Microzooplankton as an indicator of environmental quality at an industrial complex in the Brazilian Amazon

The large volume of water in the Pará River, together with governmental incentives, has attracted many industries to the city of Barcarena, Brazil. This industrial activity has the potential to cause changes to aquatic environments. Zooplankton species are considered good indicators of environmental changes. We assessed the association between changes in community composition and proximity to an industrial-port complex, and identified potential bioindicator species in these environments. Five quarterly sampling points were selected along the Pará River (P1–P5) in 2012. The zooplankton community in this region is composed of 64 species. The highest total densities were recorded in February and November, which are both during the rainy season. Zooplankton density was greatest at P3, which was near an industrial-port complex, suggesting that industrial activity affected zooplankton density. An IndVal test showed the rotifer Filinia opoliensis (r = 0.86, p = 0.02) to be a possible bioindicator of environmental quality in the study area. This paper contributes to the discussion of the impacts of installing industrial plants and large ports in the Amazon.     

Independence of total species richness and richness difference are not the same thing

Leprieur and Oikonomou (2014) criticized that a replacement index β_− 3, a partitioned component of Jaccard index β_jac, was not richness independent and should not be used in biogeographic and ecological studies. However, Leprieur and Oikonomou failed to recognize the difference between richness and richness difference. Independence of total species richness is not equal to independence of richness difference. Theoretically and ideally, it is true that β_− 3 (and β_jac as well) is not independent of richness difference while Simpson index (β_sim) is fully independent of richness difference. However, all these indices actually are independent of total species richness. At last, it is worth mentioning that the ideal independence studied here is easily violated in computational simulation and real-world settings.     

Frugivorous birds visit fruits of emerging alien shrub species more frequently than those of native shrub species in the South African Mediterranean climate region

We compared daily visitation frequency indices by 4 large (> 150 g), 7 medium-size (50–150 g), 5 small (30–50 g) and 8 and tiny (< 30 g) frugivorous bird species on fleshy fruits of two native shrubs (Olea europaea subsp. africana and Chrysanthemoides monilifera subsp. monilifera), two established alien shrubs (Solanum mauritianum and Lantana camara) and two emerging alien shrubs (Myoporum tenuifolium and Pittosporum undulatum) at nine different sites in the Cape Floristic Region. Large, medium-size and tiny birds as groups displayed significantly higher visitation frequency indices on fruits of both emerging alien shrub species than the other shrub species. Small birds as a group displayed insignificantly different visitation frequency indices on fruits of both emerging and established alien shrub species but significantly higher visitation frequency indices on fruits of both emerging and established alien shrub species than on fruits of the native shrub species. However, there were significant differences in foraging frequency indices of the bird species included within each of these body size groups on fruits of the different shrub species. Among the large birds, Columba guinea and among the medium size birds Sturnus vulgaris, Streptopelia senegalensis, Turdus olivaceus and Onychognathus morio all exhibited significantly higher visitation frequency indices on fruits of both emerging alien shrub species than on fruits of the other shrub species. These findings indicate that alien plant control measures should be focused on eradicating localised populations of emerging aliens to limit preferential consumption of their fruits by birds and consequent dispersal of their seeds that germinate readily into natural areas.     

Zooplankton assembly in mountain lentic waters is primarily driven by local processes

The influence of local (i.e. physico-chemical constraints) and regional (i.e. dispersal) processes in determining the structure of zooplankton communities in lentic waters was analysed in a mountain district of 4500 km² (northern Apennines, Italy). In the 47 lakes and ponds considered in this study, a total of 139 taxa were found. Surface area (SA) and maximum depth (Z_max) significantly influenced species richness and nestedness, stressing the importance of habitat availability for zooplankton diversity and composition. Species richness and nestedness did not correlate with site isolation, indicating low influence of dispersal for these community properties. A negative relationship between the similarity in species composition among sites and their mutual geographic distance was also found. The relative importance of different sources of compositional variation was quantified by direct ordination. Local environmental conditions (i.e. Z_max, altitude, pH and conductivity) accounted for 65.9 % of the variation in rotifer assemblages. The importance of environmental constraints in structuring zooplankton communities was best documented by the microcrustacean distribution in the study area, which was mainly correlated (73.4 % of the variation in the species data) with water ionic content, surface area and hydroperiod of the habitats.Although previous studies on processes shaping zooplankton assemblages that operate at different scales have yielded contrasting results, our data provide clear evidence for a major role of local constraints.     

