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Juvenile Recruitment (juvenile + recruitment)

Distribution by Scientific Domains

Life Sciences	66%
Earth and Environmental Science	33%

Selected Abstracts

Interannual changes in sablefish (Anoplopoma fimbria) recruitment in relation to oceanographic conditions within the California Current System

FISHERIES OCEANOGRAPHY, Issue 1 2006
MICHAEL J. SCHIRRIPA
Abstract Sablefish (Anoplopoma fimbria) supports substantial fisheries in both the eastern and western Pacific Oceans. Juvenile recruitment along the west coast of the continental United States has been highly variable over the past three decades. Using a generalized additive model, we demonstrate that physical oceanographic variables within the California Current System have significant effects on sablefish recruitment. Significant relationships were found between juvenile recruitment and northward Ekman transport, eastward Ekman transport, and sea level during key times and at key locations within the habitat of this species. The model explains nearly 70% of the variability in sablefish recruitment between the years 1974 and 2000. The predictive power of the model was demonstrated by refitting without the last 5 yr of data and subsequent prediction of those years. Bootstrap assessments of bias associated with parameter estimates and jackknife-after-bootstrap assessments of the influence of individual data on parameter estimates are presented and discussed. Using this model, it is possible to draw preliminary conclusions concerning year-class strength of cohorts not yet available to the survey gear as well as historic year-class strengths. We discuss changes in zooplankton abundance and shifts in species of copepods associated with fluctuations in the physical variables that appear to have a major influence on sablefish recruitment. [source]

Demographic Characteristics of Lytechinus variegatus (Echinoidea: Echinodermata) from Three Habitats in a North Florida Bay, Gulf of Mexico

MARINE ECOLOGY, Issue 1 2000
Steven D. Beddingfield
Abstract. The population densities, spatial distributions, size frequencies, growth rates, longevity and reproductive activities of sub-populations of the sea urchin Lytechinus variegatus were investigated over a two-year period. Sea urchins were examined in three habitats in Saint Joseph Bay, Florida, which is within the northern limits of their distribution. Densities of sea urchins, which ranged as high as 35 individuals ·,2, fluctuated seasonally at all sites and were higher in seagrass beds comprised of Thalassia testudinum than Syringodium filiforme or on a sand flat. A cold front caused large-scale, catastrophic mortality among adult, and especially juvenile, sea urchins in nearshore habitats of the Bay in the spring of 1993, leading to a dramatic decline in sea urchin densities at the Thalassia seagrass site. The population recovered over 6 months at this site and was attributable to immigration of new adults. Juvenile recruitment displayed both interannual and site-specific variability, with recruitment being highest in seagrass habitats in fall and spring. The most pronounced recruitment event occurred in fall 1993 at the Thalassia site. Spatial distributions of adult individuals ascertained monthly never varied from random in the seagrass beds (T. testudinum and S. filiforme) or during spring, summer or fall months on the sand flat. Nonetheless, aggregations of adult sea urchins were observed on the sand flat in the winter months and were associated with patchy distributions of plant food resources. Juvenile sea urchins (< 25 mm test diameter) exhibited aggregations at all sites and 67 % of all juveniles under 10 mm test diameter (91 of 165 individuals observed) were found under the spine canopies of adults. Measurements of the inducibility of spawning indicated peak gametic maturity in all three sub-populations in spring and summer. Gonad indices varied between habitats and years, but distinct maxima were detected, particularly in spring 1993 and late summer 1994. The mean gonad index of individuals at the Syringodium seagrass site was 2- to 4-fold higher than the other sites in spring 1993 and gonad indices were much higher at all sites in spring of 1993 than 1994. Estimates of growth based on changes in size frequency cohorts coupled with measurements of growth bands on lantern demipyramids indicated that L. variegatus in three habitats of Saint Joseph Bay have similar growth rates and attain a mean test diameter of approximately 35 mm in one year. In contrast to populations within the central biogeographical range of the species, which may attain test diameters up to 90 mm, the largest individuals recorded in Saint Joseph Bay were 60 mm in test diameter, and almost all individuals were no more than 45 mm in test diameter or two years of age. The demographics of L. variegatus in the northern limits of their distribution appear to be strongly influenced by latitudinally driven, low-temperature events and secondarily by local abiotic factors, especially springtime low salinities, which may negatively impact larval development and recruitment. [source]

