Predation of experimental nests is linked to local population dynamics in a fragmented bird population

Artificial nest experiments (ANEs) are widely used to obtain proxies of natural nest predation for testing a variety of hypotheses, from those dealing with variation in life-history strategies to those assessing the effects of habitat fragmentation on the persistence of bird populations. However, their applicability to real-world scenarios has been criticized owing to the many potential biases in comparing predation rates of artificial and natural nests. Here, we aimed to test the validity of estimates of ANEs using a novel approach. We related predation rates on artificial nests to population viability analyses in a songbird metapopulation as a way of predicting the real impact of predation events on the local populations studied. Predation intensity on artificial nests was negatively related to the species' annual population growth rate in small local populations, whereas the viability of large local populations did not seem to be influenced, even by high nest predation rates. The potential of extrapolation from ANEs to real-world scenarios is discussed, as these results suggest that artificial nest predation estimates may predict demographic processes in small structured populations.     

Predation on artificial,solitary and aggregated wader nests on farmland

Predation rates on artificial wader nests, solitary curlew (Numenius arquata) and lapwing (Vanellus vanellus) nests and lapwing nests in colonies were studied on a farmland site in central Sweden. Predation rates were highest on artificial wader nests, intermediate on solitary curlew and lapwing nests and lowest on lapwing nests in colonies, probably because of active defence of adults at real nests and/or because of selection of nest sites with lower predation risk by breeding birds. A comparison of nests close to (50 m) and far away from (200 m) forest edges revealed no increased predation risk close to edges for any of the studied nest types. Predation risk changed during the season for artificial nests (highest in the middle of May), while predation rates on lapwing and curlew nests were more stable. Artificial nests seem to be inappropriate for measuring actual predation rates and temporal differences in predation rates on real nests, but they might be suitable for use as an index of spatial differences.     

Predation on artificial bird nests in chaparral fragments

Summary The predation rate of artificial bird nests was measured in disturbed chaparral habitat fragments and at an unfragmented site in coastal San Diego County, California USA. Local extinctions of chaparral birds has been previously shown to occur in these fragments. The predation rate was highest at the unfragmented site. Among fragments, predation was higher at moderately disturbed than at highly disturbed sites. These results suggest that nest predator species diversity or density is reduced in disturbed chaparral fragments. Nest predation is probably not the most important cause of the observed loss of chaparral breeding bird diversity in these fragments.     

Predators of Spotted Flycatcher Muscicapa striata nests in southern England as determined by digital nest-cameras

Capsule Avian predators are principally responsible.

Aims To document the fate of Spotted Flycatcher nests and to identify the species responsible for nest predation.

Methods During 2005–06, purpose-built, remote, digital nest-cameras were deployed at 65 out of 141 Spotted Flycatcher nests monitored in two study areas, one in south Devon and the second on the border of Bedfordshire and Cambridgeshire.

Results Of the 141 nests monitored, 90 were successful (non-camera nests, 49 out of 76 successful, camera nests, 41 out of 65). Fate was determined for 63 of the 65 nests monitored by camera, with 20 predation events documented, all of which occurred during daylight hours. Avian predators carried out 17 of the 20 predations, with the principal nest predator identified as Eurasian Jay Garrulus glandarius. The only mammal recorded predating nests was the Domestic Cat Felis catus, the study therefore providing no evidence that Grey Squirrels Sciurus carolinensis are an important predator of Spotted Flycatcher nests. There was no evidence of differences in nest survival rates at nests with and without cameras. Nest remains following predation events gave little clue as to the identity of the predator species responsible.

Conclusions Nest-cameras can be useful tools in the identification of nest predators, and may be deployed with no subsequent effect on nest survival. The majority of predation of Spotted Flycatcher nests in this study was by avian predators, principally the Jay. There was little evidence of predation by mammalian predators. Identification of specific nest predators enhances studies of breeding productivity and predation risk.     

Nest position and type affect predation rates of artificial avian nests in the tropical lowland forest on Mount Cameroon

Nest predation is the leading cause of reproductive failure in birds and thus it shapes their life history strategies. Intensities of nest predation appear to differ among nest locations and types in both temperate and tropical regions. However, there is limited knowledge of factors influencing susceptibility of avian nests to predation in Africa. The aim of our study was to investigate artificial nest predation rates of different ground and shrub nests located at different heights in the rainforest undergrowth. We placed artificial avian nests within a homogeneous lowland forest interior with sparse forest undergrowth in the Mount Cameroon National Park, Cameroon. We exposed three sets of nests: 50 bare-ground, 50 cup-ground and 50 cup-shrub nests, for 10 d. Predation was higher for cup-ground nests compared to cup-shrub nests, and bare-ground nests were more depredated than cup-ground nests. We concluded that the presence of a cup as well as higher nest position significantly increased probability of artificial nest survival. The results of this study suggest a potential selection pressure on nest type and placement in lowland forest birds for a poorly known tropical region.     