Multi-scale comparison of topographic complexity indices in relation to plant species richness

Topographic complexity is a key component of habitat, which has been linked to increased species richness in many ecological communities. It can be measured in various ways and it is unclear whether these different measurements are mutually comparable when they relate to plant species richness at different spatial scales. Using a densely sampled set of observations for Rhododendrons (406 species and 13,126 georeferenced records) as a test case, we calculated eight topographic complexity indices from a 250-m resolution digital elevation model and examined their correlations with Rhododendron species richness in China at seven spatial scales: grain sizes 0.05°, 0.1°, 0.25°, 0.5°, 1.0°, 1.5°, and 2.0°. Our results showed that the eight topographic complexity indices were moderately to highly correlated with each other, and the relations between each pair of indices decreased with increasing grain size. However, with an increase in grain size, there was a higher correlation between topographic complexity indices and Rhododendron species richness. At finer scales (i.e. grain size ≤ 1°), the standard deviation of elevation and range of elevation had significantly stronger correlations with Rhododendron species richness than other topographic complexity indices. Our findings indicate that different topographic complexity indices may have positive correlations with plant species richness. Moreover, the topographic complexity–species richness associations could be scale-dependent. In our case, the correlations between topographic complexity and Rhododendron species richness tended to be stronger at coarse-grained macro-habitat scales. We therefore suggest that topographic complexity index may serve as good proxy for studying the pattern of plant species richness at continental to global levels. However, choosing among topographic complexity indices must be undertaken with caution because these indices respond differently to grain sizes.     

Adult odonate abundance and community assemblage measures as indicators of stream ecological integrity: A case study

Water resources demand constant conservation actions due to several problems (e.g. riparian vegetation cut-off, construction of dams, acidification, sewage and pesticide spills) that degrade the aquatic systems worldwide and affect its physicochemical parameters and habitat characteristics. Odonata is a potential group of organisms that could indicate these habitat alterations once they have aquatic and terrestrial life forms. In this study, we tested the use of adult odonate individual species and community assemblage measures to evaluate the effect of riparian vegetation cut-off and sewage discharges. The study was performed at Turvo Sujo River, in Viçosa, Southern Brazil. We selected twelve sites, six of them were upstream and six were downstream the city. Species abundance and species richness estimates of adult odonates were performed on sunny days during summer and winter. We analyzed the goodness-of-fit of the species abundances to geometric and lognormal series. We also measured the Habitat Physical Integrity Score (HPIS), pasture and forest proportions and physicochemical water parameters at each site. Only few species were abundant in up- and downstream regions. Abundance of Argia modesta was higher at the upstream (t = 3.188; df = 17; p = 0.005) than at the downstream region and this species is a potential habitat bioindicator organisms. Species richness was statistically different only in the wet season and species–abundance relations at the two regions fitted well to both geometric and lognormal series. The lack of riparian vegetation indicates a loss of habitat integrity and heterogeneity at Turvo Sujo River basin, which was mainly dominated by lake-dwelling odonate species. Low species richness differences are caused by species pool biases toward those ones capable to survive at degraded ecosystems, suggesting that the effects of water parameters are much less important than a landscape dominated by pastures and practically without forests. We suggest the use of species–abundance models (like geometric and lognormal series) to determine the degree of impacts over a given community once they are simple models and can show intrinsic processes structuring communities.     

