Maintenance Of High Species Richness Research Articles

Local habitat factors and spatial connectivity jointly shape an urban insect community

As the world becomes more and more urbanized, it is increasingly important to understand the impacts of urban landscapes on biodiversity. Urbanization can change local habitat factors and decrease connectivity among local habitats, with major impacts on the structure of natural food webs. However, most studies have focused on single species, or compared rural to urban habitats, which do not inform us on how to design and manage cities to optimize biodiversity. To understand the local and spatial drivers of ecological communities within urban landscapes, we assessed the relative impact of local habitat factors (sunlight exposure and leaf litter) and spatial connectivity on an oak-associated herbivore community within an urban landscape. From the local habitat factors, leaf litter but not sunlight exposure was related to herbivore species richness, with leaf litter contributing to the maintenance of high species richness on isolated trees. Guilds and species differed strongly in their response to local habitat factors and connectivity, resulting in predictable variation in insect community composition among urban oaks. Taken together, our study shows an interactive effect of local and spatial factors on species richness and species composition within an urban context, with guild- and species-specific life histories determining the response of insects to urban landscapes. To maintain biodiversity in the urban landscape, preserving a dense network of local habitats is essential. Moreover, allowing leaf litter to accumulate can be a simple, cost-effective conservation management practice.

Habitat filtering drives the local distribution of congeneric species in a Brazilian white-sand flooded tropical forest.

The investigation of ecological processes that maintain species coexistence is revealing in naturally disturbed environments such as the white‐sand tropical forest, which is subject to periodic flooding that might pose strong habitat filtering to tree species. Congeneric species are a good model to investigate the relative importance of ecological processes that maintain high species diversity because they tend to exploit the same limiting resources and/or have similar tolerance limits to the same environmental conditions due to their close phylogenetic relationship. We aim to find evidence for the action and relative importance of different processes hypothesized to maintain species coexistence in a white‐sand flooded forest in Brazil, taking advantage of data on the detailed spatial structure of populations of congeneric species. Individuals of three Myrcia species were tagged, mapped, and measured for diameter at soil height in a 1‐ha plot. We also sampled seven environmental variables in the plot. We employed several spatial point process models to investigate the possible action of habitat filtering, interspecific competition, and dispersal limitation. Habitat filtering was the most important process driving the local distribution of the three Myrcia species, as they showed associations, albeit of different strength, to environmental variables related to flooding. We did not detect spatial patterns, such as spatial segregation and smaller size of nearby neighbors, that would be consistent with interspecific competition among the three congeneric species and other co‐occurring species. Even though congeners were spatially independent, they responded to differences in the environment. Last, dispersal limitation only led to spatial associations of different size classes for one of the species. Given that white‐sand flooded forests are highly threatened in Brazil, the preservation of their different habitats is of utmost importance to the maintenance of high species richness, as flooding drives the distribution of species in the community.

Effects of landscape modification on species richness patterns of fruit‐feeding butterflies in Brazilian Atlantic Forest

AbstractAimTo assess the distributional patterns of fruit‐feeding butterfly species richness in Atlantic Forest (AF) based on stack species distribution models (SSDM); to evaluate the relative contribution of climate and landscape in the patterns of butterfly species richness; and to recommend conservation guidelines for AF regions based on the obtained results.LocationBrazilian Atlantic Forest.MethodsWe used SSDMs to generate potential distribution maps of butterfly species richness in AF. Our dataset comprises 7,062 records of 279 species, distributed across 122 local communities. We built richness maps based on climate and landscape models and analysed them separately to understand their contribution to the pattern of richness distribution. Then, we combined both models to build a consensus map. Finally, we designed specific conservation strategies based on richness categories distributed on the consensus map.ResultsThe regions with high‐predicted species richness for both climate and landscape models supported the main endemism locations described for other AF taxa in previous studies. Both models predicted intermediate values of species richness for most regions, but the patterns of richness distribution were not fully congruent. High species richness based on landscape metrics was frequently concentrated in the south. Furthermore, locations suitable for high species richness according to climate are near to the endemism centres, but also to dense urban centres, highlighting the potential impacts of the landscape modification on butterfly species richness.Main conclusionsThe distribution of fruit‐feeding butterfly species richness and endemism reflect the classic division of AF in different sub‐regions according to the endemism centres proposed by previous authors for other taxa. The availability of forested habitats seems to be a determining factor for the maintenance of high species richness in AF. Therefore, the loss of natural forest remnants due to landscape modification is the primary threat to butterfly diversity.

