Temporal dynamics of aquatic communities and implications for pond conservation

Conservation through the protection of particular habitats is predicated on the assumption that the conservation value of those habitats is stable. We test this assumption for ponds by investigating temporal variation in macroinvertebrate and macrophyte communities over a 10-year period in northwest England. We surveyed 51 ponds in northern England in 1995/6 and again in 2006, identifying all macrophytes (167 species) and all macroinvertebrates (221 species, excluding Diptera) to species. The alpha-diversity, beta-diversity and conservation value of these ponds were compared between surveys. We find that invertebrate species richness increased from an average of 29.5 species to 39.8 species between surveys. Invertebrate gamma-diversity also increased between the two surveys from 181 species to 201 species. However, this increase in diversity was accompanied by a decrease in beta-diversity. Plant alpha-, beta- and gamma-diversity remained approximately constant between the two periods. However, increased proportions of grass species and a complete loss of charophytes suggests that the communities are undergoing succession. Conservation value was not correlated between sampling periods in either plants or invertebrates. This was confirmed by comparing ponds that had been disturbed with those that had no history of disturbance to demonstrate that levels of correlation between surveys were approximately equal in each group of ponds. This study has three important conservation implications: (i) a pond with high diversity or high conservation value may not remain that way and so it is unwise to base pond conservation measures upon protecting currently-speciose habitats; (ii) maximising pond gamma-diversity requires a combination of late and early succession ponds, especially for invertebrates; and (iii) invertebrate and plant communities in ponds may require different management strategies if succession occurs at varying rates in the two groups.     

An expert-based landscape permeability model for assessing the impact of agricultural management on amphibian migration

The persistence of pond-breeding amphibian populations is influenced on different spatial scales ranging from the individual breeding pond to surrounding habitat patches to landscape clusters of breeding pond populations. The connectivity among breeding ponds as well as the availability of suitable terrestrial habitats surrounding the ponds plays a major role in long-term viability of amphibian species. Besides road traffic and urban structures agricultural land activity can disrupt landscape connectivity through the use of pesticides, fertilizers and physical activity such as tillage. We developed an expert-based model to assess the impact of agricultural management measures on the migration area and terrestrial habitat availability for seven amphibian species. The model is based on a Habitat Suitability Index to identify suitable terrestrial habitats and includes a landscape permeability approach. Size of migration areas, connectivity of breeding ponds and number of reachable terrestrial habitats were modeled considering species-specific migration ranges and habitat preferences. We consider how pesticides application might lead to fragmentation and isolation of amphibian breeding pond populations. Therefore the potential disrupting impact of pesticides was simulated by inflating landscape resistance to medium and high migration cost. One amphibian species showed a decrease of migration area by 48.3% and a decrease of reachable terrestrial habitats by 41.5% at high migration costs. Three additional species showed a decrease of their migration areas between 31.5 and 35.7%. At increased migration cost, some of the investigated populations were isolated at breeding pond level or restricted to pond clusters. Our model could be used to prioritize conservation efforts for pond-breeding amphibians with adequate consideration of agricultural land use and its impact on amphibian migration.     

The colonization of ball-clay ponds by macroinvertebrates and macrophytes

SUMMARY. 1. The rate and nature of colonization of ball-clay ponds by aquatic macrophytes and macroinvertebrates were studied by comparing communities present in a scries of ten ponds of similar dimensions, but of different ages, ranging from 6 months to 15 years.
2. Multivariate analyses of the biotic data distinguished between'neutral'and'acid'ponds; further analyses concentrated on the former type.
3. Initial colonization of neutral ponds was rapid with a predictable sequence of species arrival, probably reflecting short dispersal distances. Variations in macroinvertebrate invasion times were related to dispersal strategy and ability. As the pond aged, successional changes, linked with macrophyte colonization, produced a shift in dominance from algivores and predators towards epiphyton grazers and detritivores. Some evidence of succession of species within invertebrate orders was found.
4. Low pH affected colonization principally by preventing the establishment of acid-intolerant immigrant species, but also by retarding succession.
5. It is concluded that non-interactive models of insular colonization, with constant immigration and extinction rates, are of limited applicability to pond colonization in temperate areas.     

