Abundance and abundance change in the world's parrots

Estimates of population density and abundance change (differences in density or encounter rates across land uses or time periods) form the cornerstone of much of our knowledge of species' responses to environmental conditions, extinction risks and potential conservation actions. Gathering baseline data on abundance of the world's c. 10 000 bird species and monitoring trends in the light of rapidly changing environmental and harvest pressures is a daunting prospect. With this in mind, we review literature on population densities and abundance changes across habitats in one of the world's largest and most threatened bird families, the parrots (Psittaciformes), to identify gaps in knowledge, model phylogenetic and other influences on abundance, and seek patterns that might guide thinking for data‐deficient taxa and situations. Density estimates were found for only 25% of 356 parrot species. Abundance change data were similarly limited and most came from logged forest, with very few comparisons across different anthropogenic habitats. Threatened species were no more likely to have a density estimate than non‐threatened species, and were less likely to have estimates of abundance change. Exploratory generalized linear mixed models indicated that densities are most influenced by genus, and are generally higher within protected areas than outside. It is unclear whether the latter effect stems from habitat protection, a reduction in poaching or both, but protected areas appear to be beneficial for parrots. Individual members of the ‘parakeet’ genera (e.g. Pyrrhura and Eos) were predictably abundant, whereas within larger‐bodied genera such as Ara (macaws), species were predictably uncommon (< 10 individuals per km²) and there was a long tail of extreme rarity. Responses of parrots to habitat change were highly variable, with natural variation in parrot abundance across different primary forests as great as that between primary forest and human‐altered forests. The speed at which environmental change is affecting the world's parrots far outstrips that of our current capacity to track their abundance and we assess the likely scale of data deficiency in this and other bird groups. Developments in survey and analysis methods such as variants of distance sampling and the integration of niche modelling with point density estimation may increase our effectiveness in monitoring parrots and other important and threatened bird groups.     

Factors influencing the relative abundance of invasive predators and omnivores on islands

Invasive alien species (IAS) are the major cause of native species extinctions on islands worldwide. To mitigate or eliminate IAS impacts, eradication is often the best alternative. However, IAS removal may result in cascading effects, through increase in prey abundance, mesopredator release, or competitor release. Our objective is to determine which ecological processes may influence the relative abundance of invasive carnivores and rodents on an insular system. We find that feral cat and mustelids relative abundance was strongly related by prey abundance, and for the feral cat, abundance was also controlled by habitat; these results suggest that bottom-up control through environmental filtering could be the mechanism explaining predator abundance. For rodents, we find that the abundance of the black rat was mostly controlled by the abundance of Norway rat and house mice, and food availability; the Norway rat by the abundance of black rat, a house mice and of mustelid predators; and house mouse by the other rodents and food availability. These results suggest that several mechanisms could be concurrently controlling abundance of these species; competition and predation for Norway rat, and competition and bottom-up control by environmental filtering for the other two rodents. While different factors explain the abundance of invasive species within the same functional group, food resource availability is, in general, the main controller of abundance of invasive rodents and carnivores in the Azores. Therefore, IAS management actions in these islands should focus on limiting the access to food resources and shelter, mainly near to human populations.

     

Species richness,equitability, and abundance of ants in disturbed landscapes

Ants are used as indicators of environmental change in disturbed landscapes, often without adequate understanding of their response to disturbance. Ant communities in the southeastern United States displayed a hump-backed species richness curve against an index of landscape disturbance. Forty sites at Fort Benning, in west-central Georgia, covered a spectrum of habitat disturbance (military training and fire) in upland forest. Sites disturbed by military training had fewer trees, less canopy cover, more bare ground, and warmer, more compact soils with shallower A-horizons. We sampled ground-dwelling ants with pitfall traps, and measured 15 habitat variables related to vegetation and soil. Ant species richness was greatest with a relative disturbance of 43%, but equitability was greatest with no disturbance. Ant abundance was greatest with a relative disturbance of 85%. High species richness at intermediate disturbance was associated with greater within-site spatial heterogeneity. Species richness was also associated with intermediate values of the normalized difference vegetation index (NDVI), a correlate of net primary productivity (NPP). Available NPP (the product of NDVI and the fraction of days that soil temperature exceeded 25 °C), however, was positively correlated with species richness, though not with ant abundance. Species richness was unrelated to soil texture, total ground cover, and fire frequency. Ant species richness and equitability are potential state indicators of the soil arthropod community. Moreover, equitability can be used to monitor ecosystem change.     