Seed Dispersal of the Palm Syagrus romanzoffiana by Tapirs in the Semi-deciduous Atlantic Forest of Argentina

BIOTROPICA, Issue 4 2009
Mariano I. Giombini
ABSTRACT Vertebrates play a fundamental role in the dispersal of Neotropical trees, generating different seed shadows according to their physical and behavioral features. Tapirs are capable of consuming great quantities of large fruits, and they defecate seeds far from parent trees. For instance, intact seeds of the palm Syagrus romanzoffiana have been found in tapir dung piles in the Atlantic Forest of southeastern Brazil, suggesting that tapirs effectively disperse this species. However, recruitment was not examined therein. We studied tapir endozoochory of large and medium seeds in the semi-deciduous Atlantic Forest of Argentina by examining dung piles found within Iguazu National Park. We recorded dung-pile positions to evaluate the spatial distribution. We also counted the number of juveniles in 2 × 2 m quadrats placed on old dung piles in latrines, beneath adults and in random sites to estimate recruitment levels. Syagrus romanzoffiana seeds were present in 98 percent of dung piles, averaging >200 seeds/dung pile, indicating that this species constitutes the main fruit component in the tapir's diet. Dung piles showed a clumped deposition pattern reflecting the use of latrines. Juvenile recruitment in latrines was 21 times higher than that of under-adult sites and 500 times greater than in random sites, and correlated with the frequency of use of the areas. We concluded that the lowland tapir is a major disperser of S. romanzoffiana. Given that this palm can be considered a keystone species, a disruption of this interaction might affect the entire community of frugivores in the long term. [source]

Responses of Tuatara (Sphenodon punctatus) to Removal of Introduced Pacific Rats from Islands

CONSERVATION BIOLOGY, Issue 4 2007
DAVID R. TOWNS
erradicación de rata del Pacífico; especie invasora; índice de condición corporal; tuatara Abstract:,Invasive mammalian predators such as rats are now widespread on islands, but hypotheses about their effects have rarely been tested. Circumstantial evidence from New Zealand indicates that, when introduced to islands, Pacific rats (Rattus exulans) have negative effects on endemic plants, invertebrates, birds, and reptiles, including the tuatara (Sphenodon punctatus). We tested the effects of Pacific rats on tuatara by comparing the demographic structure and body condition of tuatara populations on three islands before and after removal of rats and on a fourth island where rats remained. In the presence of rats, juvenile tuatara constituted on average 0,5% of the sample tuatara populations. When Pacific rats were removed after at least 200 years' occupancy, the proportion of juvenile tuatara increased 3.5- to 17-fold and body condition of adult males and females also improved (sometimes dramatically). We predict that, unless Pacific rats are removed from Taranga Island, the tuatara population will collapse because of low population density and the lack of juvenile recruitment. Our results demonstrate that when invasive species exert subtle effects on recruitment and body condition, the effects on populations of long-lived endemic species may only become apparent long after the invasion. Resumen:,Actualmente, los depredadores mamíferos invasores, como las ratas, están ampliamente extendidos en islas, pero las hipótesis sobre sus efectos han sido probadas pocas veces. Evidencia circunstancial de Nueva Zelanda indica que, cuando son introducidas a islas, las ratas del Pacífico (Rattus exulans) tienen un efecto negativo sobre plantas, invertebrados, aves y reptiles endémicos, incluyendo el tuatara (Sphenodon punctatus). Probamos los efectos de ratas del Pacífico sobre tuatara mediante la comparación de la estructura demográfica y la condición corporal de poblaciones de tuatara en tres islas antes y después de la remoción de ratas y en una cuarta isla donde permanecían las ratas. En la presencia de ratas, tuatara juveniles constituían, en promedio, 0,5% de las poblaciones de tuatara. Cuando las ratas eran removidas después de por lo menos 200 años de ocupación, la proporción de tuatara juveniles incremento entre 3.5 y 17 veces y la condición corporal de los machos y hembras adultas también mejoró (algunas veces dramáticamente). Pronosticamos que, a menos que las ratas del Pacífico sean removidas de la Isla Taranga, las poblaciones de tuatara se colapsarán debido a una densidad poblacional baja y por la ausencia de reclutamiento de juveniles. Nuestros resultados demuestran que cuando las especies invasoras ejercen efectos sutiles sobre el reclutamiento y la condición corporal, los efectos sobre las poblaciones de especies endémicas longevas se vuelven aparentes mucho tiempo después de la invasión. [source]