Primary succession on lava domes on Terceira (Azores)

Questions: Are the vegetation attributes significantly different among lava domes and among geomorphologic units as a result of age and soil features? Are the successional rates equal in all the geomorphologic units of the domes? Are the colonizer species of lava domes totally replaced by other species in the late successional stages? Location: Terceira Island, Azores (Portugal). Methods: Three comparable domes of 240, 370 and 2080 yr old were selected. Data on floristic composition, vegetation bioarea (area occupied by plant species in transects), structure, demography and soil nutrients were collected. Quantitative and qualitative changes along the succession gradient were also analyzed. Results: Vegetation attributes were consistent with the successional stage of each dome in the primary sere; however, the geomorphologic units did not follow the same pattern. The influence of the rates of plant colonization and soil formation are responsible for the decrease of the successional rates from footslopes, to summits, to slopes. The vegetation successionally changes from Juniperus scrub, to Juniperus wood and forest, and there is little species replacement since the similarity in species composition is high between the 3 domes. Conclusions: This is a special type of direct succession that takes place mainly through an increase in biomass and structural complexity. We observed small wooded areas in the fissures of very young domes that are samples of later successional forests — a phenomenon that we call ‘zoom effect’.     

Phytoplankton succession and diversity in a warm monomictic,relatively shallow lake: Lake Volvi,Macedonia, Greece

In Lake Volvi, phytoplankton dominance was examined in relation to the main phases of the fluctuating physical state of the water column and nutrient levels. Four stages of algal succession were identified. The successional pattern was, in general, similar from year to year. External disturbances such as increased wind mixing and high floods had the effect of setting the succession back to an earlier stage.Nanoplanktic diatoms and flagellates dominated during the first stages of succession. The succession was running from r-selected species in early stages to K-strategists in summer and towards a mixed community in the terminal stage.Diversity was expressed by the indices of Gleason and Shannon (based on physical units and biomass). Interpretation of species diversity took into account the differential variations of its two components, the number of species and the evenness of their distribution. Diversity was more affected by evenness than by number of species.Diversity increased in late stages of succession corresponding to the complexity of the community (high number of species, high evenness). Physical disturbances influenced positively the diversity. The maximal diversity appeared in the transition periods between the compositional changes generated by disturbances and the true successional development. Disturbances may generate a more uniform distribution of diversity throughout the whole water column.The role of physical disturbances in increasing the phytoplankton diversity may be demonstrated from comparisons of diversity — evenness — species number of the same stages under different meteorological conditions.     

Does natural reforestation represent a potential threat to dung beetle diversity in the Alps?

Traditional agro-pastoral practices are in decline over much of the Alps, resulting in the complete elimination of livestock grazing in some areas. Natural reforestation following pastoral abandonment may represent a significant threat to alpine biodiversity, especially that associated with open habitats. This study presents the first assessment of the potential effects of natural reforestation on dung beetles by exploring the relationships between the beetle community (abundance, diversity, species turnover and assemblage structure) and the vegetation stages of ecological succession following pastoral abandonment. A hierarchical sampling design was used in the montane belt of the Sessera Valley (north-western Italian Alps). Dung beetles were sampled across 16 sampling sites set in four habitat types corresponding to four different successional stages (pasture, shrub, pioneer forest and beech forest) at two altitudinal levels. The two habitats at the extremes of the ecological succession, i.e. pasture and beech forest, had the greatest effect on the structure of local dung beetle assemblages. Overall, dung beetle abundance was greater in beech forest, whereas species richness, Shannon diversity and taxonomic diversity were significantly higher in pasture, hence suggesting this latter habitat can be considered as a key conservation habitat. Forests and pastures shared a lower number of species than the other pairs of habitats (i.e. species turnover between these two habitats was the highest). The two intermediate seral stages, i.e. shrub and pioneer forest, showed low dung beetle abundance and diversity values. Local dung beetle assemblages were also dependent on season and altitude; early-arriving species were typical of pastures of high elevation, whereas late-arriving species were typical of beech forests. It is likely that grazing in the Alps will continue to decrease in the future leading to replacement of open habitats by forest. This study suggests therefore that, at least in the montane belt, reforestation may have potentially profound and negative effects on dung beetle diversity. Maintaining traditional pastoral activities appears to be the most promising approach to preserve open habitats and adjacent beech forests, resulting in the conservation of species of both habitats.     