Biased richness and evenness relationships within Shannon–Wiener index values

The purpose of this analysis was to empirically model and graphically illustrate the numerical relationships between richness (S, 4–35 species) and evenness (E) with respect to Shannon–Wiener index (H′, log_e-based) values. Thirty-two richness-based third-order polynomial regression models (R > 0.99, P < 0.001, n = 28–71) were constructed to characterize these relationships. A composite diagram showed richness varied curvilinearly, with steepness increasing and the spacing between curves decreasing with greater evenness and H′. Maximum H′ values for each richness curve were equal to log_e S (when E = 1), whereas minima were approximated by evenness values of ∼1/S (when H′ = 0). It was concluded from multiple and polynomial regression analyses that: (i) evenness contributed more than richness (E:S ≥3:1) to determining H′, based on standardized partial beta-coefficients; (ii) the differential in E:S ratios increased with greater richness; (iii) the patterns of H′ sample variation between maximum unevenness and perfect evenness was convexo-concave shaped; and (iv) richness as an explanatory variable of H′ was likely an artifact of evenness (0–1 scale) being rescaled according to individual H′ maxima. H′ was redefined as a logarithm-weighted measure of evenness at a given level of richness, which means H′ is either an imperfect index of diversity or a biased measure of evenness. It was also found that the fundamental components of the Shannon–Wiener index measure dominance concentration rather than evenness, with the reversal in emphasis due to multiplication of the H′ equation by −1. H′-derived effective species numbers (exp H′, D) increasingly deviated from those of the diversity model D = S × E in response to increasing richness (up to 69% for 35 species), particularly when evenness was between 0.15 and 0.40. Of two cross-validated H′ prediction methods (P < 0.001, n = 325), the collective use of individual richness-based polynomial regression equations (r = 0.954) was better than a single multiple regression model that incorporated a broad spectrum of richness levels (r = 0.882). A simple graphic model was constructed to illustrate patterns of evenness variation as a function of changing richness and H′ values. Based on the identified biases, particularly E:S ratios, it was recommended that use of H′ be discontinued as a basis for assessing diversity in ecological research or, at the very least, accompanied by independent analyzes of richness and evenness.     

Taxonomic diversity and community structure of arbuscular mycorrhizal fungi (Phylum Glomeromycota) in three maritime sand dunes in Santa Catarina state,south Brazil

Community structure and species richness of arbuscular mycorrhizal fungi (Phylum Glomeromycota) were studied in sand dune sites at Itapiruba (southern), Joaquina (intermediate) and Praia Grande (northern) beaches along the coast of the state of Santa Catarina, Brazil. In each site, a 20 × 20 m plot was established and 20 soil samples collected in a regular grid pattern. Fungal spores were extracted from each sample, counted and identified to species level. A total of 25 species were recovered belonging to seven genera and five families in the Glomeromycota. Gigaspora albida and Acaulospora scrobiculata occurred in >50 % of samples at all three sites. Other common species whose sample frequency was >50 % in one or two sites were Scutellospora weresubiae, Scutellospora cerradensis and Racocetra gregaria, while the remaining majority of species were detected in <25 % of samples within a given site. Dune sites could be differentiated based on the higher frequency of occurrence of S. cerradensis and Acaulospora morrowiae in Itapiruba, S. weresubiae in Joaquina, and Scutellospora hawaiiensis in Praia Grande. No differences across sites were observed for species richness and total spore numbers, the latter averaging from 28.8 to 31.8 spores per 100 ml soil. Shannon diversity was significantly higher in Praia Grande compared to the other two sites. Differences in the relative spore abundance of genera among dunes were detected only for Scutellospora, which was significantly more abundant in the Joaquina beach. Community structure, as depicted by species rank/log abundance graphs, was not significantly different between areas according to the Kolmogorov–Smirnov two-sample test. Species accumulation curves demonstrated that 13 samples were enough to detect 90 % of all species. Overall, sand dune systems share similar arbuscular mycorrhizal fungal communities despite being geographically distant (150 km) from each other.     

Zooplankton Diversity of Osmansagar Reservoir,Telangana, India

Zooplankton composition and diversity in Osmansagar reservoir, Telangana, India were investigated during the year 2010–2012. Collected data revealed the occurrence of 66 species of zooplankton, of which 50 rotifers, 14 cladocerans and two copepods. The population density of zooplankton varied from 83 to 1080 Ind./L. The highest density was due to rotifer and copepod population. Diversity (H′) was ranged from 0.679 to 2.631, evenness (J′) was 0.257 to 0.904 and species richness was 8–24. The less diversity and evenness was observed in November 2011, March and August 2012, because of copepoda dominance by Mesocyclops leuckarti. The population abundance of zooplankton was Brachionus forficula, Brachionus diversicornis, Brachionus calyciflorus, Keratella tropica, Trichocerca similis and Diaphanosoma sp. especially during the summer seasons in both the years. There was no seasonal periodicity of any zooplankton communities, but the population turnover was observed from rotifers to copepoda over the study period. The significant inter and intra relationship between and within physicochemical and zooplankton indices were noted. It is found that surface water temperature, magnesium and total hardness could be a limiting factor for the species richness. Dominance may be due to the numerical abundance of rotifer and copepod and it has a positive significant correlation with pH.     