Atlantic oakwoods in Great Britain: Factors influencing their definition,distribution and occurrence

Summary

Atlantic oakwoods are the oceanic oak-dominated woodlands that fringe the western coast of Britain and Ireland and, due to their high humidity and rich and luxuriant lower plant assemblages, have been regarded as ‘temperate rainforest’. However, unlike the similarly iconic Caledonian pinewoods, Atlantic oakwoods have no formal designation or associated woodland classification type, which gives some uncertainty to the extent of the oakwoods habitat on its fringes. This paper examines the various elements central to the concept of an ‘Atlantic oakwood’ and discuses their occurrence in Great Britain.     

Factors influencing the distribution and abundance of diaptomid copepods in high-elevation lakes in the Pacific Northwest, USA

We investigated the impact of abiotic factors and trout density on distribution and abundance of diaptomid copepods in high-elevation lakes in North Cascades National Park Service Complex (NOCA), Washington, USA. The most common large diaptomid, D. kenai (mean length = 1.88 mm), was able to persist over a wide range of abiotic factors, but the small herbivorous diaptomid, D. tyrrelli (mean length = 1.18 mm), was restricted to shallow lakes (maximum depth < ≈ 10 m) with relatively high concentrations of total Kjeldahl nitrogen and total phosphorous. There was a significant negative relationship between the density of D. tyrrelli and the density of large diaptomids ( D. kenai and D. arcticus), which could imply interaction between large and small diaptomids. The abundance of large diaptomids was significantly lower in shallow lakes with high densities of reproducing trout (> 250 fish ha-1) than in fishless lakes, in deep lakes with reproducing trout, or in lakes where trout do not reproduce and are 0periodically stocked with fry at low densities (average 179 fry a-1). In lakes where chemical conditions were suitable for D. tyrrelli, the small diaptomid was often abundant when trout density was high and large diaptomids were either absent or in low abundance. Our research suggests that trout density, nutrient concentration, and lake depth influence the abundance of diaptomid copepods in high lakes in NOCA. This revised version was published online in July 2006 with corrections to the Cover Date.     

Factors influencing the abundance and metabolic capacities of microorganisms in Eastern Coastal Plain sediments

The abundance and metabolic capacities of microorganisms residing in 49 sediment samples from 4 boreholes in Atlantic Coastal Plain sediments were examined. Radiolabeled time-course experiments assessing in situ mirobial capacities were initiated within 30 min of core recovery. Acetate (1-¹⁴C- and³H-) incorporation into lipids, microbial colony forming units, and nutrient limitations were examined in aliquots of subsurface sediments. Water-saturated sands exhibited activity and numbers of viable microorganisms that were orders of magnitude greater than those of the low permeability dense clays. Increased radioisotope utilization rates were observed after 6–24-h incubation times when sediments were amended with additional water and/or nutrients. Supplements of water, phosphate, nitrate, sulfate, glucose, or minerals resulted in the stimulation of microbial activities, as evidenced by the rate of acetate incorporation into microbial lipids. Additions of water or phosphate resulted in the greatest stimulation of microbial activities. Regardless of depth, sediments that contained >20% clay particles exhibited lower activities and biomass densities, and greater stimulation with abundant water supplementation than did sediments containing >66% sands and hydraulic conductivities > 200 μm sec.^?1.     

Secondary succession in disturbed Pinus-Quercus forests in the highlands of Chiapas,Mexico

We present floristic and structural data on serai plant communities (Old-Field, Grassland, Shrubland, and Early Successional, Mid-Successional, and Mature Forest) resulting from the current land use pattern in the Pinus-Quercus forests in the highlands of Chiapas, Mexico. The number of species ranged from 24 in the Old-Field stage up to 100 in the Mature Forest, and the shrub layer was richest in all the forested stands. An almost complete floristic replacement exists between the open and the forested communities. Quercus and Pinus dominate the canopy of old-growth stands, but their recruitment does not occur or is very low in the shade. Vigorous seedlings and saplings of these species are found only in the open serai stages or in forest gaps. Demographic and phytosociological data are used to indicate the successional role of dominant species in the forested stages. Some implications of the regional land use patterns for conservation and succession are discussed.     