Fish species richness in spring‐fed ponds: effects of habitat size versus isolation in temporally variable environments

1. Species richness in a habitat patch is determined by immigration (regional) and extinction (local) processes, and understanding their relative importance is crucial for conservation of biodiversity. In this study, we applied the Island Biogeography concept to spring ponds connected to a river in southwestern Japan to examine how immigration and extinction processes interact to determine fish species richness in temporally variable environments. 2. Fish censuses were conducted 15 times in 13 study ponds at 1–4 month intervals from August 1998 through October 2000. Effects of habitat size (pond area), isolation (distance from the river) and temporal environmental variability (water level fluctuation) on (i) species richness, (ii) immigration and extinction rates and (iii) population size and persistence of each fish species were assessed. 3. The results revealed predominant effects of distance on species richness, immigration/extinction rates and population size and persistence. Species richness decreased with increasing distance but was not related to either pond area or water level fluctuation. A negative effect of distance on immigration rate was detected, while neither pond area nor water level fluctuation had significant effects on extinction rate. Further, population size and persistence of four species increased with decreasing distance, suggesting that, in ponds close to the river, immigrants from the river reduce the probability of extinction (i.e. provide a rescue effect), contributing to the maintenance of high species richness. 4. Overall results emphasise the importance of immigration processes, rather than extinction, in shaping patterns of species richness in our system. The predominant importance of immigration was probably because of (i) high temporal variability that negates habitat‐size effects and (ii) continuous immigration that easily compensates for local extinctions. Our results suggest that consideration of regional factors (e.g. connectivity, locations of source populations and barriers to colonisation) is crucial for conservation and restoration of local habitats.     

青海湖地区植被演变趋势的研究

青海湖地区作为祁连山系中段南麓的一个大型山间盆地,是一个独具特色的地区。这里的以草原为基带及其周围山地的高寒灌丛和高寒草甸垂直系列,有其自身的特点和发展趋势。随着整个青藏高原的强烈隆升,本区植被也具有一系列的明显变化。大片森林趋于消退,仅残存有少数适应高寒生境的树种;温性植被类型局限于海拔较低处,而高寒植被类型相对分布较广。分析表明,青海湖地区的整体植被景观有向寒旱生境方向发展的演变趋势。本区植被出现上述演变趋势的主要原因在于该地区生境因抬升而趋于寒旱的过程中,植物种对其生境变化表现出不同的忍耐性和适应性所致。     

长白山针阔混交林不同演替阶段的昆虫多样性

昆虫多样性变化对生态系统健康有重要的指示作用, 为研究昆虫群落变化与生境演替之间的关系, 本研究采用网捕、灯诱和诱捕法系统调查了长白山针阔混交林不同演替阶段（次生白桦林、次生针阔混交林、原始阔叶红松林）昆虫群落的组成和多样性, 分析了昆虫在森林演替过程中的规律及与植被群落之间的关系。系统调查共采集昆虫标本8 183头, 隶属于14个目699种, 其中鳞翅目和鞘翅目是主要优势类群。次生针阔混交林昆虫的个体数量最多, 原始阔叶红松林中物种数最多。不同演替阶段昆虫群落的物种数和个体数差异不显著, 但次生针阔混交林、原始阔叶红松林的Fisher’s α指数显著高于次生白桦林。目水平上的昆虫多样性未表现出显著性差异. 昆虫多样性在森林演替过程中和草本植物多样性的变化趋势相同;由于食性和生境选择的不同, 森林演替过程中鳞翅目昆虫多样性逐渐升高, 而鞘翅目多样性逐渐降低。     