Predation of Lapwing Vanellus vanellus nests on lowland wet grassland in England and Wales: effects of nest density, habitat and predator abundance

There is concern that predation of Lapwing Vanellus vanellus nests may create additional pressure on declining populations of this species in Europe. At seven sites in England and Wales, daily nest predation rates on 1,390 nests were related to variables using Generalised Linear Mixed Models. The strongest predictor was Lapwing nest density (number of nests within 100 m): predation rates declined as nest density increased. Since nocturnal species, probably mammals, have been identified as the major predators of Lapwing nests at these sites, these results suggest that Lapwings are able to deter mammalian predators or may settle to nest at high densities in areas with low predation pressure. At the site level, there was no relationship between Lapwing nesting density and fox density, and a positive relationship with Carrion Crow Corvus corone nesting density. There was a weaker effect of distance to field boundary: nests closer to boundaries were more likely to be predated. Weak interactive effects between crow density and both nest visibility and distance to vantage point were identified in models using a reduced subset of nests. These were counter-intuitive, did not persist in the larger data set, and do not have obvious explanations. If Lapwings nesting at high density are able to deter predators, there are implications for land management. Smaller areas could be managed within potential breeding habitat to encourage Lapwings to nest in dense colonies. Selection of larger fields for such management, where nests could be located far from the field boundary should improve the value of such measures.     

Predation by jaguar on howler monkeys (Alouatta seniculus) in Venezuela

We document the loss of all but the youngest member of a troop of six howler monkeys due to probable jaguar predation during a 7-month period in 1988. The formation of Guri Lake resulted in forest fragmentation which forced monkeys into new and unfamiliar areas and altered the balance of predator and prey populations, and may thus have contributed indirectly to the success of the jaguar. The selection of defoliated (dead) trees for sleeping sites by the howlers may have directly increased the risk of predation. © 1992 Wiley-Liss, Inc.     

Predicting species interactions from edge responses: mongoose predation on hawksbill sea turtle nests in fragmented beach habitat

Because species respond differently to habitat boundaries and spatial overlap affects encounter rates, edge responses should be strong determinants of spatial patterns of species interactions. In the Caribbean, mongooses (Herpestes javanicus) prey on hawksbill sea turtle (Eretmochelys imbricata) eggs. Turtles nest in both open sand and vegetation patches, with a peak in nest abundance near the boundary between the two microhabitats; mongooses rarely leave vegetation. Using both artificial nests and hawksbill nesting data, we examined how the edge responses of these species predict the spatial patterns of nest mortality. Predation risk was strongly related to mongoose abundance but was not affected by nest density or habitat type. The product of predator and prey edge response functions accurately described the observed pattern of total prey mortality. Hawksbill preference for vegetation edge becomes an ecological trap in the presence of mongooses. This is the first study to predict patterns of predation directly from continuous edge response functions of interacting species, establishing a link between models of edge response and species interactions.     

Predation on Colorado Potato Beetle Eggs by Generalist Predators in Research and Commercial Potato Plantings

Field studies quantified predation on Colorado potato beetle [Leptinotarsa decemlineata(Say)] eggs and determined the relationship between predation and egg mass abundance in research and commercial potato plantings in eastern North Carolina. Predator exclusion experiments were conducted weekly in research plantings. In addition, egg mass density and predation on egg masses were monitored throughout the season in research plots and commercial potato fields. Predation was an important source of mortality for Colorado potato beetle eggs. Survivorship of eggs exposed to predators was consistently, significantly lower than survivorship of eggs protected from predation. Averaged over 2 years, the mean survivorship of eggs protected from predation was 69%, compared with 26% survivorship of eggs exposed to predation. Regression analysis failed to detect any relationship between egg mortality due to predation and egg abundance. These results imply that efforts to reduce Colorado potato beetle populations selectively will not be offset by an according decline in abundance of natural enemies and therefore should be fully compatible with naturally occurring biological control.     

千岛湖栖息地片段化效应对鸟类巢捕食风险的影响

为了解栖息地片段化对鸟类巢捕食风险的影响,我们于2010年4-8月,在千岛湖地区选取16个岛屿,分别在岛屿边缘和内部区域用放置鸡蛋(大型卵)和鹌鹑(Coturnix japonica)蛋(小型卵)的方法进行人工模拟地面巢试验,研究不同体积大小鸟卵的巢捕食率及其差异,分析巢捕食率与岛屿面积、隔离度、形状指数和植物物种丰富...     

