Fine-scale habitat structure complexity determines insectivorous bird diversity in a tropical forest

Habitat complexity in reforested stands has been acknowledged as a key factor that influences habitat use by birds, being especially critical for habitat disturbance-sensitive species such as tropical understory insectivorous birds. Most studies regarding the relationship between forest structure and species diversity were conducted at the landscape scale, but different diversity patterns may emerge at a finer scale (i.e., within a habitat patch). We examined a tropical reforested area (State of Caldas, Colombia), hypothesizing that insectivorous bird richness, abundance, and foraging guild abundance would increase as intra-habitat complexity increases. We established 40 monitoring plots within a reforested area, measured their structural features, and determined their relationships with species richness, total abundance, and foraging guild abundance, using Generalized Additive Models. We found that the increasing variation in basal area, stem diameter, and number of stems was positively correlated with species richness, total abundance, and foraging guild abundance. Relationships between richness or abundance and structural features were not lineal, but showing curvilinear responses and thresholds. Our results show that heterogeneity on basal area, stem diameter, and the number of stems was more correlated to insectivorous bird richness and abundance than the average of those structural features. Promoting structural variation on reforested areas by planting species with different growth rates may contribute to increase the richness and abundance of a tropical vulnerable group of species such as the understory insectivorous birds.     

Numerical variation in three coexisting macrodetritivore species (Proasellus coxalis,Planorbarius corneus and Bithynia tentaculata) under different levels of vertical forces in aquatic microcosms

Laboratory experiments were conducted to assess the impact of both top-down and bottom-up forces on simplified macrodetritivore guilds. Three macrodetritivore species of Lake Albano (central Italy) were used: Proasellus coxalis, an isopod, and Planorbarius corneus and Bithynia tentaculata, two snails. They were stocked at the ratio of 32:160:164 individuals in each of 24 aquaria. The simplified guilds were governed by different vertical pressures. Three types of top-down (predation) pressures, viz. (i) absence of predators, (ii) high density of the predator Erpobdella octoculata, a leech, (iii) high density of Erpobdella and Gambusia affinis, a fish, and two types of bottom-up pressures, viz. high and low leaf-detritus availability, were employed. The effects of vertical forces were determined by the numerical variation in the survivors of each species and the ratio between the survivors of the three species of macrodetritivores. A quantitative index of the daily top-down force (TDF) was computed. The results showed that the three coexisting macrodetritivore species were sensitive to vertical pressures. When increasing the top-down pressure in aquaria with high detritus availability, the guild response was non-linear: (i) in absence of predators, the percentage of the survivors of the three macrodetritivore species was the highest; (ii) the presence of Erpobdella reduced the macrodetritivore abundance and (iii) the set of aquaria with coexisting Erpodella and Gambusia significantly increased the number of survivors of the three macrodetritivore species when compared top aquaria with Erpobdella. On the contrary, in aquaria with low detritus availability, the increase of the top-down pressure caused no significant variation in the number of surviving species.     

Vertical stratification of beetles in tropical rainforests as sampled by light traps in North Queensland,Australia

How arthropods are distributed within the vertical structure of tropical rainforests is of considerable interest to ecologists. Here, we examine how light trapped beetles are distributed in tropical rainforest in North Queensland, Australia. In January and July 2012, traps were suspended 0 m, 10 m, 20 m and 30 m above the ground in five locations with no more than one trap at any single location on any night. Maximum canopy height at the sites was 35 m. A total of 7299 individuals of 492 morphospecies and 66 families were collected. The species abundance‐based coverage estimator predicted a total species richness of 765. Sample completeness decreases with increasing height from the ground suggesting higher strata were less well sampled. Distance‐based redundancy analysis showed species richness was significantly different between 30 m and all other levels but not between other paired strata. In contrast, both species composition and family composition were significantly distinct for all strata pairs except 10 m with 20 m, and 20 m with 30 m, suggesting that the most distinct strata were 0 m and 30 m. The first two axes of ordination and hierarchical clustering accounted for 46.5% and 17.4% of species composition variation corresponding with season and stratum, respectively. Family level analyses gave similar results to those at the species level. We found stratification of different feeding guilds with herbivores comprising a larger percentage of species in higher strata, whereas saprophages were restricted to the lower strata, reflecting the availability of key resources for these guilds. Fewer species or families were found to be indicators of strata, as measured using IndVal, than for Malaise and flight interception traps (FIT). Dytiscidae and Hydraenidae were abundant but had not been collected using Malaise and FIT. Which species or families are indicators of strata depends on sampling method suggesting multiple sampling methods should be used to establish indicators.     

