Maintenance Of Species Richness Research Articles

Controlling the abundance of a native invasive plant does not affect species richness or functional diversity of wet grasslands

AbstractAimIn this study, we tested plant community‐based management methods to reduce the abundance of the invasive native plant Jacobaea aquatica (marsh ragwort). As J. aquatica mainly occurs in species‐rich wet grasslands, our aim was to define management measures that do not reduce the conservation value of the resident communities.LocationData were collected from 20 independent sites which varied in productivity and management intensity across the pre‐alpine Allgäu region (South Germany).MethodsWe monitored effects of temporary abandonment and decreased mowing intensity in very low‐ and low‐productive sites, as well as of decreased mowing and fertilization at moderately productive sites. Abundances of J. aquatica and the co‐occurring species were recorded at start and end of two experiments (2018–2021: very low‐ and low‐productive conservation grasslands; 2017–2020: moderately productive agricultural grasslands), while functional traits data of all species were gathered from the literature and specific databases. Generalized linear mixed‐effects models (GLMMs) were used to analyse the effects of management intensity on the abundance of J. aquatica, functional diversity and species richness of the resident communities.ResultsAt all productivity levels, the abundance of J. aquatica declined under reduced management. Changes in community composition and species richness of the resident community were less pronounced than the reduction of J. aquatica, but species richness declined under lowest management intensities. Thus, moderate reduction in management intensity provided the most benefits in terms of reduction of J. aquatica, and maintenance of species richness and composition of the resident plant community.ConclusionsReducing management intensity in wet grasslands decreases the abundance of J. aquatica and thus is a suitable method to control this species. As plant community responses were only partially consistent, management plans must account for the productivity of invaded sites. To avoid negative effects on grassland biodiversity, only moderate suppression of J. aquatica is recommended.

Demographic consequences of heterogeneity in conspecific density dependence among mast-fruiting tropical trees.

The role of conspecific density dependence (CDD) in the maintenance of species richness is a central focus of tropical forest ecology. However, tests of CDD often ignore the integrated effects of CDD over multiple life stages and their long-term impacts on population demography. We combined a 10-year time series of seed production, seedling recruitment and sapling and tree demography of three dominant Southeast Asian tree species that adopt a mast-fruiting phenology. We used these data to construct individual-based models that examine the effects of CDD on population growth rates (λ) across life-history stages. Recruitment was driven by positive CDD for all species, supporting the predator satiation hypothesis, while negative CDD affected seedling and sapling growth of two species, significantly reducing λ. This negative CDD on juvenile growth overshadowed the positive CDD of recruitment, suggesting the cumulative effects of CDD during seedling and sapling development has greater importance than the positive CDD during infrequent masting events. Overall, CDD varied among positive, neutral and negative effects across life-history stages for all species, suggesting that assessments of CDD on transitions between just two stages (e.g. seeds seedlings or juveniles mature trees) probably misrepresent the importance of CDD on population growth and stability.

Do Dominant Ants Affect Secondary Productivity, Behavior and Diversity in a Guild of Woodland Ants?

The degree to which competition by dominant species shapes ecological communities remains a largely unresolved debate. In ants, unimodal dominance–richness relationships are common and suggest that dominant species, when very abundant, competitively exclude non-dominant species. However, few studies have investigated the underlying mechanisms by which dominant ants might affect coexistence and the maintenance of species richness. In this study, we first examined the relationship between the richness of non-dominant ant species and the abundance of a dominant ant species, Formica subsericea, among forest ant assemblages in the eastern US. This relationship was hump-shaped or not significant depending on the inclusion or exclusion of an influential observation. Moreover, we found only limited evidence that F. subsericea negatively affects the productivity or behavior of non-dominant ant species. For example, at the colony-level, the size and productivity of colonies of non-dominant ant species were not different when they were in close proximity to dominant ant nests than when they were away and, in fact, was associated with increased productivity in one species. Additionally, the number of foraging workers of only one non-dominant ant species was lower at food sources near than far from dominant F. subsericea nests, while the number of foragers of other species was not negatively affected. However, foraging activity of the non-dominant ant species was greater at night when F. subsericea was inactive, suggesting a potential mechanism by which some non-dominant species avoid interactions with competitively superior species. Gaining a mechanistic understanding of how patterns of community structure arise requires linking processes from colonies to communities. Our study suggests the negative effects of dominant ant species on non-dominant species may be offset by mechanisms promoting coexistence.