Vegetation fluctuation in mediterranean dune ponds in relation to rainfall variation and water extraction

Abstract. The structure of dune ponds hygrophytic vegetation has a spatial organisation in belts around the pond basin, closely related to water level and flooding regime. Doñana National Park has an important representation of temporal dune ponds, which are subjected to rainfall fluctuations and may be suffering the impact of water extraction from the neighbouring tourist resort. Permanent transects in a vegetation complex of five dune ponds have been monitored during a eight year period (1990-1997). This period was characterised by a number of dry years (annual rainfall around 300 mm), located between two wet cycles (800-900 mm). Transects were analysed in 1990 (wet period), 1994 (dry) and 1997 (wet) by hierarchical agglomera-tive clustering. During the dry period hygrophytic species showed regression, with a high mortality of some species like Ulex minor, while the xerophytic species advanced to lower areas. Seedlings of some xerophytic species colonised the dry surface of the pond basin. The lowering of the water table varied in the different ponds, ranging from 312 to 190 cm depending on topography and the distance to the pumping area. The new period of flooding during 1995-96 and 1996-97 cycles provided the opportunity for hygrophytic spe cies to re-establish themselves in their original places. This study suggest that changes in vegetation are caused by the interaction between weather conditions and human disturbance (water extractions). In our example man-made disturbance is more marked during the dry periods while wet periods tend to obscure the effects of water extractions. From a management perspective, long-term monitoring of water table and vegetation structure is revealed as a key procedure to the management of land-water ecotones on pressured areas and threatened habitats.     

The role of environmental factors in the composition of anuran species in several ponds under the influence of coal mining in southern Brazil

Environmental pollution caused by the disposal of chemicals or toxins into the environment represent a great threat to amphibians. In this study, it was evaluated which environmental factors of ponds under the influence of coal-mining influence the composition of anuran species. For this purpose, anuran samples were performed in ponds in coal extraction areas in southern Brazil. Physical and chemical characteristics of water, sediment and structural characteristics of the ponds were determined. The content of copper in the sediments of the ponds was the main variable to explain the composition of pond species. Besides copper, it is evident the relevance of number of vegetation strata at pond border and pond area on the composition of anurans. It is shown that the composition of species in ponds under the influence of mineral coal mining activity may be a result of historical perturbations, remaining only the most tolerant towards colonization. From the results obtained in this work it can be suggested that there is a synergistic interaction between environmental factors and the coal mining effects on the anurans fauna of impacted ponds. Thus, efforts should be directed to elucidate the effects of pollutants exposure levels on the species, the understanding of sub-lethal and lethal effects of each pollutant on each species, as well as how local populations can be maintained through recruiting rates of larvae and anurans of the impacted ponds.     

Secondary succession and breeding bird community structure: Patterns of resource utilization

Summary Structure of breeding bird communities was compared among four habitat types representative of stages present in most old-field successions in the eastern deciduous forest formation of North America. The successional catagories, defined by vegetational structure, were designated herbaceous (type A habitats) herb, shrub and sapling (type B), young forest (type C), and older forest (type D). Density of breeding birds was lowest in A habitats, rose sharply in B habitats and reached a maximum in D habitats. Species richness and number of feeding guild showed similar patterns. Mean number of species per guilds was highest in D habitats. Generalist feeding guilds were predominant in type A and B habitats, primarily due to the importance of the graminivore-insectivore guild. Specialist guilds increased in importance with succession due to addition of several insectivorous guilds in later successional stages. Patterns of occurrence of individual feeding guilds are analyzed and discussed with respect to changes in vegetational structure. Variance in community structure was generally highest in A habitats and lowest in D habitats; this is discussed in relation to the evolution of saturated, coadapted communities.     