Role of macrophytes as microhabitats for zooplankton community in lentic freshwater ecosystems of South Korea

Zooplankton community distribution depends largely on the microhabitat characteristics of the water body. It has been reported that macrophytes provide microhabitats for zooplankton (e.g., space and food resources). To date, studies have focused on the overall influence of macrophytes on zooplankton (e.g., positive relationships with zooplankton diversity); however, the morphological characteristics of macrophytes have not been intensively studied. To fill this gap in knowledge, we investigated zooplankton abundance and diversity, macrophyte characteristics (types, dry weight, and species number), and physicochemical parameters (water temperature, dissolved oxygen, pH, conductivity, and chlorophyll a) by using the 1 × 1 m quadrat method. We surveyed 164 wetlands in South Korea during spring (May to June), prior to the summer monsoon. Patterning zooplankton distribution was accomplished using a Self-organizing map (SOM). We used 34 input variables (zooplankton genera) to train the model. The distribution of five plant habit parameters (no plant, emergent, free-floating, floating-leaved, and submerged) was investigated with a trained SOM plane, by environment data masking. Based on a U-matrix, three clusters were identified from the model. Zooplankton assemblages were positively related to macrophyte characteristics (i.e., dry weight, species number, and plant type). In particular, free-floating plants supported rotifers, such as Testudinella, and cladocerans, such as Alona, Chydorus, Diaphanosoma, and Ilyocryptus (mostly epiphytic). Submerged plants were associated with planktonic rotifers, such as Filinia, Ploesoma, Synchaeta, cladocerans, such as Daphnia, and copepods, such as Eucyclops and Macrocyclops. On the basis of these results, we suggest that the microhabitat structure, created by macrophytes, is an important factor in determining the diversity and abundance of zooplankton communities, because the different species compositions of macrophytes support diverse zooplankton genera in these habitats. The results indicate that macrophytes are the key components of lentic freshwater ecosystem heterogeneity, and the inclusion of diverse plant species in wetland construction or restoration schemes will result in ecologically healthy food webs.     

Three heat shock proteins are essential for rotifer thermotolerance

Heat shock proteins (HSPs) are important molecules in the stress response of organisms from prokaryotes to mammals, and thus may be useful biomarkers for environmental stress. Here we characterize the functional roles of genes belonging to four distinct families of HSPs (hsp40, hsp60, hsp70, and hsp90) in the monogonont rotifer Brachionus manjavacas. Because B. manjavacas inhabits ponds of varying thermal regimes, including ephemeral ponds that may experience temperature fluctuations, HSP-mediated thermotolerance likely is important to its survival and adaptation. Using interference RNA (RNAi), we provide the first conclusive evidence that HSPs are required for rotifer survival following heat stress. Effective RNAi-mediated suppression of all hsp genes except hsp90 was verified via quantitative PCR. Hsp40, hsp60, and hsp70 are required for rotifer thermotolerance (P < 0.05); however, our data do not indicate hsp90 is essential. Quantitative PCR further revealed immediate up-regulation of hsp40 mRNA following heat stress. Additionally, we demonstrated expression of hsp40 mRNA in multiple tissues using fluorescent in situ hybridization. Our characterization of mRNA expression and functional roles for four distinct hsp genes provides a baseline for molecular-level comparisons of the stress response of rotifers with other taxonomic groups, and the technique for in-depth studies of the role of specific genes in rotifer stress responses. Considering the potential for ambient temperatures to impact species survival, competitive interactions, and body size of individuals, thermotolerance may be an important influence on zooplankton community structure.     

