Species richness

About: Species richness is a research topic. Over the lifetime, 61672 publications have been published within this topic receiving 2183796 citations.

Determining the relative roles of species replacement and species richness differences in generating beta‐diversity patterns

Abstract: Aim To determine the relative contribution of species replacement and species richness differences to the emergence of beta-diversity patterns. Innovation A novel method that disentangles all compositional differences (βcc, overall beta diversity) in its two components, species replacement (β-3) and species richness differences (βrich) is proposed. The performance of the method was studied with ternary plots, which allow visualization of the influence of the relative proportions of shared and unique species of two sites over each metric. The method was also tested in different hypothetical gradients and with real datasets. The novel method was compared with a previous proposal based on the partitioning of overall compositional differences (βsor) in replacement (βsim) and nestedness (βnes). The linear response of βcc contrasts with the curvilinear response of βsor to linear gradients of dissimilarity. When two sites did not share any species, βsim was always 1 and β-3 only reached 1 when the number of exclusive species of both sites was equal. β-3 remained constant along gradients of richness differences with constant replacement, while βsim decreased. βrich had a linear response to a linear gradient of richness differences with constant species replacement, whereas βnes exhibited a hump-shaped response. Moreover, βsim > βnes when clearly almost all species of one site were lost, whereas β-3 < βrich in the same circumstances. Main conclusions The behaviour of the partition of βcc into β-3 and βrich is consistent with the variation of replacement and richness differences. The partitioning of βsor into βsim and βnes overestimates the replacement component and underestimates richness differences. The novel methodology allows the discrimination of different causes of beta-diversity patterns along latitudinal, biogeographic or ecological gradients, by estimating correctly the relative contributions of replacement and richness differences.

Contrasting effects of invasive plants in plant-pollinator networks.

Abstract: The structural organization of mutualism networks, typified by interspecific positive interactions, is important to maintain community diversity However, there is little information available about the effect of introduced species on the structure of such networks We compared uninvaded and invaded ecological communities, to examine how two species of invasive plants with large and showy flowers (Carpobrotus affine acinaciformis and Opuntia stricta) affect the structure of Mediterranean plant-pollinator networks To attribute differences in pollination to the direct presence of the invasive species, areas were surveyed that contained similar native plant species cover, diversity and floral composition, with or without the invaders Both invasive plant species received significantly more pollinator visits than any native species and invaders interacted strongly with pollinators Overall, the pollinator community richness was similar in invaded and uninvaded plots, and only a few generalist pollinators visited invasive species exclusively Invasive plants acted as pollination super generalists The two species studied were visited by 43% and 31% of the total insect taxa in the community, respectively, suggesting they play a central role in the plant-pollinator networks Carpobrotus and Opuntia had contrasting effects on pollinator visitation rates to native plants: Carpobrotus facilitated the visit of pollinators to native species, whereas Opuntia competed for pollinators with native species, increasing the nestedness of the plant-pollinator network These results indicate that the introduction of a new species to a community can have important consequences for the structure of the plant-pollinator network

Response Time of Wetland Biodiversity to Road Construction on Adjacent Lands

Abstract: Road construction may result in significant loss of biodiversity at both local and regional scales due to restricted movement between populations, increased mortality, habitat fragmentation and edge effects, invasion by exotic species, or increased human access to wildlife habitats, all of which are expected to increase local extinction rates or decrease local recolonization rates. Species loss is unlikely to occur immediately, however. Rather, populations of susceptible species are expected to decline gradually after road construction, with local extinction occurring sometime later. We document lags in wetland biodiversity loss in response to road construction by fitting regression models that express species richness of different taxa ( birds, mammals, plants, and herptiles) as a function of both current and historical road densities on adjacent lands. The proportion of variation in herptile and bird richness explained by road densities increased significantly when past densities were substituted for more current densities in multiple regression models. Moreover, for vascular plants, birds, and herptiles, there were significant negative effects of historical road densities when the most current densities were controlled statistically. Our results provide evidence that the full effects of road construction on wetland biodiversity may be undetectable in some taxa for decades. Such lags in response to changes in anthropogenic stress have important implications for land-use planning and environmental impact assessment.

Relationships between benthic biota and hydrological indices in New Zealand streams

Abstract: SUMMARY 1. The objective of this study was to identify the most ecologically relevant hydrological indices for characterizinghydrological regimes in New Zealand streams' To do this we related measures of periphyton chlorophyll o, ash-free dry mass (AFDM' species richness, and diversity and invertebrate density, species richness and diversity, ta thirty-four hydrological variables derived from daily flow records at eighty-three sites. Tire hydrologicai variables included some describing average flow conditions, flow variability, floods, and low-flow characteristics' Z. A principal components analysis showed that the interrelationship between many of the hyarological variables was high, and most variables correlated significantly with princlpil Component 1 (PC1). The flood frequency variables formed a distinct component of the flow regime and were the main contributor to PC2' g. We found that both the average flow conditions and some rieasure of variability were significantly related to most of the biological variables, and these individual hydrolo-gical variables were more strongly correlated to the biological measures than the "amposit" principal components. Only four of the thirty-four flow variables were signi-ficantþ "ortalut"d 1Þ < O.OSi with measures of periphyton biomass (chlorophyll o utia epiVf), whereas twenty-four variables were correlated with periphyton diversity' Conversely, thirty-one of the thirty-four flow variables were correlated with total invertebraie density, whereas only four variables correlated with diversity' 4. We selected the flood frequency (FRE3), where a flood is defined as flows higher than three times the median flow, as the most ecological useful oaerall flow variable in New Zealand streams becausq it explained a significant amount of the variance in four out of the six main benthic community measures, and it had a clear mechanism of control of the biota which was commensurate with current stream ecosystem theory' Periphyton biomass decreased with increasing FRE3, whereas invertebrate density had an increasing/curvilinear relationship with FRE3. Periphyton species richness and diversity decreased with increasing FRE3.

Agroforestry systems conserve species-rich but modified assemblages of tropical birds and bats

Abstract: Although an increasing number of studies have shown that diverse, multi-strata agroforestry systems can contribute to the conservation of tropical biodiversity, there is still debate about how the biodiversity within agroforestry systems compares to that of intact forest and alternative land uses. In order to assess the relative importance of agroforestry systems for biodiversity conservation, we characterized bat and bird assemblages occurring in forests, two types of agroforestry systems (cacao and banana) and plantain monocultures in the indigenous reserves of Talamanca, Costa Rica. A total of 2,678 bats of 45 species were captured, and 3,056 birds of 224 species were observed. Agroforestry systems maintained bat assemblages that were as (or more) species-rich, abundant and diverse as forests, had the same basic suite of dominant species, but contained more nectarivorous bats than forests. Agroforestry systems also contained bird assemblages that were as abundant, species-rich and diverse as forests; however the species composition of these assemblages was highly modified, with fewer forest dependent species, more open area species and different dominant species. The plantain monocultures had highly modified and depauperate assemblages of both birds and bats. Across land uses, bird diversity and species richness were more closely correlated with the structural and floristic characteristics than were bats, suggesting potential taxon-specific responses to different land uses. Our results indicate that diverse cacao and banana agroforestry systems contribute to conservation efforts by serving as habitats to high numbers of bird and bat species, including some, but not all, forest-dependent species and species of known conservation concern. However, because the animal assemblages in agroforestry systems differ from those in forests, the maintenance of forests within the agricultural landscape is critical for conserving intact assemblages at the landscape level.