Progression and stability analysis of rain forest tree growth under environmental stochasticity

AbstractChanges in relative stem growth rate (rgr) across periods of multi‐censused plot data in tropical forest allow response indices (RIs) to be related to environmental (climatic) variation over time. Among small trees (12.5 to <50 cm girth at breast height [gbh]) in two permanent 4‐ha plots at Danum, Sabah, Borneo (lowland dipterocarp formation), growth responses were followed before, during, and after a major ENSO drying event in 1998 (censuses of 1986, 1996, 1999, 2001, and 2007 in subplots). Overall, RI was negative in the interval with the drought, increased or reflected overcompensation in rgr immediately afterwards, and then settled back to pre‐event levels. However, among the various tree species, responses and trajectories were very different: Some species showed positive or negative trends, while others showed stabilizing ones, and several had stable and unstable oscillations. Response index was graphed for pairs of periods in two ways: “consecutive” and “constitutive,” allowing, respectively, progression (fundamental, implicit and explicit) and stability (fundamental, intended, and extended) to be examined. Strongest RIs were found among the understory species. Variation in RI was, nevertheless, very high between individuals within species and masked most average species' differences. Environmental stochasticity appears to lead to strong mixing effects of species composition over time, not necessarily randomly, but in a highly complicated manner depending on tree size, topographic location, neighborhood, and over–understory status, which would compound demographic stochasticity in recruitment to the small‐tree class. Fluctuating responses cascade over one another in a highly unpredictable manner. These pluralistic responses may form the basis to a new understanding of tree population dynamics within the forest ecosystem, and to an improved theory about the maintenance of high species richness. Plasticity in allocation of resources to roots vs. shoots under water limitation offers a feasible hypothesis for high individual variation in growth. Instead of tropical rain forests being viewed as “complex,” an empirically more sound way is to regard them as being highly “complicated” within a mechanistic and functional approach. Multi‐species tree population dynamics are accordingly highly unpredictable and quasi‐indeterminate.

The Relationship between Species Richness and Evenness in Plant Communities along a Successional Gradient: A Study from Sub-Alpine Meadows of the Eastern Qinghai-Tibetan Plateau, China

The relationship between species richness and evenness across communities remains an unsettled issue in ecology from both theoretical and empirical perspectives. As a result, we do not know the mechanisms that could generate a relationship between species richness and evenness, and how this responds to spatial scale. Here we examine the relationship between species richness(S) and evenness (Pielou’s J′ evenness) using a chronosequence of successional sub-alpine meadow communities in the eastern Qinghai-Tibetan Plateau. These meadows range from natural community (never farmed), to those that have been protected from agricultural exploitation for periods ranging from 1 to 10 years. A total of 30 sampling quadrats with size of 0.5 m×0.5 m were laid out along two transects at each meadow. Using correlation analyses we found a consistent negative correlation between S and J′ in these communities along the successional gradient at the sampling scale of 0.5 m×0.5 m. We also explored the relationship between S and J′ at different sampling scales (from 0.5 m×0.5 m to10 m×10 m) using properly measured ramet-mapped data of a10 m×10 m quadrat in the natural community. We found that S was negatively corrected with J′ at the scales of 0.5 m×0.5 m to 2 m×2 m, but such a relationships disappeared at relative larger scales (≥2 m×4 m). When fitting different species abundance models combined with trait-specific methods, we found that niche preemption may be the determining mechanism of species evenness along the succession gradient. Considering all results together, we can conclude that such niche differentiation and spatial scale effects may help to explain the maintenance of high species richness in sub-alpine meadow communities.

Evaluating the role of contracting and expanding rainforest in initiating cycles of speciation across the Isthmus of Panama

Climatic and geological changes across time are presumed to have shaped the rich biodiversity of tropical regions. However, the impact climatic drying and subsequent tropical rainforest contraction had on speciation has been controversial because of inconsistent palaeoecological and genetic data. Despite the strong interest in examining the role of climatic change on speciation in the Neotropics there has been few comparative studies, particularly, those that include non-rainforest taxa. We used bird species that inhabit humid or dry habitats that dispersed across the Panamanian Isthmus to characterize temporal and spatial patterns of speciation across this barrier. Here, we show that these two assemblages of birds exhibit temporally different speciation time patterns that supports multiple cycles of speciation. Evidence for these cycles is further corroborated by the finding that both assemblages consist of 'young' and 'old' species, despite dry habitat species pairs being geographically more distant than pairs of humid habitat species. The matrix of humid and dry habitats in the tropics not only allows for the maintenance of high species richness, but additionally this study suggests that these environments may have promoted speciation. We conclude that differentially expanding and contracting distributions of dry and humid habitats was probably an important contributor to speciation in the tropics.

