Seed dispersal by changing frugivore assemblages: a mechanistic test of global change effects

In the face of global change it is important to understand how changes in species abundance and richness can affect ecosystem functions. Here we modelled seed dispersal by animals in a fragmented secondary forest of the Cantabrian Range (northwestern Iberian Peninsula), simulating the activity of six frugivorous bird species when dispersing three species of fleshy‐fruited trees. We calculated the density and richness of seeds deposited across a forested landscape, as well as the density of seeds arriving to open areas. We 1) study the complementarity of functional traits of each species with frugivore assemblages varying in species compositions (i.e. abundance and richness of bird assemblages), 2) identify those bird species whose functional roles are not redundant, and 3) explore the response of seed dispersal to random losses and to two non‐random bird loss scenarios (i.e. overhunting and fewer individuals from migrant species). We found that simulations with the avian composition observed in the field (i.e. with uneven abundances of six bird species) led to values of seed dispersal higher to those emerging from four bird species equally abundant. The selective removal of dominant bird species led to significant decays in seed dispersal, suggesting non‐redundant roles of abundant bird species. Seed dispersal decays were stronger under non‐random than random scenarios of bird loss. In terms of seed density, the functional decays also differed between the scenarios of overhunting and reduced arrival of migrant birds, notably beyond 50% changes in bird species composition. Our results illustrate the need to integrate species composition (controlling for bird abundance and richness) and their sensitivity to disturbances when predicting the impact of global change on ecosystem functions.     

广东鹤山丘陵人工林林下鸟群落研究

2003年5月到2004年4月,在鹤山人工林中张网6353网小时,捕到林下鸟28种110只,平均网捕率为1.73只/100网h。其中冬候鸟的种类和数量分别占整个网捕鸟种类和数量的42.86%和33.64%。优势种是大山雀(P arusm ajor)、白头鹎(Py cnonotus sinensis)和红胁蓝尾鸲(T arsig er cyanurus)。鹤山20a林龄的人工林林下鸟群落具有:种类和数量贫乏、网捕率低、画眉科的鸟少等特点。林下鸟群落的种类、数量、组成和网捕率与植被有关,相思林种类最丰富、网捕率最高;针叶林种类最少、网捕率最低;4种植被类型中林下鸟种类和网捕率大小排序是:相思林>荷木林>桉树林>针叶林。相思林与荷木林有最大的种的相似性(0.43)、而相思林与针叶林种的相似性最小(0.20)。林下鸟丰度和网捕率均存在季节变化,冬季种类最丰富、春季次之、而夏季和秋季种类最少。在针叶林(F3,44=4.514,p<0.01)和荷木林中(F3,44=4.449,p<0.01),林下鸟的网捕率有极显著的季节变化,冬季的网捕率最高、夏季的网捕率最低;而在相思林(F3,44=1.893,p>0.05)和桉树林中(F3,44=1.212,p>0.05),林下鸟的网捕率季节差异不显著。     

Birds in Anthropogenic Landscapes: The Responses of Ecological Groups to Forest Loss in the Brazilian Atlantic Forest

Habitat loss is the dominant threat to biodiversity and ecosystem functioning in terrestrial environments. In this study, we used an a priori classification of bird species based on their dependence on native forest habitats (forest-specialist and habitat generalists) and specific food resources (frugivores and insectivores) to evaluate their responses to forest cover reduction in landscapes in the Brazilian Atlantic Forest. From the patch-landscapes approach, we delimited 40 forest sites, and quantified the percentage of native forest within a 2 km radius around the center of each site (from 6 - 85%). At each site, we sampled birds using the point-count method. We used a null model, a generalized linear model and a four-parameter logistic model to evaluate the relationship between richness and abundance of the bird groups and the native forest amount. A piecewise model was then used to determine the threshold value for bird groups that showed nonlinear responses. The richness and abundance of the bird community as a whole were not affected by changes in forest cover in this region. However, a decrease in forest cover had a negative effect on diversity of forest-specialist, frugivorous and insectivorous birds, and a positive effect on generalist birds. The species richness and abundance of all ecological groups were nonlinearly related to forest reduction and showed similar threshold values, i.e., there were abrupt changes in individuals and species numbers when forest amount was less than approximately 50%. Forest sites within landscapes with forest cover that was less than 50% contained a different bird species composition than more extensively forested sites and had fewer forest-specialist species and higher beta-diversity. Our study demonstrated the pervasive effect of forest reduction on bird communities in one of the most important hotspots for bird conservation and shows that many vulnerable species require extensive forest cover to persist.     