Structure and succession of ant assemblages in a north European sand dune area

Ant assemblages of a successional dune area (Tvärminne, south Finland) were analysed at three levels: the distribution of species among habitats, the distribution of colonies within habitats and the spatio-temporal distribution of individuals. The distribution of ant species among habitat patches representing different stages of succession is correlated with the composition of the epigeic fauna, the number and condition of dead twigs on the ground and the vegetation architecture. The composition of ant assemblages seems relatively independent of the plant species composition, and there are uncoordinated successional steps between the vegetation and ant communities.
In the early successional stages interference competition is weak and insignificant, as indicated by the random spatial arrangement of colonies, the absence of postcompetitive niche segregation and the low encounter rates of ant workers on the ground and at baits. In the aggressive behavioural hierarchy, Formica cinerea is a submissive species as compared with either Formica sanguinea or Lasius alienus.     

Determinant landscape‐scale factors on pond odonate assemblages

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Soil chemical properties as related to forest succession in a highland area in north-east Tasmania

The relationship between vegetational type and a number of soil chemical factors was examined in secondary successions from fire-maintained eucalypt/grass to climax rainforest communities growing on uniform granitic soil parent material. Canonical variates analysis, which utilized the following variables: pH; loss on ignition; total N, P, K, Ca, and Mg; cation exchange capacity and exchangeable Ca, K, and Mg; and potentially mineralizable N, revealed close overall similarity between surface soils of adjacent types, and significant differences among those of types distant from each other in the successional sequences. Exchangeable Ca, mineralizable N, total N. P, and Mg, and pH all differed significantly among soils of the vegetational types. However, the only identifiable gradients in soil properties that were detected within a successional sequence were in total and mineralizable N, which tended to increase, and pH, which generally tended to decrease with progression towards the climax vegetation. Nitrification was promoted by the presence of Acacia dealbata and apparently inhibited by the presence of Leptospermum lanigerum; it was more rapid in soils beneath late successional vegetation than in those from climax vegetation or early stages of succession, and was inhibited in soil from old (> 200 years) grassland. It was concluded that differences among soils in chemical composition and rates of mineralization of N were due to differences in species composition of the vegetational types that they carried for the time being.     

A comparative study of phenotypic traits related to resource utilization in anuran communities

Larval anuran communities vary along a gradient of pond permanency. The families Hylidae, Ranidae, and Bufonidae have each diversified into multiple pond types. Species using ponds that dry seasonally (vernal ponds) must compete well to metamorphose before pond drying, while permanent ponds, which contain more predators, produce weaker selection for competitive ability. Quantifying phenotypic traits related to resource acquisition in 14 anuran species provides insight into the mechanistic underpinnings of adaptive radiation in anuran lineages. Under controlled laboratory conditions and at both early and late developmental stages, relative growth rate, relative consumption rate, assimilation efficiency and production efficiency varied significantly among species. As predicted, vernal pond species had high growth rates relative to species using more than one pond type. However, within a pond type, families frequently differed in phenotype. In species using permanent ponds with fish predators, hylids had high growth rates while ranids had low growth rates, and in species using vernal ponds, bufonids had higher assimilation efficiencies than hylids. Differences also occurred between stages; hylids and ranids in permanent, but fishless, ponds were similar at an early stage, but late stage hylids in the same pond type had lower growth and consumption rates, and higher assimilation efficiencies than ranids. Functional relationships between phenotypic traits also differed among species and developmental stage. Negative correlations between evolutionary change (independent contrast values) in both mass and growth rate (both stages), and mass and consumption rate (late stage), suggest the presence of trade-offs. These results indicate that different lineages have diversified in different ways into the same pond types.     

Lowland boreal forests characterization in Algonquin Provincial Park relative to beaver (Castor canadensis) foraging and edaphic factors

