As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free-living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual-based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro-invertebrates. Intake rate is measured as the ash-free dry mass (AFDM) per second of active foraging ; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type II (' disc equation ') formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching.A review of 30 functional responses showed that intake rate in free-living shorebirds varied independently of prey density over a wide range, with the asymptote being reached at very low prey densities (<150/m x2 ). Accordingly, most of the many studies of shorebird intake rate have probably been conducted at or near the asymptote of the functional response, suggesting that equations that predict intake rate should also predict the asymptote.A multivariate analysis of 468 ' spot ' estimates of intake rates from 26 shorebirds identified ten variables, representing prey and shorebird characteristics, that accounted for 81% of the variance in logarithm-transformed intake rate. But four-variables accounted for almost as much (77.3%), these being bird size, prey size, whether the bird was an oystercatcher Haematopus ostralegus eating mussels Mytilus edulis, or breeding. The four variable equation under-predicted, on average, the observed 30 estimates of the asymptote by 11.6 %, but this discrepancy was reduced to 0.2% when two suspect estimates from one early study in the 1960s were removed. The equation therefore predicted the observed asymptote very successfully in 93% of cases.We conclude that the asymptote can be reliably predicted from just four easily measured variables. Indeed, if the birds are not breeding and are not oystercatchers eating mussels, reliable predictions can be obtained using just two variables, bird and prey sizes. A multivariate analysis of 23 estimates of the half-asymptote constant suggested they were smaller when prey were small but greater when the birds were large, especially in oystercatchers. The resulting equation could be used to predict the half-asymptote constant, but its predictive power has yet to be tested.As well as predicting the asymptote of the functional response, the equations will enable research workers engaged in many areas of shore...
Patch dynamics of intertidal Pyura praeputialis (Heller, 1878) were studied in experimentally cleared plots at 3 vertical levels (upper, mid and lower P. praeputialis levels) and 3 sites within the Bay of Antofagasta, Chile. The sites corresponded approximately to the northern limit (Las Conchillas), the center (El Way), and the southern limit (El Lenguado) of the species geographic distribution in Chile. Replicated 40 × 60 cm quadrats were photographed periodically to follow patch re-colonization. Patch recolonization (recolonized area) followed a sigmoid curve and could be fitted at most sites and levels by applying maximum likelihood techniques to the asymptotic model:where Parameters a and b are asymptotic percentage cover and time for 50% recovery respectively, and Parameter c defines the shape of the curve (growing phase). Among sites, the highest asymptotic values and fastest recovery times were observed at El Way, in the center of the species distribution. Among levels, the highest asymptotic values were observed in the mid P. praeputialis level quadrats. The perimeter of the patches increased and subsequently decreased as a function of recolonized area. Recruitment observations showed the process of recolonization to be related to the perimeter of the patch to be colonized rather than to the area available. Further more, the recolonization patterns could be predicted using the patch perimeter scaled by a linear coefficient. We believe that the mechanism of recolonization is most probably related to the settlement of recruits to the border of previously settled individuals, possibly mediated by intraspecific self-facilitation mechanisms.
Abstract. The present study analyzes the distribution, population structure, population biomass and morphological characteristics of the intertidal tunicate Pyura stolonifera (Heller, 1878) in the Bay of Antofagasta, Chile, where the species shows a reduced geographical range extending around 60 – 70 km. Three sites along its distribution were studied. At the central site the tunicate presents the widest intertidal belts, reaching nearly 11 m (the mid‐intertidal‐Pyura‐zone shows the higher percent cover). Population dry biomass here averaged up to 20.45 kg·m–2, representing one of the highest intertidal specific biomasses reported in the literature. Lower values occur towards the borders of its distribution. Population densities were over 1800 indiv.·m–2 at mid‐intertidal‐Pyura‐belts. Crowding and competition potentially affect morphological characteristics and the energy/tissue allocation along the intertidal and geographical gradient of P. stolonifera.
Johngarthia planata (Stimpson, 1860) is an abundant and ecologically important land crab, distributed on East Pacific islands from the Gulf of California to Colombia. However, despite possible dispersal of planktotropMc larvae by sea currents, J. planata is not known from inshore islands and mainland of Central America. In this study, the presence of J. planata on Costa Rican inshore islands is reported for the first time, strongly supporting the significance of coastal currents for the distributional patterns of such species. Despite the proximity of the Costa Rican inshore islands to the mainland coast and larval dispersal by passing coastal currents, /. planata was not found in mainland locations. We suggest that a high diversity of continental land crab predators excludes /. planata from the continental mainland habitat, while the closely related Gecarcinus quadratus may have adaptations to high prédation pressure. RESUMENJohngarthia planata (Stimpson, 1860) es un cangrejo terrestre abundante y ecológicamente importante, que se encuentra en islas del Pacífico Oriental desde el Golfo de California a Colombia. Sin embargo, a pesar de la capacidad de dispersión de las larvas planctotróficas de J. planata no se conoce de islas cercanas a la costa o de la costa de América Central. En este estudio, se informa, por primera vez, de la presencia de J. planata en Costa Rica en islas cercanas a la costa, apoyando la importancia de corrientes costeras en los patrones de distribución de la especie. Aún así, J. planata no se encontró en el continente, a pesar de la cercanía de las islas costeras y su posibilidad de dispersión por corrientes. Sugerimos que la alta diversidad de cangrejos terrestres depredadores en el continente excluyen J. planata de habitats allí, mientras que Gecarcinus quadratus, una especie relacionada, puede estar adaptada a altas presiones de depredación. ' ) Present address: Bolivian Collection of Fauna,
Oystercatcher foraging behavior has been described for diverse intertidal prey such as limpets, mussels, and oysters. This paper describes foraging behavior of the American oystercatcher, Haematopous palliatus pitanay, on attached and wave-dislodged ascidians, Pyura praeputialis (prey with a restricted geographic range of 70 km) in the Bay of Antofagasta, Chile. Stabbed holes on the top of the ascidian's tunic, probing excursions, handling time, and five prey-handling sequential stages (striking, hammering, prying, cavity food searching, and swallowing) are described and measured. The need to determine ascidian profitability for oystercatcher species in Australia and Chile is highlighted.
Kott 1997). En la literatura se discute sobre las diferencias morfológicas del pico (largo y ancho) entre ambos tipos de ostreros. Dichas diferencias podrían segregar los roles de forrajeo de estas aves cuando comparten un mismo hábitat: los ostreros blancos atacarían preferentemente a presas de textura "blanda" y los ostreros negros atacarían presas de textura "dura" (i.e. cobertura calcárea). En este trabajo se consideró a P. praeputialis (piure de Antofagasta) como una presa de textura "blanda", ya que su tunica, compuesta por tunicina, es suave y flexible. En el estudio se comparan diversos aspectos ecológicos entre ambas especies de ostrero tales como: (a) abundancia de ostreros y de otras aves costeras que depredan sobre P. praeputialis, (b) distribución espacial de los ostreros en el manto de piure durante sus actividades de depredación, (c) tallas de piures preferidos, (d) tiempos de manipulación, (e) tasa de consumo y (f) frecuencia de consumo de otros invertebrados distintos del piure. Los resultados señalan a H. palliatus pitanay como la especie de ostrero que ataca con mayor frecuencia a P. praeputialis. Por otra parte, H. ater ataca con mayor frecuencia presas de textura "dura" como: lapas, caracoles, choritos, erizos]]>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.