Resource enrichment combined with biomass removal maintains plant diversity and community stability in a long-term grazed grassland

Abstract Aims Long-term heavy grazing reduces plant diversity and ecosystem function by intensifying nitrogen (N) and water limitation. In contrast, the absence of biomass removal can cause species loss by elevating light competition and weakening community stability, which is exacerbated by N and water enrichment. Hence, how to maintain species diversity and community stability is still a huge challenge for sustainable management of worldwide grasslands. Methods We conducted a 4-year manipulated experiment in six long-term grazing blocks to explore combination of resource additions and biomass removal (increased water, N and light availability) on species richness and community stability in semiarid grasslands of Inner Mongolia, China. Important Findings In all blocks treated with the combination of resource additions and biomass removal, primary productivity increased and species richness and community stability were maintained over 4 years of experiment. At both species and plant functional group (PFG) levels, the aboveground biomass of treated plants remained temporally stable in treatments with the combination of N and/or water addition and biomass removal. The maintenance of species richness was primarily caused by the biomass removal, which could increase the amount of light exposure for grasses under resource enrichment. Both species asynchrony and stability of PFGs contributed to the high temporal stability observed in these communities. Our results indicate that management practices of combined resource enrichment with biomass removal, such as grazing or mowing, could not only enhance primary productivity but also maintain plant species diversity, species asynchrony and community stability. Furthermore, as overgrazing-induced degradation and resource enrichment-induced biodiversity loss continue to be major problems worldwide, our findings have important implications for adaptive management in semiarid grasslands and beyond.

A landscape ecology assessment of land-use change on the Great Plains-Denver (CO, USA) metropolitan edge.

For better or worse, in those parts of the world with a widespread farming, livestock rising, and urban expansion, the maintenance of species richness and ecosystem services cannot depend only upon protected natural sites. Can they rely on a network of cultural landscapes endowed with their own associated biodiversity? We analyze the effects of land-cover change on landscape ecological patterns and processes that sustain bird species richness associated to cropland-grassland landscapes in the Great Plains-Denver metropolitan edge. Our purpose is to assess the potential contribution to bird biodiversity maintenance of Great Plain's cropland-grassland mosaics kept as farmland green belts in the edge of metropolitan areas. We present a quantitative landscape ecology assessment of land-cover changes (1930-2010) experienced in five Great Plains counties in Colorado. Several landscape metrics assess the diversity of land-cover patterns and their impact on ecological connectivity indices. These metrics are applied to historical land-cover maps and datasets drawn from aerial photos and satellite imagery. The results show that the cropland-grassland mosaics that link the metropolitan edge with the surrounding habitats sheltered in less human-disturbed areas provide a heterogeneous land matrix were a high bird species richness exists. They also suggest that keeping multifunctional farmland-grassland green belts near the edge of metropolitan areas may provide important ecosystem services, supplementing traditional conservation policies. Our maps and indicators can be used for selecting certain types of landscape patterns and priority areas on which biodiversity conservation efforts and land-use planning can concentrate.

Impact of windstorm on a community of centipedes (Chilopoda) in a beech forest in Western Poland

The study was carried out in the years 2016–2017, five years after a windstorm which destroyed 1/3 of the protected beech forest area in the west of Poland. The community of centipedes in the area affected by the windstorm was depleted in terms of the species richness, diversity, and population density. The dominance structures were shortened and the species composition was rebuilt. The areas that proved to be the richest in terms of species richness and diversity among the sites affected by the windstorm were the one where windfallen trees were left and the other where beech trees had been planted by humans. In total, the quantitative and qualitative samples collected four times throughout a year featured 608 specimens from 11 species of two centipede orders – Lithobiomorpha and Geophilomorpha. Lithobius curtipes and L. forficatus were found in all of the investigated areas. L. pelidnus and L. piceus were captured at control sites exclusively. Only one species –L. erythrocephalus was found solely at the damaged site. The most numerous and most frequently found species in the community were L. curtipes, L. mutabilis, and Strigamia acuminata respectively. Although windstorms are natural phenomena their consequences may lead to significant changes in the community of the investigated soil animals. The importance of coarse woody debris, significantly contributing to the improvement and maintenance of species richness and diversity of Chilopoda, has once again been confirmed.