A comparison of algal,macroinvertebrate, and fish assemblage indices for assessing low-level nutrient enrichment in wadeable Ozark streams

Biotic indices for algae, macroinvertebrates, and fish assemblages can be effective for monitoring stream enrichment, but little is known regarding the value of the three assemblages for detecting perturbance as a consequence of low-level nutrient enrichment. In the summer of 2006, we collected nutrient and biotic samples from 30 wadeable Ozark streams that spanned a nutrient-concentration gradient from reference to moderately enriched conditions. Seventy-three algal metrics, 62 macroinvertebrate metrics, and 60 fish metrics were evaluated for each of the three biotic indices. After a group of candidate metrics had been identified with multivariate analysis, correlation procedures and scatter plots were used to identify the four metrics having strongest relations to a nutrient index calculated from log transformed and normalized total nitrogen and total phosphorus concentrations. The four metrics selected for each of the three biotic indices were: algae—the relative abundance of most tolerant diatoms, the combined relative abundance of three species of Cymbella, mesosaprobic algae percent taxa richness, and the relative abundance of diatoms that are obligate nitrogen heterotrophs; macroinvertebrate—the relative abundance of intolerant organisms, Baetidae relative abundance, moderately tolerant taxa richness, and insect biomass; fish—herbivore and detritivore taxa richness, pool species relative abundance, fish catch per unit effort, and black bass (Micropterus spp.) relative abundance.All three biotic indices were negatively correlated to nutrient concentrations but the algal index had a higher correlation (rho = ?0.89) than did the macroinvertebrate and fish indices (rho = ?0.63 and ?0.58, respectively). Biotic index scores were lowest and nutrient concentrations were highest for streams with basins having the highest poultry and cattle production. Because of the availability of litter for fertilizer and associated increases in grass and hay production, cattle feeding capacity increases with poultry production. Studies are needed that address the synergistic effect of poultry and cattle production on Ozark streams in high production areas before ecological risks can be adequately addressed.     

A probability distribution model of small -scale species richness in plant communities

We devised a probability distribution model that best expressed species richness per quadrat in grassland communities, and clarified the mechanism by which the mean richness per quadrat was always larger than the variance among quadrats. Our model will aid in the understanding of community structures, and allow comparisons among different communities. The model was constructed based on relatively simple theoretical assumptions about the mechanisms in play in target communities. We assumed in the model that the number of species occurring in an actual quadrat, j, is the sum of “the fundamental number of species”, k (constant), and “a fluctuating number of species”, i (a Poisson variate with the mean of μ); that is, j = k + i, where i, j and k are non-negative integers. The probability that j species occur in a quadrat is given by a Poisson-like distribution (extended Poisson), with two parameters k and μ. The mean species richness in the probability distribution is expressed by λ (= k + μ), and the variance is λ − k. The proposed model afforded a good fit for the observed frequency distribution of species richness per quadrat. If even one species is common among many quadrats, the mean number of species per quadrat is greater than the variance. The greater the number of common species among quadrats is, the larger is the value of k, and then the more pronounced is the difference between the mean and the variance (although the variance does not change). We fitted the model to 55 datasets collected by ourselves from grasslands in various locations (Tibet, Inner Mongolia, Slovakia, or Japan), with varying quadrat size (0.25, 0.0625, or 0.01 m²), and under differing management status (various stocking densities).     

Altitude modifies species richness–nutrient indicator value relationships in a country-wide survey of grassland vegetation

Nutrient enrichment is a threat to botanical diversity in Europe, and its assessment is part of biodiversity monitoring schemes. In Switzerland, this is done by calculating the average nutrient (N) indicator value of the vegetation based on a country-wide systematic vegetation survey. However, it is questionable whether N values indicate eutrophication and resulting species loss equally well across an entire country, which includes wide topographic gradients and distinct biogeographic regions. Here we analyze vascular plant species lists from 415 grassland plots (10 m²) between 365 and 2770 m a.s.l. throughout Switzerland to investigate how the relationship between N value and species richness differs with altitude and among regions. The N value strongly decreased with altitude (piecewise regression: r² = 0.77), particularly between 800 and 2000 m a.s.l., where this decrease was related to a decreasing proportion of fertilized grasslands. In the alpine belt, lower N values were associated with a greater frequency of acidic soils and a restricted species pool. Vascular plant species richness was maximal at intermediate altitude (piecewise regression: r² = 0.33) and intermediate N value (polynomial regression: r² = 0.46). When analyzed separately by altitudinal belt, the relationship between species richness and N value was negative in the lowlands and montane belt but unimodal in the subalpine belt. In the alpine belt, soil pH (R indicator values) explained most of the variation in species richness. Two indices of between-plot diversity (floristic dissimilarity and the contribution of individual plots to total species richness) were negatively related to N values from the lowlands to the subalpine belt but not in the alpine belt. All relationships differed little among the biogeographic regions of Switzerland, but they might be modified by changes in management and by the expansion of common lowland species into mountain grasslands.     