广西猫儿山地区鸟类组成及垂直分布格局

猫儿山是华南地区的最高峰,为了了解其鸟类随着海拔高度变化的规律,利用网捕法和样线法对猫儿山地区的鸟类组成及分布格局进行了研究。结果表明,猫儿山地区共有鸟类268种,隶属于16目51科,其中留鸟130种,夏候鸟51种,冬候鸟15种,旅鸟72种。依据不同海拔的典型植被类型把猫儿山地区分成7类生境,其中低海拔的农田生境鸟类多样性最丰富,有156种。随着海拔的升高,猫儿山鸟类种数逐渐减少,G-F指数也表现相似的规律。猫儿山鸟类在区系组成上主要以东洋界鸟类为主,在181种繁殖鸟中,东洋界鸟类有149种,古北界鸟类有15种,其余为广布种。随着海拔的升高,东洋界的鸟类所占的比例逐渐降低,而古北界的鸟类所占的比例逐渐升高。猫儿山鸟类组成的垂直分布格局的形成是多种因素共同作用的结果。     

Dragonfly species richness on man-made ponds: effects of pond size and pond age on newly established assemblages

We studied the abundance and species richness of adult dragonflies in 11 artificial ponds which were recently established (within 2years). We found that the adult dragonfly assemblage patterns were influenced by pond size as well as pond age. The species richness was positively correlated with the pond size, which was because the distributional patterns of species were significantly nested according to pond area. The species richness was highly correlated with pond age in association with the vegetation cover within ponds. It was suggested that the species richness was enhanced by the increasing immigration rate of species which favor well-vegetated ponds.     

Changes in trophic state and aquatic communities in high Arctic ponds in response to increasing goose populations

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Avifauna associated with ephemeral ponds on the Cumberland Plateau, Tennessee

ABSTRACT.   Although ephemeral ponds act as small hotspots of plant, invertebrate, and salamander diversity, the importance of such ponds for birds has been little studied. We hypothesized that ephemeral ponds on the Cumberland Plateau in Tennessee would support a greater abundance, richness, and diversity of birds than the surrounding hardwood forests. In 2004, we recorded all birds seen or heard in 10 min within 50-m radius circles at 25 ephemeral ponds. We repeated the counts at control sites located 150 m from each pond in the surrounding forest. To quantify potential food availability, we captured aerial invertebrates using sweep nets at four points around a subsample of eight ephemeral ponds and at an equal number of control sites. We found significantly greater bird abundance, richness, and species diversity at ephemeral ponds than at control sites, and that pond area was not associated with either bird abundance or richness. Bird community composition at pond and control sites was similar. Aerial invertebrates were significantly more abundant at ephemeral ponds than at adjacent forest sites, providing one possible explanation for greater bird abundance at ephemeral ponds.     