Factors influencing herpetofauna abundance and diversity in a tropical agricultural landscape mosaic

Agricultural intensification and the associated factors, including land transformation, are among the major global threats affecting biodiversity especially herpetofauna. However, little information is available about how different factors shape herpetofauna species assemblages in agricultural landscape at different spatial scales from patch (125 – 250m) to the landscape (500 – 1000m). We assessed the diversity of amphibians and reptiles in areas under low and high degrees of agricultural intensification and explored different factors regulating diversity at different spatial scales using four sampling methods. Diversity and abundance of amphibians varied significantly between the two zones, but not for reptiles. Agricultural intensification index (AII), calculated based on agrochemical use and area under agriculture at 250m scale, seemed to affect amphibians both at patch as well as at 500m and 1000m landscape scales. The AII influenced reptilian diversity only at patch and 500m scales. Vicinity of natural forest had a stronger influence on reptilian abundance. Seminatural vegetation impacted herpetofauna diversities at larger spatial scales. The extent of water bodies influenced the reptilian abundance at 250m patch scale and amphibian abundance both at 250m and 1000m scale. Fallow lands affected only reptilian diversity at all spatial scales. Plantation affected amphibian at all scales but reptiles only at the landscape scale. Habitat heterogeneity regulated only amphibian diversity. These results highlight the fact that different patch and landscape-scale factors regulate the diversity of reptiles and amphibians differentially. Such scale-specific information will crucially inform future conservation action for the herpetofauna in the agricultural landscape.     

Factors influencing the abundance of breeding Dippers Cinclus cinclus in the catchment of the River Wye, mid-Wales

The number of breeding Dippers was assessed in relation to environmental features and benthic macro-invertebrates over 220 km of tributaries in or adjacent to the catchment of the Welsh River Wye in 1982. Bivariate regression and multivariate analysis revealed strong correlations between breeding abundance and combinations of variables describing stream-gradient and the relative abundances of larval Trichoptera and nymphal Plecoptera. The results are discussed in relation to aspects of the feeding ecology of breeding Dippers and their nestlings.     

Factors influencing the abundance of Japanese encephalitis vectors in ricefields in India--II. Biotic

The relationship of insect predators and phytoplankton with the abundance of Culex tritaeniorhynchus Giles, Cx. vishnui Theobald and Cx. pseudovishnui Colless mosquito larvae and pupae (Diptera: Culicidae) in ricefields was investigated during three rice growing seasons. Notonectids were the most abundant insect predators, whereas diatoms dominated among phytoplankton. Multiple regression analysis showed that the occurrence of notonectids (both nymphs and adults) was negatively associated with larval abundance. Phytoplankton, especially diatoms and blue green algae (BGA), were found to favour abundance of culicine immatures during Navarai and Kuruvai crops, respectively. Larval gut analysis showed that the intake of algae by late instars was high, with 93%, 58% and 24% of diatoms, BGA and green algae, respectively. Filamentous algae may not necessarily be of nutritive value, but they are observed to form mats, which provide protection to the mosquito immatures from the predators.     

Factors influencing dominance structure of common rodent species in Vietnamese tropical forests

It has been shown that the balance between the common rat species belonging to the genera Maxomys and Niviventer in Vietnam regularly changes depending on the geographical latitude. The highest total rate of the genus Niviventer rats (82% of the total catch) has been observed in the northern region (22°0??N) in the Fansipan highland forests (1800?C2000 m above the sea level) and has gradually decreased southward to its minimal value (1% of the total catch) in the lowland dipterocarp forests of Ma Da (11°10??N). On the contrary, Ma Da, the southernmost point, displays the highest rate of Maxomys rats, which decreases northward, reaching less than 2% in the Fansipan forests. The ecological advantages of these common genera are associated with the specific features of their origin and establishment. A case study of a particular area, the Cat Tien National Park, has demonstrated the effects of forest structure and the degree of its disturbance in the balance between the three dominant species, namely, the rats Maxomys surifer and Niviventer fulvescens and the squirrel Callosciurus flavimanus. An additional factor that influences the populations of the rats in question in local areas is their interspecific interactions with the rats of the genus Rattus.     