Effect of cutting frequency on species richness and dry matter yield of permanent grassland after grazing cessation

ABSTRACTThe effect of grazing cessation management has only rarely been investigated. In this study, the influence of cutting regime in the absence of fertilization was examined during 2005–2011 on a semi-natural grassland in Rapotin (Czech Republic) which had been grazed for more than 30 years before the start of the trial. This was conducted as a randomized plot design with five levels of treatment: 4 C – intensive (four cuts per year); 3 C – medium intensive (three cuts per year); 2 C – low intensive (two cuts per year); 1 C – extensive (one cut per year); 0 C – abandoned (control; without any management). Species richness was significantly lower in treatments 1 C and 0 C than in other treatments. Management and year had similar and significant influence on species composition and explained 23% of its variability. Dry matter (DM) yields were found to be lower in three-cut than in two-cut treatments (5.56 t ha−1 and 6.22 t ha−1, respectively). In the case of grazing cessation, a suitable compromise of three cuts per year can be recommended to guarantee maintenance of species richness, botanical composition, and appropriate grass forage yield under similar site conditions.

INTRA-GUILD COMPENSATION REGULATES SPECIES RICHNESS IN DESERT RODENTS: REPLY

Evidence from numerous studies suggests that species richness is an emergent property of local communities. The maintenance of species richness, despite changes in species composition and environmental conditions, requires compensatory colonization and extinction events with species coming from a regional pool. Using long-term data from a rodent community in the Chihuahuan Desert, we use randomization methods to test the null hypothesis that changes in species richness occur randomly. We find that the dynamics of species richness differ significantly from a random process, and that these nonrandom dynamics occur largely within the most speciose guild. Finally, we propose a general framework for assessing the importance of species compensation in maintaining biodiversity within local communities. Our results highlight the importance of niche complementarity and compensation in maintaining relatively constant species richness over time.

Trait convergence and trait divergence in herbaceous plant communities: Mechanisms and consequences

Abstract In landscapes subject to intensive agriculture, both soil fertility and vegetation disturbance are capable of impacting strongly, evenly and simultaneously on the herbaceous plant cover and each tends to impose uniformity on the traits of constituent species. In more natural and ancient grasslands greater spatial and temporal variation in both productivity and disturbance occurs and both factors have been implicated in the maintenance of species-richness in herbaceous communities. However, empirical data suggest that disturbance is the more potent driver of trait differentiation and species co-existence at a local scale. This may arise from the great diversity in opportunities for establishment, growth or reproduction that arise when the intensity of competition is reduced by damage to the vegetation. In contrast to the diversifying effects of local disturbances, productivity-related plant traits (growth rate, leaf longevity, leaf chemistry, leaf toughness, decomposition rate) appear to be less v...

INTRA-GUILD COMPENSATION REGULATES SPECIES RICHNESS IN DESERT RODENTS

Evidence from numerous studies suggests that species richness is an emergent property of local communities. The maintenance of species richness, despite changes in species composition and environmental conditions, requires compensatory colonization and extinction events with species coming from a regional pool. Using long-term data from a rodent community in the Chihuahuan Desert, we use randomization methods to test the null hypothesis that changes in species richness occur randomly. We find that the dynamics of species richness differ significantly from a random process, and that these nonrandom dynamics occur largely within the most speciose guild. Finally, we propose a general framework for assessing the importance of species compensation in maintaining biodiversity within local communities. Our results highlight the importance of niche complementarity and compensation in maintaining relatively constant species richness over time.

Perspectives on development of definitions and values related to old-growth forests