Variation in Pesticide Tolerance of Tadpoles among and within Species of Ranidae and Patterns of Amphibian Decline

CONSERVATION BIOLOGY, Issue 5 2000
Christine M. Bridges
Because variability exists among organisms in their sensitivity to environmental stressors, it is important to determine the degree of this variation when undertaking conservation efforts. We conducted both lethal (time-to-death) and sublethal (activity change) assays to determine the degree of variation in the sensitivity of tadpoles to a pesticide, carbaryl, at three hierarchical levels: among ranid species, among several populations of a single ranid species ( Rana sphenocephala), and within populations of R. sphenocephala. We observed significant variation in time to death among the nine ranid species and among the 10 R. sphenocephala populations we tested. Four out of eight R. sphenocephala populations exhibited significantly different times to death among families. The magnitude of the activity change in response to exposure to sublethal carbaryl levels was significantly different among species and within R. sphenocephala populations. Chemical contamination, at lethal or sublethal levels, can alter natural regulatory processes such as juvenile recruitment in amphibian populations and should be considered a contributing cause of declines in amphibian populations. Resumen: Existe una variación significativa entre y dentro de especies de anfibios con respecto a los reportes de disminuciones poblacionales; las especies en disminución son frecuentemente encontradas en ambientes que son fisiográficamente similares a ambientes donde las mismas especies están prosperando. Debido a que la variabilidad existe entre organismos en lo referente a su sensibilidad a estresores ambientales, es importante determinar el grado de esta variación cuando se lleven a cabo esfuerzos de conservación. Nosotros llevamos a cabo ensayos tanto letales (tiempo de muerte) como subletales (cambios de actividad) para determinar el grado de variación en la sensibilidad de renacuajos a un pesticida, carbaryl, en tres niveles jerárquicos: entre especies de ránidos, entre diversas poblaciones de una sola especie de ránido ( Rana sphenocephala) y dentro de poblaciones de R. sphenocephala. Observamos diferencias significativas en tiempo de muerte entre las nueve especies de ránidos y entre las 10 poblaciones de R. sphenocephala evaluadas. Cuatro de ocho poblaciones de R. sphenocephala exhibieron tiempos de muerte significativamente diferentes entre familias. La magnitud del cambio de actividad al ser expuestas a niveles subletales de carbaryl fue significativamente diferente entre especies y dentro de poblaciones de R. sphenocephala. La contaminación química, a niveles letales y subletales, puede alterar los procesos reguladores naturales (por ejemplo el reclutamiento de juveniles) en poblaciones de anfibios y debería ser considerado como una causa que contribuye a la disminución de poblaciones de anfibios. [source]

Postflood movements and population connectivity in gambusia (Gambusia holbrooki)