Factors influencing the distributional abundance of two trophic guilds of Peruvian cricetid rodents

The distributional abundance of 13 species of southern Peruvian rodents is significantly correlated with altitude and patterns of vegetation but vegetation is a better predictor than altitude. Coincidental reversals in the altitudinal trends of both vegetation and rodents demonstrate that rodents are responding to vegetation patterns. Abundance and diversity of rodents are greatest around 4000 m elevation which coincides with the region of greatest vegetational abundance and seasonally heavy rainfall.
The rodent communities consist of two separate feeding guilds, omnivores and insectivores and these guilds show distinctly different distributional patterns. Insectivorous species are strongly associated with the zone of seasonally heavy rainfall (4000 m) whereas omnivorous rodents are relatively abundant over a broader spectrum of elevations and habitats. In a previous study of these same communities, we showed a correspondence between rodent morphology and their diets. This study reveals a correspondence between distributional abundance of the various species and their diets. We conclude that the distributional abundance of southern Peruvian rodents is related to the physiological constraints imposed by altitude (climate) and the distributional abundance of food resources.     

Environmental factors influencing urchin spatial distributions on disturbed coral reefs (New Caledonia, South Pacific)

Few works have examined the relative contributions of habitat variables to the distribution of coral reef urchins. In the present study, the spatial distribution of two common urchin species (Diadema setosum and Echinometra mathaei) was studied in the fringing reefs of two urban bays in New Caledonia (South Pacific). Urchins were surveyed at 105 stations with contrasted habitat structure/anthropic disturbance levels; 32 environmental variables (water/sediment characteristics, reef structuring species) were considered. Moderate densities were generally observed at station scale (mean 0.5 individuals m^− 2). The combination of univariate and multivariate techniques highlighted patchy distributions for Diadema as well as Echinometra, with distinct species/habitat associations; environmental gradients occurring within the bays did not seem to influence the species patterns. For Diadema, the spatial variability was better explained by sediment type than by biotic cover; increasing densities occurred across habitats with larger sediment sizes and decreasing coral complexity/macrophytes cover. In contrast, the distribution of E. mathaei exhibited weak relationships with habitat variables. In coral reefs, small-scale heterogeneity may thus be responsible for most of urchins spatial variability.     

Factors influencing the species composition,distribution and abundance of benthic invertebrates in the profundal zone of a eutrophic northern lake

Factors influencing the species composition, distribution and abundance of benthic invertebrates were determined in a eutrophic subarctic lake from April 1978 to April 1979. Collections were made at five stations located at depths of 4 to 13 m. The largest populations of up to 5 × 10³ animals m^–2 were found in the deepest part of the lake. of the 24 species recorded in this area, the chironomidsProcladius denticulatus, Dicrotendipes modestus, Chironomus decorus andGlyptotendipes barbipes were most common. The strong development of benthos in the profundal zone was attributed to a consistently large supply of food and warm (4 °C) winter temperatures on bottom. Slightly smaller populations (up to 4 × 10³ animals, m^–2), composed of 19–23 species, occurred in shallower water, a reflection of lower (1.5 °C) winter temperatures. In the anoxic northern part of the lake, only 4–8 species were found in low numbers (400–1 000 animals m^–2). This was likely due to low (<5% saturation) oxygen levels in water and high organic content (18.5%) of the sediments.     

Factors influencing the abundance of Trioxys pallidus,a successful introduced biological control agent of walnut aphid in California

This field study reports on factors influencing the abundance of Trioxys pallidus 35 years after its successful introduction in California, and in the presence of continued hyperparasitism and intraguild predation. The seasonal activity of Chromaphis juglandicola and T. pallidus were monitored in 2005–06 in relation to hyperparasitism and mummy predation in three orchards. Walnut aphids remained under the economic threshold in all three orchards with insecticide treatments for other pests in some cases reducing aphid populations as well. No significant density-independent or density-dependent aggregation in the risk of hyperparasitism was found at the individual tree scale, suggesting the absence of a refuge from hyperparasitism. In contrast, significant negative density-dependent aggregation in the risk of intraguild predation was found, but no density-independent aggregation, suggesting a refuge at higher mummy densities. Using a linear mixed effects model, the following factors were found to influence mummy density: aphid density from the previous sample date and intraguild predation, with the latter linked to hyperparasitism from the previous sample date through a significant interaction that appears to be mediated by current aphid density.