Old-growth forests are those that meet some threshold(s) determined by a scientific and political process. The main issue is what criteria to use to determine these thresholds; they must be practical enough to allow managers to delimit and manage old-growth stands in the field. People value forests with old and (or) big trees and primary forests that have a continuous heritage of natural disturbance and regeneration, even though the latter may include all stages of stand development and succession. We advocate uniting these two and using "primary forest", also called "natural heritage forest", as the criterion for delimiting old growth in regions where primary forest still exists. This criterion recognizes that the stage of development with big, old trees is part of a cycle of development, and it is necessary to have all the parts to continue to produce new examples of the older stages. The best available second-growth stands can be used in regions where primary forests are not available. Alternatively, threshold criteria for delimiting old growth can be based on tree size and age, but arbitrary criteria based on human size and age scales should be avoided in favour of criteria that specify stands dominated by trees relatively large and old for the species and site. Such criteria allow for old growth to occur across a variety of levels of site productivity, with trees of widely varying stature and with varying life-history characteristics, such as longevity, shade tolerance, and successional status. In any case, managers and scientists should work together to make sure that definitions work in the field but also include the ecological processes necessary to maintain the unique biological resources of old growth. The biological resources present in old growth may help to restore the second-growth landscape and allow reconstitution of forests in new places after global warming. Old-growth forests provide a baseline for comparison of effects of logging and natural disturbance, with respect to resilience to climatic change and disturbance, maintenance of species richness, and natural genetic structure of tree populations, which respond to different selective regimes in old growth and harvested forests. The species in old-growth remnants, their interactions and the resilience of the system after disturbance are as important or perhaps more so than the age and size of the trees at a given point in time. Key words: dwarf forest, Minnesota, old-growth processes, tree height.

Regulation of diversity: maintenance of species richness in changing environments.

In order to assess how diversity changes over time at sites undergoing environmental change, we examined three data sets on long-term trends in taxonomic richness and composition: (1) 22years of rodent censuses from a site in the Chihuahuan Desert of Arizona; (2) 50years of bird surveys from a three-county region of northern Michigan; and (3) approximately 10,000years of pollen records from two sites in Europe. In all three cases, richness has remained remarkably constant despite large changes in composition. The results suggest that while species composition may be highly variable and change substantially in response to environmental change, species diversity is an emergent property of ecosystems that is often maintained within narrow limits. Such regulation of diversity requires maintenance of relatively constant levels of productivity and resource availability and an open system with opportunity for compensatory colonizations and extinctions. In addition to studying the effects of diversity on biogeochemical processes, it will often be useful to think of species richness as an emergent consequence of ecosystem processes.

Patch implications in the maintenance of species richness in an isolated forest site

Plant species richness as a function of patchiness of three different management types, viz. clear-felled, selective-cut and protected, was evaluated in an abandoned urban forest in central Japan. One-hundred and thirty-seven vascular species were recorded at the understory in this 3.2 ha planted forest stand of indigenous conifer — Cryptomeria japonica and Chamaecyparis obtusa. These species included 52.5% herb, 13.9% climber, 15.3% shrub and 18.2% tree species. This species diversity was sustained by dynamic attributes of the patches which were generated and modified by disturbances originating from human activities and natural processes. Past management practices contributed largely to the variation of canopy openings, and continued human activities such as trampling added heterogeneity by soil compaction. These anthropogenic and natural disturbances interacted to effect the pattern of plant species diversity and composition.

An exploration of factors influencing lotic insect species richness

An understanding of factors that influence species richness of lotic insects is generally lacking. We present comparative data on aquatic insect species richness from several North American and other streams. Factors such as large sample numbers and drainage area (species area relationships) are not significant predictors of species richness across the streams we examined. We explore several hypotheses regarding the origins and maintenance of species richness using Upper Three Runs Creek (UTR), South Carolina, USA, as a reference stream. UTR has the highest species richness of any stream in the Western Hemisphere. Hypotheses examined included historical, regional and local processes such as: (1) Evolutionary time, (2) disturbance regime/environmental variability, (3) temperature/evolutionary-speed, (4) productivity, and (5) habitat heterogeneity. Of these hypotheses, we suggest that productivity and habitat heterogeneity appear to contribute most to the high species richness found in UTR. We believe that multidisciplinary analysis of other streams is necessary because without this crucial information our knowledge of, and desire to protect biodiversity in streams will be wanting.

Strangler fig‐host associations in roadside and deciduous forest sites, South India