Impacts of small hydropower plants on macroinvertebrate communities

Several nitrogen (N) field experiments were carried out in Nanjing and Anyang, China, to study the dynamic characteristics of biomass accumulation and N uptake, and to define the dilution curve for critical N concentration in cotton reproductive organ over the growth period. The results show that the total biomass and N accumulation were affected significantly by the rate of N application, exhibiting a sigmoid curve over time. The beginning time of fast N accumulation was 1–5 d earlier than that of biomass accumulation. The cotton lint yield was correlated with N concentration in the reproductive organ and fluctuated with varying N concentration, indicating the existence of luxurious N consumption in the cotton reproductive organ. The N concentration increased with increasing N application rates, and decreased gradually during the growth period. The relationship between biomass and N concentration can be described with a power equation. The patterns of the N concentration dilution model were consistent at both experimental sites, but the model parameter values of a differed. The results presented in this paper indicate that a critical N concentration dilution curve for cotton reproductive organ is independent of ecological region and can be described with a power equation.     

引水型电站对河流底栖动物群落结构的影响

于2005年10月对香溪河干流5个小水电站对河流底栖动物的影响进行调查研究,按影响情况,各电站设5个采样点.应用底栖动物物种组成、现存量、优势类群、功能摄食类群等参数,衡量小水电站对河流底栖动物群落结构的影响.在研究区域共采集到底栖动物4656条,平均密度为658ind./m2,蜉蝣目的四节蜉属(Baetis spp.)是该区域的优势类群.研究结果表明:电站的修建对河流水化学指标没有显著影响,但河流生境的物理因子(如流速和水深)都发生了较大的改变;对河流底栖动物的各方面均有一定的影响,特别是密度在5个样点间差异显著,而功能摄食类群中滤食者和捕食者的百分含量也有明显差异.另外,各项指标在5个样点间均有一致的变动趋势.相似性分析表明,坝下3号样点的群落组成差异最大,这意味着完全阻隔的坝不利于河流生物多样性的保护.     

Morphology and bloom dynamics of Cochlodinium geminatum (Schütt) Schütt in the Pearl River Estuary,South China Sea

An unarmored dinoflagellate bloom of Cochlodinium geminatum (Schütt) Schütt has been identified in the Pearl River Estuary, South China Sea during the severe dry season, from late October to early November, 2009, when temperature and salinity ranged between 20.0–27.2 °C and 10.6–33.4, respectively. Light and scanning electron microscopy were used to identify the characteristics of C. geminatum and provided the clear morphological structure for this species. The organism was primarily found in chains of two cells or single cell, and no longer chains were observed. Cells were irregularly spherical or slightly dorso-ventrally, with size ranged between 28 and 36 μm and longer than wide. A large nucleus in the center with numerous golden chloroplasts was present, and the cingulum made 1.5 turns around the cell. The concentration of C. geminatum ranged from 10² to greater than 10⁷ cells l⁻¹ during the bloom period. Nutrient concentration ranges during the bloom were 1.29–81.00 μM NO₃, 0.14–12.14 μM NO₂, 0.21–6.29 μM NH₄, 0.23–6.26 μM PO₄ and 3.29–171.43 μM SiO₃, respectively. Total biomass expressed in terms of chlorophyll a ranged from 2.44 to 135.45 μg l⁻¹, with an average 19.9 μg l⁻¹ in surface water throughout the PRE. Two main clusters corresponding to the water sectors were defined with multivariate analysis (cluster and nMDS). Based on the composition and abundance of phytoplankton, spatial variations were observed at a significant level (ANOSIM, R = 0.44, P < 0.01). Although the pairwise correlation analysis detected no significant effect of any single environmental variable on the abundance of C. geminatum, the multivariate analysis (BIO-ENV) between biotic and abiotic variables resulted in the best variables combination with all measured factors involved (temperature, salinity, turbidity, NO₃, NO₂, NH₄, PO₄ and SiO₃) which showed a combined effect during the bloom of C. geminatum in the Pearl River Estuary (ρ_w = 0.477).     