Kinetic analysis of the effect of cell density on hybridoma cell growth in batch culture

The effect of cell density on cell growth was investigated in a suspension batch culture of hybridoma cells. The specific growth rate was found to increase with increasing initial cell density and then to decrease with further increases in initial cell density. In order to quantitatively describe the dependence of specific growth rate on cell density, a kinetic model is proposed, which satisfactorily represents the experimental data.     

The population ecology of Rattus exulans on Tiritiri Matangi Island,and a model of comparative population dynamics in New Zealand

Abstract

On Tiritiri, a small predator-free island in northern New Zealand, kiore (Rattus exulans) were live and snap trapped in grassland and forest. In both habitats, kiore abundance peaked in late summer/autumn. The increase followed a 3 month breeding season during which females produced two to three litters, each averaging 7 young. During the population decline in autumn and winter, animals lost weight. Few bred in the breeding season of their birth and none lived to breed in a second breeding season, so the population consisted of distinct age cohorts. These patterns may relate to a highly seasonal food supply.

Kiore elsewhere in New Zealand show seasonal breeding, but the length of breeding, sexual maturation, and litter size vary. Other studies of kiore in the Pacific show less marked seasonal fluctuations, longer breeding seasons, and smaller litters. We propose a model to explain the variation in rodent demography in New Zealand. The model is based on the seasonal availability of food, along with the modifying influences of predation and dispersal.     

Role of prey and intraspecific density dependence on the population growth of an avian top predator

Exploring predator–prey systems in diverse ecosystems increases our knowledge about ecological processes. Predator population growth may be positive when conspecific density is low but predators also need areas with prey availability, associated with competition, which increases the risk of suffering losses but stabilises populations. We studied relationships between European rabbits Oryctolagus cuniculus (prey) and adult eagle owls Bubo bubo (predators) in south-western Europe. We assessed models explaining the predator population growth and stability. We estimated the abundance of rabbits and adult eagle owls during three years in eight localities of central-southern Spain. We explored models including rabbit and adult eagle owl abundance, accounting for yearly variations and including the locality as a random variable. We found that population growth of adult eagle owls was positive in situations with low conspecific abundance and tended to be negative but approaching equilibrium in situations of higher conspecific abundance. Population growth was also positively related to previous summer rabbit density when taking into account eagle owl conspecific abundance, possibly indicating that rabbits may support recruitment. Furthermore, abundance stability of adult eagle owls was positively related to previous winter–spring rabbit density, which could suggest predator population stabilisation through quick territory occupation in high-quality areas. These results exemplify the trade-off between prey availability and abundance of adult predators related to population growth and abundance stability in the eagle owl–rabbit system in south-western Europe. Despite rabbits have greatly declined during the last decades and eagle owls locally specialise on them, eagle owls currently have a favourable conservation status. As eagle owls are the only nocturnal raptor with such dependence on rabbits, this could point out that predators may overcome prey decreases in areas with favourable climate and prey in the absence of superior competitors with similar foraging mode.     

Differential effects of elevated CO2 on acorn density, weight, germination, and predation among three oak species in a scrub-oak forest

Much research on the effects of elevated CO₂ on forest trees has focused on quantitative changes in photosynthesis, secondary chemistry, and plant biomass. However, plant fitness responses to rising CO₂ should also include quantitative measures of reproduction, since most forest systems are recruitment limited. Until now, it has proved very difficult to grow forest trees to sexual maturity in a CO₂‐enriched environment. This paper is the first of its kind to address the effects of elevated CO₂ on the reproduction of hardwood trees in a natural forest. Beginning in 1996, scrub‐oak vegetation, predominantly three species of scrub‐oaks, Quercus myrtifolia, Q. chapmanii, and Q. geminata, were grown inside eight chambers with elevated CO₂ (704 parts per million (ppm)) and eight with ambient CO₂ (379 ppm) at Kennedy Space Center, Florida. In elevated CO₂, acorn production increased significantly for the dominant species Q. myrtifolia and for Q. chapmanii, but it did not increase for the subdominant, Q. geminata. Acorn weight, germination rate, and predation by weevils were unaffected by CO₂. Thus, recruitment of some forest tree species into the Florida scrub‐oak community is likely to be accelerated in an atmosphere of increased CO₂. However, because the acceleration of recruitment differs among species, over the long term, Q. myrtifolia and Q. chapmanii will be favored over Q. geminata and this is likely to change patterns of species diversity.