Beaver (Caster canadensis) foraging and edaphic conditions can modify the vegetational characteristics of woody plant community in lowland boreal forests. Effective management of these areas requires an understanding of the relative contribution of these factors in shaping the woody plant community structure. Our objective was to quantify the effects of herbivory by beavers and edaphic conditions on woody plant community organization of lowland boreal forests surrounding beaver ponds. Woody vegetation and soils were sampled at 15 ponds occupied by beavers and one other pond abandoned by them in southern Algonquin Park, Ontario. We measured spatial variation in plant diversity, foraging rates and sapling recruitment of trees and shrubs along gradients of beaver foraging intensity and soil moisture, P, K, Mg, and pH. Beavers fed preferentially on a small number of deciduous species and the number of cut stems declined sharply with increasing distance from ponds. Conifers increased in relative dominance to deciduous species in the presence of beavers. Plant species richness and stem and basal area diversity peaked at intermediate distances (about 25 m) from ponds. Sapling recruitment by non-preferred species was positively related to foraging intensity. Total stem abundance and basal area and sapling recruitment by four preferred species (Populus tremuloides, Acer rubrum, Acer saccharum and Corylus cornuta) were negatively related to foraging intensity. However, by including Alnus rugosa and Salix bebbiana (also preferred by beavers) these patterns changed, becoming positively related to foraging intensity. There was also a pronounced gradient in soil moisture, which also decreased with distance from ponds. The other measured edaphic variables did not vary consistently with distance from ponds. Sapling recruitment in mesic versus xeric species varied consistently with hydrid conditions along the moisture gradient, such that variation in moisture also could produce the observed pattern of plant diversity. Diversity patterns changed three years after beaver abandonment of a pond, though sapling recruitment patterns in preferred and non-preferred species around the abandoned pond were similar to the occupied ponds. These observations suggest spatial variation in woody plant richness and diversity could be determined by combined effects of both herbivory (disturbance by beavers) and variable responses of different species to edaphic conditions.     

Secondary succession, soil formation and development of a diverse community of oribatids and saprophagous soil macro-invertebrates

Investigations into different stages of secondary succession (from a wheat field to a beechwood on Threstone; Northern Germany) demonstrated the formation of a carbon rich top soil in later successional stages. Parallel to changes in plant species and soil formation, there were also changes in species composition and diversity of saprophagous macro-invertebrates (Lumbricidae, Diplopoda, Isopoda) and oribatid mites (Acari: Oribatida). Diversity of diplopod and isopod species increased after cessation of cultivation, but in a late successional stage (ca 50 y-old fallow, ash-dominated wood) species number of diplopods and isopods declined strongly. In comparison with the other soil invertebrate groups, species composition of earthworms among the sites was more similar. Accumulation of soil C was assumed to be related to wood formation and occurrence of woody debris and recalcitrant leaf litter of beech trees. Incorporation of recalcitrant litter materials by earthworm species living in the upper mineral soil presumably contributed significantly to accumulation of soil C. Accumulation of soil C was accompanied by the development of an oribatid mite community rich in species. In early successional stages oribatids predominantly colonized the litter layer, while most oribatid mites of the beechwood inhabited the upper mineral soil. Maximum diversity of oribatid mites in the beechwood is assumed to be related to instability of the mineral soil caused by earthworm activity. Changes in species composition and diversity are discussed considering succession theory. Even soil invertebrates of similar trophic groups appear to respond very differently to successional changes. It is concluded that conservation strategies to maintain high diversity of soil invertebrates are most likely to be successful if a wide range of habitats of different successional stages is included.     

Diversity of surface dwelling beetle assemblages in open-cast lignite mines in Central Germany

We investigated species richness of ground dwelling beetle assemblages in two non-reclaimed lignite mines and a dump in Central Germany by means of pitfall trapping. During a period of five months, a total of 203 beetle species within 27 families represented by 4099 individuals were trapped. This included 75 species of ground beetles represented in a sample of 957 individuals from which 10 species are regionally endangered. The number of individuals, species richness, as well as the proportions of endangered species did not differ between successional stages whereas species composition of sites could be related well to a set of environmental variables. High values of beta-diversity between sites indicated that the total number of species recorded is caused by habitat diversity. From the viewpoint of nature conservation, we conclude that postmining areas can play a key role in conservation of beetle diversity in agricultural areas since they harbour threatened species whose original habitats are now rare due to human impact. An important task for future management of postmining areas is to maintain successional processes and to prevent loss of habitat diversity through afforestation. Areas with extreme soil conditions should also be preserved for long-term availability of bare soil and pioneer vegetation and associated fauna.