ECOLOGY OF FRESHWATER FISH, Issue 4 2006
P. Chapman
Abstract , A population of the exotic pest fish Gambusia holbrooki inhabiting a drainage channel was sampled regularly to record responses to flooding and subsequent population reestablishment. The flood reduced numbers in the channel to near-zero levels. After remaining very low for 2 months, densities increased steadily through juvenile recruitment and the concentration of fish in drying pools. Tagging revealed that in general, movements between pools separated by only a few metres were relatively limited. There was evidence for habitat segregation and population subdivision, as fish from different pools varied markedly in terms of mean population density, movement behaviour, sex and size composition and juvenile recruitment. The most favoured pool was relatively deep, well lit and had the greatest habitat diversity. Gambusia control measures are likely to be most effective if timed to coincide with floods (which reduce local population densities) and/or droughts (which concentrate fish and allow targeting of source populations). [source]

Diplodus spp. assemblages on artificial reefs: importance for near shore fisheries

FISHERIES MANAGEMENT & ECOLOGY, Issue 2 2009
F. LEITÃO
Abstract, Artificial reefs have been deployed along the southern coast of Portugal (Algarve) since 1990 to enhance artisanal fisheries. The objectives of this study were to: (1) describe the colonisation process; (2) assess the role of the artificial reefs in terms of juvenile recruitment and growth and as mating/spawning areas and (3) evaluate the potential of artificial reefs as near shore artisanal fishing grounds for three economically important fish species, Diplodus bellottii (Steindachner), Diplodus sargus (L.) and Diplodus vulgaris (Geoffroy Saint-Hilaire). The fish assemblages were monitored after the deployment of a large artificial reef (Faro/Ancão) in 2002. Colonisation rates for the three species were fast. Artificial reefs play a multiple role for Diplodus spp., acting as recruitment, growth and nursery areas for juveniles, and spawning/mating areas for adults, and can thus be considered essential fish habitat. Three months after deployment of the artificial reefs, exploitable biomass was 16, 29 and 8 kg per reef group, respectively, for D. bellotti, D. sargus and D. vulgaris. These results indicate that artificial reefs quickly become good fishing grounds, where suitable financial yields may be obtained by fisher. Moreover, the artificial reefs became new and alternative fishing grounds, allowing reduction of fishing effort over traditional rocky areas that are scarce along the Algarve coast. Management measures for artificial reefs, in terms of fishing strategies, are discussed. [source]

Interannual changes in sablefish (Anoplopoma fimbria) recruitment in relation to oceanographic conditions within the California Current System

Invasion by Rattus rattus into native coastal forests of south-eastern Australia: are native small mammals at risk?

AUSTRAL ECOLOGY, Issue 4 2009
VICKI L. STOKES
Abstract The black rat, Rattus rattus, is an alien rodent in Australian ecosystems where niche overlap with native small mammals may lead to competition for resources and displacement of native species. In coastal habitats surrounding Jervis Bay in south-eastern Australia, R. rattus co-occurs with the native bush rat, Rattus fuscipes, and brown antechinus, Antechinus stuartii. Relative distributions and abundances, and fine-scale space use suggest invasive and native rodents compete for use of space and habitat. Such competitive interactions were not evident between R. rattus and native A. stuartii, which was negatively influenced more by disturbance to habitat. Differences in rodent communities between spatially separate forests forming the northern and southern peninsulas of Jervis Bay potentially reflect symmetrical competition and differences in competitive outcomes. In southern forests, R. rattus was largely restricted to patches of disturbed forest associated with campgrounds. Competitive interference by native rodent populations inhabiting surrounding intact forests may have so far limited R. rattus colonization of these areas. In northern forests, R. rattus was the predominant rodent irrespective of disturbance, while populations of R. fuscipes were unusually low seemingly due to poor juvenile recruitment. Native individuals avoided areas frequented by adult R. rattus and given that species did not partition use of microhabitats, R. rattus most likely precluded R. fuscipes from suitable habitat and in doing so limited native populations. We discuss how natural disturbance of habitat and human activity have potentially facilitated successful invasion by R. rattus of the northern forests. Studies that manipulate rodent populations are required to support these interpretations of observed patterns. [source]