Environmental factors related to anuran assemblage composition, richness and distribution at four large rivers under varied impact levels in southeastern Brazil

AbstractThe margins of large rivers are usually impacted by human settlements and activities, which may affect the occupancy and use of riparian habitats by many organisms. Among vertebrates, amphibians are likely the most sensitive to environmental changes, and they can be used as a model to identify attributes of the riparian habitats that are important for the maintenance of high species richness and functional diversity. We studied anuran assemblages in four large rivers of the Velhas River basin in southeastern Brazil during one year, focusing on features of the rivers and riparian habitats that influence species distribution. We tested whether a river under greater anthropogenic impact would shelter less species compared to three rivers of equivalent size under lower impact level, and whether lower species richness related to lower availability of preferred microhabitats. We found soil type at river margin and riparian vegetation structure to be the main factors influencing anuran distribution. Species richness was positively related to microhabitat diversity and availability of preferred microhabitats, which were the lowest in the most impacted river. Most species recorded at the rivers were not breeding there, and were present in larger numbers during the dry season, when temporary bodies of water dry at the vicinities of the large rivers. Conservation of a broad extension of the riparian habitat (200 m or more) would be efficient both to provide appropriate microhabitats for anurans and to maintain connectivity between breeding sites and large, permanent rivers used by several species during the dry season. Copyright © 2010 John Wiley & Sons, Ltd.

Aquatic Biodiversity in the Amazon: Habitat Specialization and Geographic Isolation Promote Species Richness.

Simple SummaryThe immense rainforest ecosystems of tropical America represent some of the greatest concentrations of biodiversity on the planet. Prominent among these are evolutionary radiations of freshwater fishes, including electric eels, piranhas, stingrays, and a myriad of small-bodied and colorful tetras, cichlids, and armored catfishes. In all, the many thousands of these forms account for nearly 10% of all the vertebrate species on Earth. This article explores the complimentary roles that ecological and geographic filters play in limiting dispersal in aquatic species, and how these factors contribute to the accumulation of species richness over broad geographic and evolutionary time scales.The Neotropical freshwater ichthyofauna has among the highest species richness and density of any vertebrate fauna on Earth, with more than 5,600 species compressed into less than 12% of the world's land surface area, and less than 0.002% of the world's total liquid water supply. How have so many species come to co-exist in such a small amount of total habitat space? Here we report results of an aquatic faunal survey of the Fitzcarrald region in southeastern Peru, an area of low-elevation upland (200–500 m above sea level) rainforest in the Western Amazon, that straddles the headwaters of four large Amazonian tributaries; the Juruá (Yurúa), Ucayali, Purús, and Madre de Dios rivers. All measures of fish species diversity in this region are high; there is high alpha diversity with many species coexisting in the same locality, high beta diversity with high turnover between habitats, and high gamma diversity with high turnover between adjacent tributary basins. Current data show little species endemism, and no known examples of sympatric sister species, within the Fitzcarrald region, suggesting a lack of localized or recent adaptive divergences. These results support the hypothesis that the fish species of the Fitzcarrald region are relatively ancient, predating the Late Miocene-Pliocene (c. 4 Ma) uplift that isolated its several headwater basins. The results also suggest that habitat specialization (phylogenetic niche conservatism) and geographic isolation (dispersal limitation) have contributed to the maintenance of high species richness in this region of the Amazon Basin.

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

Summary1. 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.

SOIL VS. CANOPY SEED STORAGE AND PLANT SPECIES COEXISTENCE IN SPECIES-RICH AUSTRALIAN SHRUBLANDS

The fire-prone shrublands of southwestern Australia are renowned for their high plant species diversity and prominence of canopy seed storage (serotiny). We compared species richness, abundance, and life history attributes for soil and canopy seed banks in relation to extant vegetation among four sites with different substrate conditions and high species turnover (50-80%) to identify whether this unusual community-level organization of seed storage might contribute to maintenance of high species richness. Soil seed bank (SSB) densities were low to moderate (233-1435 seeds/m2) compared with densities for other Mediterranean-type vegetation and were lowest for sites with highest canopy seed bank (CSB) species richness and lowest nutrient availability, but not richness or abundance of resprouters. Annuals were infrequent in the lowest nutrient sites, but there was no evidence that small SSB size was due to low seed inputs or a trade-off between seed production/storage and seed size in response to low nutrient availability. Sorensen's similarity between SSB and extant vegetation was 26-43% but increased to 54-57% when the CSB was included, representing levels higher than reported for most other ecosystems. Resprouting species were well represented in both the SSB and CSB, and there was no evidence for lower seed production in resprouters than in non-sprouters overall. The SSB and CSB held no species in common and were characterized by markedly different seed dispersal attributes, with winged or small seeds in the CSB and seeds dispersed by ants, birds, and wind (though none with wings) in the SSB. There was no evidence of spatial differentiation in the distribution of seeds of SSB species between vegetated and open microsites that might facilitate species coexistence, but most woody non-sprouters showed aggregation at scales of 1-2 m, implying limited seed dispersal. High similarity between overall seed bank (SSB + CSB) and extant species composition, high number of resprouting species, and seed dispersal processes before (SSB) and after fire (CSB) leading to differential spatial aggregation of post-fire recruits from the two seed bank types may buffer species composition against rapid change and provide a mechanism for maintaining species coexistence at the local scale.