Ciliate populations in temporary freshwater ponds: seasonal dynamics and influential factors

SUMMARY 1. The ciliate populations of two temporary ponds in southern Ontario were studied throughout their aquatic phases in 2001. Pond I (～1 ha) held water for 98 days, whereas Pond II (～0.25 ha) held water for 34 days. Populations were assessed both within the ponds themselves and within a series of enclosures in which invertebrate predator pressure was manipulated. 2. In the natural pond water, total ciliate abundance in Pond II rose rapidly from day 1 increasing two orders of magnitude by day 7. In contrast, total abundance in Pond I began at the same level as in Pond II but increased much more slowly, reached a plateau of around 500 individuals L^?1, and increased again late in the hydroperiod. 3. Despite being only 500 m apart, the two ponds were fairly dissimilar in terms of their species richness and species composition. Pond I contained 50 species compared with 70 species for Pond II, with only 24 species shared. Additional species occurred within the enclosures raising the total species richness to 145 species; 88 from Pond I, 104 from Pond II, with 47 species (30%) in common. Pond II contained more mid‐sized ciliates (50–200 μm), whereas Pond I was dominated by smaller ciliates, especially in mid‐May and early June. In Pond I, cumulative species richness throughout the hydroperiod was highest in the predator addition enclosures (65 ± 4 species), followed by the partial‐predator exclusion enclosures (50 ± 4). Lowest species richness was found in the control enclosures (39 ± 2) and in the pondwater controls (39 ± 0). Differences between the ciliates in the natural pond water and the enclosures appeared to be related to a greater concentration of phytoplankton within the enclosures (perhaps resulting from extensive growth of duckweed, Lemna, outside), and higher densities of zooplankters in the pond. 4. The physicochemical environment influenced species richness, total abundance and the number of rare species (27 in Pond II versus 13 in Pond I). Variation in ciliate abundance in Pond I could be explained by the number of days after filling (39%) and enclosure treatment (23%). These two parameters also explained 72% of the variation in species richness in Pond I (46 and 26%, respectively). Sixty‐five per cent of the variation in abundance in Pond II could be explained by the measured parameters: number of days after filling 27%, pH 19%, and nitrate levels 12%. Fifty‐two per cent of the variation in species richness was explained by the environmental parameters, of which pH was the most influential. Species succession was a strong feature of both ponds and its relationship to environmental variables and the presence of other organisms is discussed. 5. Addition of invertebrate predators resulted in higher abundance and higher species richness for a limited time period in one of the ponds – suggesting that differences in foodweb dynamics may influence ciliate community composition.     

Apparent global ubiquity of species in the protist genus Paraphysomonas

Evidence is presented for the ubiquity of protist species. Using the example of protists that leave traces (siliceous scales) of their recent population growth, we show that most - perhaps all species in the genus Paraphysomonas, are ubiquitous. Of the species recorded in surveys carried out worldwide, we have identified 78% of their number in 0.1 cm2 of sediment collected from a freshwater pond (total area 10(8) cm2) in England. Moreover, the pond appears to act like a microcosm of aquatic environments in general, for species that are globally rare or abundant, are likewise rare or abundant in the pond. We assume that the rate of neutral migration to the pond is greatest for the globally abundant species. As these species are probably capable of growth in a broad range of conditions, they will more frequently encounter the environment they require for population growth. Thus globally abundant species are also locally abundant in the pond - a pattern that will be amplified by periodic cyst production. Ubiquitous dispersal is probably driven by very high absolute abundance of individuals, and the water column of the pond was estimated to support >10(14) Paraphysomonas individuals. Ubiquity will dampen rates of speciation, and the evidence presented here indicates that global species richness of Paraphysomonas is indeed modest - perhaps close to what is already known.     

Aquatic insects decline in abundance and occupy low‐quality artificial habitats to survive hydrological droughts

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Significant decrease in local butterfly community during the last 15 years in a calcareous hill of the middle Korea

Recently the significant decreases of species richness and abundance among terrestrial animals including butterflies are reported due to habitat change, overexploitation, and global warming. We compared the butterfly species composition and abundance from 1999 and 2014–2015 in a calcareous hill site of the middle part of Korea using a line transect method. There was a significant decrease in the number of individuals (abundance) and the number of species (richness) from 1999 to 2014–2015. This decrease was more prevalent among northern species than southern species, and the local extinct species were more prevalent among northern species, showing the influence of global warming on butterfly assemblages. However, no impact of habitat change was observed because of maintenance of the grasslands, which is caused by the dry soils of the calcareous region.     