Conversational Noise Reduction as a Win–Win for Ecotourists and Rain Forest Birds in Peru

For all its positive attributes, the recent expansion of ecotourism has resulted in greater influxes of people into natural areas, causing a range of impacts including behavioral disruptions among wildlife. How animals respond to conversation is poorly understood, but noise reduction may reduce the impact of ecotourists while simultaneously enhancing their experience with higher wildlife encounter rates. We tested the response of a rain forest bird community to noise by playing a recorded conversation while conducting point censuses in a terra firme forest in Tambopata, Peru. Fifty decibel conversation (approximately library speaking volume) caused declines of 35 percent in total detections and 33 percent in detected species richness. Birds reacted similarly to 60 dB (approximately the volume of an excited child): average detections declined by 39 percent and detected species richness by 37 percent. Specifically, noise‐induced detection declines were manifest both in decreased vocalizations (37% decline) and decreased physical sightings (44% decline). Lowered detection frequencies indicate behavioral shifts. As vocalization is involved in territory defense, breeding behavior, and predator detection, strong noise responsiveness indicates potential harm for birds. Insectivores were the most affected bird guild, raising conservation concerns, as insectivorous birds are sensitive to habitat modification. Birds reacted strongly to noise both near an established ecotourist lodge and in an intact reserve, indicating an absence of habituation. Thus, as a method for reducing ecotourism's footprint on native fauna and improving tourist satisfaction with increased wildlife sightings, noise reduction seems promising, even for well‐established ecotourist lodges.     

Cascading effects of cannibalism in a top predator

1. Predator interactions are often driven by size differences, with larger predators consuming smaller ones. Cannibalism is widespread among predators, and can be more intense than antagonistic interactions between different predator species. 2. In a series of greenhouse experiments and a field experiment, we investigated the role of size structure in shaping the impacts of a top predator (the wandering spider Cheiracanthium mildei L. Koch) on an insect herbivore in vineyards of Napa County, California. 3. In greenhouse cages, survival of small C. mildei was lower when large C. mildei were present, and the combined effects of small and large C. mildei on leafhopper numbers and grape leaf damage were non‐additive. The frequency of cannibalism in C. mildei did not change when the abundance of leafhoppers was manipulated. However, in the field experiment small and large C. mildei combined additively to reduce leafhopper numbers. 4. Results show that cannibalism has the potential to dampen the cascading effects of C. mildei in a vineyard food web, but that it may be less important than other mortality factors in the field. Nonetheless, C. mildei substantially impacted leafhoppers in both the greenhouse and the field, suggesting that mortality caused by cannibalism or other factors may not compromise its overall predatory impacts.     

Disturbance-induced bird diversity in early successional habitats in the humid temperate region of northern Japan

The positive role of moderate natural disturbance is less known for a mobile organism such as birds, compared to sessile organisms. In the face of recent declines of grassland birds, it is necessary to identify the mechanism to maintain avian diversity in early successional open habitats in different regions. In the humid temperate region, the predominant habitat type is woody vegetation. Therefore, bird communities were studied along vegetational succession using a chronosequence method. TWINSPAN identified three distinctive habitat types (barren, grass-fen and shrubland) and four habitat guilds of birds (pioneer, grassland, ubiquitous and shrub) in the study sites. Path analysis determined the direct and indirect effects of disturbance on the habitat guilds of birds. Short and intermediate intervals of the water disturbance are important to pioneer guilds and grass-fen habitat, respectively. The frequent occurrence of large animals had a negative impact on grassland guild. It suggests that grassland birds less tolerate cattle grazing or human activities in a region with intensive land use. The chronosequence study revealed the dynamic nature of the bird community. Birds occupy habitats following the successional sere of vegetation, responding to animal occurrence and human activities in various manners.     