Abstract. Understanding the regeneration niche of animal‐dispersed epiphytes is important in understanding forest community structure, maintenance of species richness in plant communities, animal movements and distributions, and in managing plant and animal communities for conservation. Strangler figs are particularly interesting for studying epiphyte‐host relations because they are hemiepiphytes, implying that strangler and host can potentially belong to the same species and either fuse together or strangle each other, and because all stranglers have many‐seeded, animal‐dispersed fruit, providing many opportunities for seed dispersal to other stranglers. A study was conducted at a roadside and at a forest site in Karnataka State, south India, to determine factors influencing host choice of strangler figs. Stranglers were found more frequently at the roadside site than at the forest site. At the roadside site, stranglers were found much more abundantly on Ficus hosts than on non‐Ficus hosts, whereas at the forest site, stranglers were found more abundantly on non‐Ficus hosts. Host tree species with animal‐dispersed fruit bore significantly more stranglers than those with mechanically dispersed fruit. More stranglers were found on hosts in large d.b.h. size classes (>80 cm d.b.h.) than on those in small d.b.h. classes. Prior studies of strangler‐host relations have never found stranglers growing on other stranglers. The results of this study suggest that stranglers are fully capable of regenerating on other stranglers, including conspecifics, but these regeneration events are not observed in forests because of relatively low strangler seed rain, due to lack of clumping of strangler hosts, and low insolation in these habitats.

Integrating agricultural land-use and management for conservation of a native grassland flora in a variegated landscape

Management of variegated landscapes (in which the native vegetation still forms the matrix but has been modified in a variable way) requires strategies to maintain or enhance existing vegetation within the context of human land-uses such as agriculture. Using rangelands in the New England region of New South Wales as an example, spatial patterns of land-use and modification are described. Management principles for conservation of herbaceous communities in areas of pastoral production are suggested, based on the following assumptions: 1) low intensity pasture utilization and management (i.e., limited fertilization, soil disturbance and grazing) is conducive to the maintenance of species richness at a local and regional scale; 2) stratification of management intensity on farms is compatible with viable grazing operations; 3) landscape context is important as effects of management may spread beyond the managed area; 4) spatial arrangement of land-uses could be optimized to maintain or increase diversity. Although our understanding of these issues is incomplete, there is general observational and theoretical support for them. Incorporation of principles derived from these assumptions in the farm planning process is a useful strategy for preserving grassland vegetation in landscapes where opportunities for reserve conservation are limited.

The Estero de Punta Banda, B.C., Mexico as a link in the "Pacific Flyway": Abundance of shorebirds

Thirteen shorebird species and 5683 individuals were recorded at Estero Punta Banda from October 1988 to April 1989 in three soft-bottom habitats bordering the northern tip of the sand bar (open beach; terminal beach; mud-flats) and a semi-protected seasonal pond at the southwest comer of the estuary. The open beach (seven species; 1310 individuals), mud-flats (13 species; 3958 individuals) and the pond (two species; 146 individuals) harbored distinctive species assemblages while the terminal beach (five species; 239 individuals) acted as an extension of the open beach and mud flats. Most species where exclusive of a single habitat, or almost exclusive (species that occur in more that one habitat but exhibit strong quantitative differences among them). Seasonal changes were rather neat, although the study period missed the first part of the autumn migration towards the south. Seasonal movements were not synchronic in the different habitats. We estimated that about 14,000 shorebirds visit the lagoon each season (3,000 in the open beach; 11,000 in mud-flats). Although most species had been recorded for the site, quantitative data and evidence of the role of estero Punta Banda along the Pacific Flyway are offered in this study for the first time. Distinctive species assemblages in the different habitats, and asynchronism of migration in each, show that patchiness of habitats is important for the maintenance of species richness and for the conservation of the migratory process as well.

Distribution of Vascular Plant Species in Small Woodlands on the Western Carpathian Foothills

Sixty-nine woodlands isolated in the agricultural landscape of the Wierzban6wka valley (Western Carpathian foothills) were investigated. An analysis of historical maps shows that most of the woods under study are remnants of ancient woodlands. Stepwise and partial regression analyses were used in the statistical study of 66 small woods. It was found that the number of woodland vascular plant species depended upon area, isolation, shape, period of isolation and anthropogenic disturbances. Recent woods are poorer in species than the ancient ones. Single ancient woods on average support fewer species than does a combination of several small ancient woods of the same total area. The distribution of 58 common and 56 locally rare woodland species was analysed. The group of common species associated with more recently isolated and less disturbed woods contained more myrmecochores, endozoochores and epizoochores and fewer anemochores than did the group of indifferent species. This last group included more species capable of colonizing recent woods. The number of woodland species appeared to be the most important predictor of the number of rare species. The results obtained and their comparison with the results from other similar studies indicate that small remnants of ancient forests in an agricultural landscape are refuges of numerous woodland species. Therefore, the preservation of such woods carries great weight in the maintenance of species richness and the protection of woodland species.

Protandry in Physiological Time

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