Effects of an artificial and annual opening of a natural sandbar on the fish community in a coastal lagoon system: a case study in Lagoa do Peixe floodplains,southern Brazil

Two hypotheses were tested: that the artificial sandbar opening decreases the richness, diversity and abundance of fishes and alters the fish composition in floodplain ponds; that the salinity variations influence fish richness, diversity, abundance, as well as composition. Results suggest that artificial sandbar openings did not reduce the richness or diversity of freshwater fishes in southern Brazil floodplain ponds. Nevertheless, this process causes an increase in salinity, which determines significant differences in species composition between natural and managed areas. In this sense, the artificial sandbar opening must be considered with caution, since the area of study is one of the most important conservation units in wetland systems of southern Brazil.     

Perennial Agroenergy Feedstocks as En Route Habitat for Spring Migratory Birds

Increased production of bioenergy crops in North America is projected to exacerbate already heavy demands upon existing agricultural landscapes with potential to impact biodiversity negatively. Grassland specialist birds are an imperilled avifauna for which perennial-based, next-generation agroenergy feedstocks may provide suitable habitat. We take a multi-scaled spatial approach to evaluate the ability of two candidate second-generation agroenergy feedstocks (switchgrass, Panicum virgatum, and mixed grass–forb plantings) to act as spring migratory stopover habitat for birds. In total, we detected 35 bird species in mixed grass–forb plantings and switchgrass plantings, including grassland specialists and species of state and national conservation concern (e.g., Henslow’s Sparrow, Ammodramus henslowii). Some evidence indicated that patches with higher arthropod food availability attracted a greater diversity of migrant bird species, but species richness, total bird abundance, and the abundance of grassland specialist species were similar in fields planted with either feedstock. Species richness per unit area (species density) was relatively higher in switchgrass fields. The percent land cover of forest in landscapes surrounding study fields was negatively associated with bird species richness and species density. Habitat patch size and within-patch vegetation structure were unimportant in predicting the diversity or abundance of spring en route bird assemblages. Our results demonstrate that both switchgrass and mixed grass–forb plantings can attract diverse assemblages of migrant birds. As such, industrialized production of these feedstocks as agroenergy crops has the potential to provide a source of en route habitat for birds, particularly where fields are located in relatively unforested landscapes. Because industrialization of cellulosic biomass production will favor as yet unknown harvest and management regimes, predicting the ultimate value of perennial-based biomass plantings for spring migrants remains difficult.     

Determinants of species‐area relationships for marsh‐nesting birds

ABSTRACT To clarify the underlying causes of the species‐area relationship in marsh‐nesting birds, I studied eight freshwater tidal marshes of the Connecticut River that differed in area, degree of isolation, mudflat cover, water cover, tidal regime, and extent of individual plant communities. I measured these habitat variables on aerial infrared photos, and surveyed bird populations by mapping the distribution of all birds in marshes under 5 ha in area and establishing 50‐m radius plots in marshes over 5 ha. From surveys, I determined species richness, population densities, and total populations. Analysis revealed a positive relationship between species richness and area, but no correlation between area and habitat heterogeneity. Other habitat variables were poor predictors of species richness. The lack of a relationship between habitat and species richness appeared to be a consequence of most vegetation types present not being sufficiently distinct for birds to differentially associate with them. I also found no relationship between bird population density and area, suggesting that habitat quality in marshes did not improve with increasing size, and species evenness declined with increasing richness because greater richness was associated with the presence of more rare species. Larger marshes had more rare species, species with larger populations, and species with a minimum threshold area for occurrence. Thus, my results are consistent with theoretical predictions that larger populations are less prone to local extinction and, as individuals are added to a community, more rare species are present.     

