virescens. La proporción de nidos descubiertos por tordos fue mayor para nidos activos (95%) que para nidos experimentales (29%), lo cual sugiere que los tordos utilizaron la actividad parental para detectar los nidos. A pesar de la activa defensa del nido, descubrimos que la actividad parental no afectó ni la tasa de predación ni el tiempo de supervivencia de los nidos. De esta forma, a pesar de que la defensa del nido en Pseudoleistes virescens aparenta estar basada en la defensa cooperativa grupal, tal comportamiento no redujo el impacto de los parásitos de cría o predadores de nidos. [source]

Observations of predation by corvids at a Marbled Murrelet nest

JOURNAL OF FIELD ORNITHOLOGY, Issue 2 2007
Percy N. Hébert
ABSTRACT Unlike other alcids, Marbled Murrelets (Brachyramphus marmoratus) typically nest solitarily on large platforms in the upper canopy of old-growth coniferous trees. Although Marbled Murrelets exhibit characteristics that minimize the risk of predation, habitat fragmentation has likely increased the risk of nest predation by corvids. Using a video camera at a nest in northern California, we observed nest fates for 4 yr (2002,2005). These recordings revealed two cases of egg predation by a Steller's Jay (Cyanocitta stelleri) and a Common Raven (Corvus corax), respectively. In both instances, the egg was carried from the nest site, leaving no evidence that nesting had occurred. Our observations revealed (1) the need to be conservative in estimates of nesting attempts and nesting success of Marbled Murrelets based only on the presence or absence of eggshell fragments or feces, (2) that not all predation attempts were successful, and (3) that murrelets may be more susceptible to predation early in the incubation period when adults may be less attentive to eggs and, after hatching, when young are less than 14 d old. We encourage efforts to minimize anthropogenic activities that may increase local corvid densities or disturb murrelets during the early incubation period. SINOPSIS Contrario a otros álcidos, la uria (Brachyramphus marmoratus), anida comunmente, de forma solitaria en grandes plataformas en el docel de bosques maduros de coníferos. Aunque estas aves exhiben características que minimizan el riesgo de depredación, la fragmentación de habitat ha incrementado el mismo, particularmente por parte de córvidos. Utilizando una cámara de video en un nido en el norte de California,observamos el fracaso de nidos por cuatro años (2002,2005). Las grabaciones revelaron dos casos de depredación de huevos por parte de Cyanocitta stelleri y Corvus corax, respectivamente. En ambos casos, los huevos fueron cargados, y no se dejo evidencia de depredación. Nuestras observaciones revelan: (1) la necesidad de ser conservador cuando hace estimados de intentos de anidamiento y éxito de anidamiento de urias basado en la presencia o ausencia de fragmentos de cascarones o heces fecales, (2) que no todos los intentos de depredación fueron exitosos, y (3) que el ave estudiada pudiera ser más suceptibles a la depredación temprano en el periodo de incubación, cuando los adultos pudieran darle menor atención a los huevos, y luego del eclosionamiento, cuando los pichones tienen menos de 14 días. Fomentamos los esfuerzos para minimizar actividades antropogénicas que puedan incrementar las densidades locales de córvidos o el disturbio de urias durante las etapas tempranas de incubación. [source]

Broods of attractive three-spined stickleback males require greater paternal care

JOURNAL OF FISH BIOLOGY, Issue 4 2006
T. C. M. Bakker
The relationship between egg number and survival in nests of three-spined sticklebacks Gasterosteus aculeatus was tested in the field. Nests were deprived of paternal care during a variable period by removal of the father while preventing egg predation by protection of the nest by a net. Upon male removal, a number of male traits were quantified. Nest-content variables and embryo survival were assessed at the end of the deprivation period. Proportional egg mortality was significantly positively correlated with the length of the deprivation period, the number of eggs present in the nest and egg size, thus suggesting that nests with more and larger eggs need more paternal care. Males with the most symmetrical ventral spines achieved the highest reproductive success as measured by the number of eggs in the nest. In addition, their nests contained relatively larger eggs. Spine length symmetry correlated with the blue intensity of the eye thus giving females several cues to assess male quality. [source]

Evaluating the enemies hypothesis in a clover-cabbage intercrop: effects of generalist and specialist natural enemies on the turnip root fly (Delia floralis)

AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2010
Maria Björkman
1The relative importance of the resource concentration hypothesis and the enemies hypothesis was investigated for the turnip root fly Delia floralis in a cabbage,red clover intercropping system compared with a cabbage monoculture. 2Delia floralis egg densities were measured as well as the activity-densities of generalist predators in a field experiment during two growing seasons. In the second year, a study of egg predation with artificially placed eggs was conducted, in addition to a predator exclusion experiment, to estimate total predation during the season. Parasitization rates were estimated from samples of pupae. 3Delia floralis oviposition was greater in the monoculture during both years. The predator activity-densities differed between treatments and study years. The known natural enemies of Delia spp., Bembidion spp. and Aleochara bipustulata showed a strong response to a cultivation system with higher activity-densities in the monoculture. The response, however, appeared to be caused primarily by habitat preferences and not by D. floralis egg densities. 4The reduction in the number of D. floralis pupae in the intercropping may be explained by a disruption in oviposition behaviour caused by the presence of clover because neither predation, nor parasitization rates differed between cultivation systems. [source]

Competition and intraguild egg predation among freshwater snails: re-examining the mechanism of interspecific interactions

OIKOS, Issue 11 2007
Andrew M. Turner
Experimental and field studies suggest that freshwater snail species have negative effects on each other's population growth rates. Because snails share similar diets, these interactions have been interpreted as the result of exploitative competition, but they could also result from intraguild predation. Here we present three experiments aimed at testing the hypothesis that interspecific interactions among three species of freshwater gastropod (Helisoma trivolvis, Physa acuta and Stagnicola elodes) are mediated by intraguild egg predation. Foraging trials, conducted in a laboratory, showed that some snails readily prey on eggs, but the extent of egg predation depended on both the identity of the snail predator and the identity of the egg mass. Of the three species considered, Stagnicola had the largest effect on egg mortality and Physa had no effect on egg mortality. Foraging trials also showed that the eggs of Physa were the most vulnerable to predators and that the eggs of Stagnicola were largely invulnerable. A study conducted in large outdoor mesocosms assessed the occurrence of egg mortality in an environment of more extensive spatial scale and complexity. The results largely mirrored those of the laboratory study, with Stagnicola being the most voracious predator and the eggs of Physa being most vulnerable to predation. The reproductive success of Physa and Stagnicola raised in sympatry and allopatry was assessed in a mesocosm study conducted over three months. Recruitment of both species was depressed in sympatry, but patterns of growth in the survivors suggest contrasting mechanisms of suppression: Physa suppressed Stagnicola via exploitative competition, but Stagnicola suppressed Physa via egg predation. These experiments support the hypothesis that freshwater snail assemblages are structured by strong interspecific interactions and that a rich interplay of egg predation and interspecific competition underlie interactions among the members of this guild. [source]