Extinction thresholds and negative responses of Afrotropical ant-following birds to forest cover loss in oil palm and agroforestry landscapes

Afrotropical ant-following birds are vulnerable to forest loss and disturbance, but critical habitat thresholds regarding their abundance and species richness in human-dominated landscapes, including industrial oil palm plantations, have never been assessed. We measured forest cover through Landsat imagery and recorded species richness and relative abundance of 20 ant-following birds in 48 plots of 1-km², covering three landscapes of Southwest Cameroon: Korup National Park, smallholder agroforestry areas (with farms embedded in forest), and an industrial oil palm plantation. We evaluated differences in encounter frequency and species richness among landscapes, and the presence of critical thresholds through enhanced adaptive regression through hinges. All species were detected in Korup National Park and the agroforestry landscape, which had similar forest cover (>85%). Only nine species were found in the oil palm plantation (forest cover = 10.3 ± 3.3%). At the 1-km² scale, the number of species and bird encounters were comparable in agroforests and the protected area: mean species richness ranged from 12.2 ± 0.6 in the park and 12.2 ± 0.6 in the agroforestry matrix to 1.0 ± 0.4 in the industrial oil palm plantation; whereas encounters decreased from 34.4 ± 3.2 to 26.1 ± 2.9 and 1.3 ± 0.4, respectively. Bird encounters decreased linearly with decreasing forest cover, down to an extinction threshold identified at 24% forest cover. Species richness declined linearly by ca. one species per 7.4% forest cover lost. We identified an extinction threshold at 52% forest cover for the most sensitive species (Criniger chloronotus, Dicrurus atripennis, and Neocossyphus poensis). Our results show that substantial proportions of forests are required to sustain complete ant-following bird assemblages in Afrotropical landscapes and confirm the high sensitivity of this bird guild to deforestation after industrial oil palm development. Securing both forest biodiversity and food production in an Afrotropical production landscape may be best attained through a combination of protected areas and wildlife-friendly agroforestry.     

Testing the effectiveness of surrogates for assessing biological diversity of arthropods in cereal agricultural landscapes

Agricultural intensification is altering biodiversity patterns worldwide. Rapid and effective methods are needed to monitor these changes in farmland biodiversity, but it becomes both a cost- and time-prohibitive task, particularly for hyper-diverse groups such as arthropods. We evaluated the effectiveness of surrogates in irrigated and rainfed wheat fields in a Mediterranean farmland in NW Spain in order to get a rapid tool to assess arthropod biodiversity. We studied six groups with different ecological needs (i.e. Aphididae, Aphidiinae, Coccinellidae, Formicidae, Heteroptera and Syrphidae) at species level (147 species), genus (105), family (10, only Heteroptera) and order (19) level. Higher taxa, cross-taxa and subset-taxa or total richness approaches were tested as well as the correlation in composition between levels for the selected groups, and the influence of farming regime. Genus richness was a good surrogate of species richness in all six groups studied (R² = 0.38–0.60), like family and order were for Heteroptera (R² = 0.37 and 0.29, respectively). Cross-taxa analyses showed that Aphididae and Aphidiinae genera (R² = 0.19 and 0.30, respectively) and species (R² = 0.20 and 0.28, respectively) were good surrogates for Aphidiinae and Aphididae species respectively. Coccinellidae genera (R² = 0.26) and species (R² = 0.25) were good surrogates for Heteroptera species. Finally, Aphididae and Coccinellidae both at genera (R² = 0.14 and 0.20, respectively) and at species levels (R² = 0.12–0.22, respectively) were good surrogates for total species richness of all groups. Genera composition was the best surrogate for the species composition within each group. Farming regime had no influence on the relationships between surrogates and species patterns in most cases. Our results suggest that genera level is a useful surrogate for all the studied groups and family is appropriate for Heteroptera. Genus level provided a saving of 15% of identification time in Aphididae and 80% for Coccinellidae. This proves its usefulness to asses and monitor biodiversity in wheat croplands and the possibility to reduce costs.