Patterns in benthic food webs: a role for omnivorous crayfish?

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty-one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment-dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte-associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.     

The Influence of Dry-season Conditions on the Bottom Dwelling Fauna of an East Australian Sub-tropical Estuary

Spatial patterns in benthic infaunal community structure of Port Curtis estuary (north-eastern Australia) were determined from quantitative grab samples and examined in relation to environmental variables. A total of 149 riverine, estuarine and open coastal stations were sampled during the winter survey, and 5744 individuals from 466 species identified. Filter-feeding organisms (primarily polychaetes, molluscs and crustaceans) dominated the benthos, and accounted for 50% of the total species abundance and 30% of the total species richness. Most taxa were uncommon, and 98% of species individually represented less than 2% of the total abundance. Distributional patterns in total species richness and abundance were highly correlated, and both parameters varied significantly with sediment grain size. Numbers of species and individuals were typically highest in coarse-sand and gravel sediments, and were lowest in fine, well-sorted, sands. Cluster analysis of species abundance data revealed nine community groupings characterised by small species sub-sets with restricted distributions. These groupings were primarily related to sediment grain size, sediment organic carbon content, salinity and depth. Not all variation in community structure was explained by these environmental variables, and it is likely that other unmeasured factors play an important role in determining benthic faunal composition in the estuary.     

Determinant landscape‐scale factors on pond odonate assemblages

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How Does Environmental Variation Affect the Distribution of Dragonfly Larvae (Odonata) in the Amazon-Cerrado Transition Zone in Central Brazil?

This study investigated the effects of environmental variation on assemblages of dragonfly larvae (Odonata). We hypothesize that there is a significant correlation between species richness, species composition, and abundance of Odonata individuals, and habitat integrity and abiotic variables. To test this hypothesis, we sampled odonate larvae at 12 streams in the Suiá-Miçú River basin in Mato Grosso, Brazil, during three different periods of the year. Local physical and chemical variables (temperature, pH, turbidity, electrical conductivity (EC), dissolved oxygen (DO), total dissolved solids (TDS), and oxidation reduction potential (ORP)) were measured at each site using a multi-parameter probe, and integrity was assessed using the Habitat Integrity Index (HII). The variation in richness, abundance, and composition of Odonata species was related to the environmental variables analyzed, primarily by the abiotic factors pH, electrical conductivity, dissolved oxygen, total dissolved solids, and oxidation reduction potential. Our hypothesis was corroborated for the suborder Anisoptera, which showed a significant relationship with these variables, whereas Zygoptera was only related to pH. Our results show the importance of physical and chemical conditions in ecological studies using Odonata larvae as tools for the management and conservation of freshwater ecosystems.     

Effects of intensive rice production practices on avian biodiversity in Southeast Asian managed wetlands

Rice fields are common throughout the agricultural landscape of Southeast Asia and sustain various bird species. These birds can provide ecosystem services, such as pest control, that improve agricultural yields whilst minimising the use of agrochemicals. This study quantified avian biodiversity in rice production landscapes during three farming stages in Peninsular Malaysia. In Malaysia, rice fields can be an important habitat for migrating birds due to Malaysia’s position on the East-Asian–Australasian Flyway. We determined bird abundance, species richness, and composition in rice field landscapes and compared these during different stages of rice growing. Wetland and terrestrial birds were counted in rice fields using the point-count method. Sixty sampling points were randomly established in three locations, from which 3447 individual birds of 46 species and 26 families were recorded. There was a significant difference in total bird abundance and species richness between the three different stages of rice growing. The growing stage supported greater bird abundance and species richness compared to the pre-harvest and post-harvest stages. Rice-growing provides temporary habitats to different bird species in this managed aquatic landscape. This implies the presence of abundant food, such as small fish and amphibians. The evidence from this study suggests that biodiversity-friendly agricultural practices should be implemented to improve habitat quality for birds in rice production landscapes.