Seed Dispersal, Seed Predation, and Juvenile Mortality of Aglaia sp. (Meliaceae) in Lowland Dipterocarp Rainforest

Black hornbills (Anthracoceros malayanus) appear to be the principal long-distance seed dispersers of Aglaia sp. (Meliaceae) at Pasoh Forest Reserve in Peninsular Malaysia. The squirrel Callosciurus prevostii removed some of the large seeds at least as far as adjacent crowns and sometimes dropped them after consuming only the orange, oily sarcotesta. It chased other squirrel species, which are probably seed predators, and hornbills out of the fruiting crown. Seeds on the ground beneath the parent crown were removed more rapidly than those farther away by rodent and (possibly) phasianid seed predators. Sitophilus sp. (Curculionidae) was also an Aglaia seed predator or parasite. Aglaia juveniles grew slowly under closed canopy, and small ones (<50 cm in height) had only 9.7 percent mortality per year during a 4-year period. Seedling survival was positively size dependent. For unknown reasons, small seedlings near the parent had a higher death rate than those at a greater distance; this was apparently a long-term pattern, because large seedlings and saplings did not occur within 10 and 35 m, respectively, of the parent tree's base. For this species an advantage of seed dispersal is avoidance of disproportionate seed and seedling mortality near the parent. Although Aglaia grows much faster in gaps than under closed canopy, it may require several episodes of growth in successive gaps before becoming reproductively mature. IN THEIR REVIEW OF SEED DISPERSAL, Howe and Smallwood (1982) remarked that little is known about its ecological and evolutionary advantages to the plant. Here we combine observations on seed dispersal and predation and juvenile mortality and spatial distribution to show how dispersal helps the tropical tree Aglaia sp. (Meliaceae) avoid seed and seedling mortality that is greater near the parent than farther away. Webb et al. (1967), Janzen (1970), and Connell (1971) suggested that such a mortality pattern, generated by seed predators, herbivores, or allelopathy, would promote the maintenance of high tree species richness in tropical forests. More recently, Connell (1978, 1979) has withdrawn his support for this hypothesis because field studies have shown that seed and seedling mortality is not invariably higher near conspecific adults. However, Clark and Clark's (1984) review of 24 data sets on mostly neotropical, woody plants showed that most evidence indicates either densityor distance-dependence in progeny mortality, as originally predicted by Janzen and Connell. Hubbell (1979, 1980) challenged the Janzen-Connell hypothesis on empirical and theoretical grounds, daiming the latter to demonstrate that spacing between conspecific adults could contribute little to the maintenance of high species richness. His theoretical analysis has been questioned by Becker et al. (1985), who consider the issue unresolved for nonequilibrium

Distribution of Photosynthetically Active Radiation in the Canopy of a Loblolly Pine Plantation

The landscape in sand dune areas is characterized by the alternate distribution of sand dune and interdune lowland, and the unique floras in these areas are some endemic or rare plant species. In recent years, the decrease in plant species richness and the disappearance of some endemic or rare plant species in these areas have been received special attention, which were listed in the Program of International Biodiversity Conservation, and studied in many countries and districts. In this paper, the research progress in these fields was summarized from the aspects of significance of plant diversity conservation, formation mechanisms of plant diversity, ways of plant diversity conservation, roles of plant diversity research in the development of ecological theories, and important issues in operating plant diversity conservation project. To conserve plant diversity in sand dune areas, attentions should be paid to the differences in conservation goals (to maintain high species richness or to conserve endemic or rare species) among different regions, and the balances between the stabilization of active sand and the conservation of endemic or rare species, and the maintenance of high species richness and the conservation of endemic or rare species. It needed also to consider the sand dune and the interdune lowland as a unified landscape unit to explore the impacts of disturbances and habitat fragment on plant diversity.