The large carnivores from ‘Ubeidiya (early Pleistocene, Israel): biochronological and biogeographical implications

The archaeological site of ‘Ubeidiya provides a unique, rich faunal assemblage, as well as evidence for the presence of early hominins in the Levant. Paleontological analysis of the faunal community is pertinent to understanding the biochronology and the timing of hominin dispersal events from Africa to Eurasia. This study presents the large carnivores from the recent seasons of excavations (1989-1999) and previously published material. Based on biochronological correlations of the carnivore guild and paloemagnetism, the age of the site is 1.5-1.2 Ma. This date is 100-200,000 years earlier than previous estimates. Of specific importance is the presence of the African origin saber tooth Megantereon cf. M. whitei and the Eurasian origin canids Canis moschbachensis and Lycaon lycoanoides.     

Classification of the terrestrial habitats on Marion Island based on vegetation and soil chemistry

Abstract. Soil chemistry and vegetation data for 176 sites on sub‐Antarctic Marion Island (47° S, 38° E) were subjected to Canonical Correspondence Analysis. 21 habitats in six habitat complexes were recognized from a clustering analysis of the site scores on the canonical axes. Another two habitats and one habitat complex were added to this. The resultant habitat classification closely reflects the between‐habitat variation in the relative magnitudes of the main forcing variables that determine ecological succession on the island (moisture, exposure, parent soil material, salt‐spray and manuring and trampling by seals and seabirds). It can be used by persons with a minimum of botanical or soil expertise. The habitat complexes (number of habitats in complex) are: Coastal Salt‐spray Complex (2); Fellfield (2); Slope (6); Biotic Grassland (3); Biotic Herbfield (3); Mire (6); Polar Desert (1). A key is provided whereby the habitat to which a particular site belongs can be determined using botanical criteria, although infrequently soil moisture and pH information is also needed. Summaries of the soil chemistry and vegetation characteristics of the various habitats are also provided.     

Sessile rotifers (Rotifera) exhibit strong seasonality in a shallow,eutrophic Ramsar site in Mexico

To better understand the sessile rotifer community of a shallow, eutrophic lake, we monitored over a 1‐year period the monthly changes in the density and diversity of rotifers on the roots of the common water hyacinth, Eichhornia crassipes, which served as a representative hydrophyte. Selected physical and chemical parameters of the water were also determined. Mean annual density of all sessile species was 630 individuals per ml. Species of Collothecacea (n = 7) were most abundant. Of the 12 species of Flosculariaceae (Flosculariidae), Sinantherina socialis occurred seasonally, while Ptygura beauchampi was most common across all seasons. The Shannon–Wiener diversity index was highest (H′ = 2.8) in April, but decreased in January (H′ = 1.3). Applying the concept of the guild ratio (functional‐based analysis) we found that raptorial species (Collothecacea) were dominant over most of the year (June–February), while microphagous Flosculariidae were dominant during the warm, drier season (March–May). BEST (optimal matching of biota to environment, including stepwise search) analysis and canonical correspondence revealed that temperature, dissolved oxygen, pH, turbidity, and transparency strongly influenced sessile rotifer dynamics. We also found significant correlations between the density of some species and physicochemical variables. These species included Collotheca ambigua, C. coronetta, C. ornata, C. campanulata, C. tenuilobata, and Stephanoceros millsii in the Collothecacea; and Beauchampia crucigere, Limnias melicerta, L. ceratophylli, Ptygura crystallina, P. melicerta, and Sinantherina ariprepes in the Flosculariidae. Our study shows that the communities of sessile rotifers were structured by abiotic factors and that the guild ratio is useful for understanding the relationship between sessile rotifers and their substrata.