Turnover In Ecosystems Research Articles

CsRAXs negatively regulate leaf size and fruiting ability through auxin glycosylation in cucumber.

Leaves are the main photosynthesis organ that directly determines crop yield and biomass. Dissecting the regulatory mechanism of leaf development is crucial for food security and ecosystem turn-over. Here, we identified the novel function of R2R3-MYB transcription factors CsRAXs in regulating cucumber leaf size and fruiting ability. Csrax5 single mutant exhibited enlarged leaf size and stem diameter, and Csrax1/2/5 triple mutant displayed further enlargement phenotype. Overexpression of CsRAX1 or CsRAX5 gave rise to smaller leaf and thinner stem. The fruiting ability of Csrax1/2/5 plants was significantly enhanced, while that of CsRAX5 overexpression lines was greatly weakened. Similarly, cell number and free auxin level were elevated in mutant plants while decreased in overexpression lines. Biochemical data indicated that CsRAX1/5 directly promoted the expression of auxin glucosyltransferase gene CsUGT74E2. Therefore, our data suggested that CsRAXs function as repressors for leaf size development by promoting auxin glycosylation to decrease free auxin level and cell division in cucumber. Our findings provide new gene targets for cucumber breeding with increased leaf size and crop yield.

Geochemistry and geochronology of early Triassic tephra from SW China: implications for biological evolution and tectonics

ABSTRACT Late Permian to middle Triassic volcanic activities were very strong, however, volcanic records in the early Triassic strata are less reported than those of the Permo-Triassic boundary and the Triassic Olenekian-Anisian boundary in the Yangtze plate, especially within the Sichuan basin. We conduct zircon U-Pb dating and geochemical analysis of the tephra which was first found in the early Triassic Jialingjiang Formation from the Maliuping section, Hechuan, Chongqing. The volcanic ash in the paper yields the new 248.5 ± 0.7 Ma U-Pb age consistent with those of volcanic ashes in these contemporaneous strata in the Yangtze plate. Geochemical characters of whole-rock samples show lower contents in SiO2, K2O and higher components in Al2O3, CaO, MgO, relatively enriched LREE and depleted HREE with distinct negative Eu anomaly, and conspicuous Ba, Nb, Ta, Sr, P, Ti depletion and Th, U, K, Nd enrichment, which is similar to those of the Mung Bean rock of the Triassic Olenekian-Anisian boundary, and those of acidic volcanics from the Sanjiang orogenic belt and Shiwandashan-Qiangfang suture zone during the Early-Middle Triassic. Trace elements of whole rock and analysed zircons of the tuff imply its primary magma derived from Rhyodacite/Dacite and its tectonic setting of volcanic arc granite with continental crust affinity. The early Triassic volcanism during the syn-collision stage of the Paleo-Tethys evolution was less active than those of the Permo-Triassic boundary and the Triassic Olenekian-Anisian boundary, while the volcanic event may have a crucial effect on prolonging fully biotic recovery and entirely ecosystem turnover soon after the Permian-Triassic mass extinction.

Revisiting ecological carrying capacity indices for bivalve culture

Ecological carrying capacity (ECC) indices for bivalve culture rely on key ecosystem turnover rates: 1. clearance time (CT), the time needed for the cultured bivalves to filter the entire bay volume; 2. renewal time (RT), the time required to replace the entire bay volume with external water; and 3. production time (PT), the time needed for phytoplankton biomass renewal via local primary production. These turnover rates are conceptually straightforward but lack measurement standardizations in the context of ECC assessments. This study compares simple turnover rate methods with more complex approaches designed to address key assumptions and improve accuracy. Method comparisons were performed across multiple embayments (systems) in Prince Edward Island, Canada. When crop aggregation and system-scale refiltration effects were considered, CT increased by a factor of 14 to 22 depending on the system and species under cultivation. Seasonal temperature considerations further impacted CT by a factor of 38 to 142. Regarding RT, validated hydrodynamic models and tidal prism models produced remarkably different outcomes; the tidal prism approach underestimated RT by 77–94% across the studied systems. Conversely, PT was unaffected by contrasting phytoplankton parameterization; pre-aquaculture (1969–1970) and contemporary (2011−2012) datasets led to similar PT outcomes. However, other metrics revealed a contemporary shift towards low phytoplankton biomass and smaller phytoplankton cells (picophytoplankton); these observations suggest that PT provides insufficient granularity regarding microalgae biomass replacement. Overall, the study rejects a common assumption that the bay-scale turnover rates serving the conventional CT/RT and CT/PT indices can be easily and accurately parameterized; these indices should be used cautiously in assessing the sustainability of farming activities.

Magnesium Isotope Ratios Reflect the Size and Source of Mg Loss along a Glacial Retreat Chronosequence

Magnesium (Mg) stable isotope ratios reflect Mg turnover in ecosystems. At the Hailuogou glacial retreat chronosequence in SW China, about one-third of the initially present Mg was lost from the topsoil in 127 years. We determined bulk soil and exchangeable δ26Mg values at six sites exposed by the glacier from 0 to 127 years ago. Moreover, we conducted a weathering experiment (pHstat) at the youngest (0 years) and the oldest (127 years) sites and measured δ26Mg values in differently reactive pools. We found a close correlation between the δ26Mg values of the bulk topsoils (0–10 cm) and the Mg depletion rates (r = 0.98, p < 0.001, n = 5). The particularly fast Mg loss in the first 37 years was attributable to leaching of exchangeable Mg and the fast dissolution of chlorite as revealed by the lower δ26Mg values of the fast- (−1.28 ± 0.10‰) than the slow-reacting (−0.64 ± 0.11‰) pool at the 0 year-old site in our pHstat experiment. The low δ26Mg values of the fast-reacting pool matched those reported for chlorite. Our results indicate that the δ26Mg values might be used as proxy of Mg loss and to identify the mineral sources of this loss.

Rapid dissimilatory nitrate reduction to ammonium conserves bioavailable nitrogen in organic deficient soils

Large amounts of nitrogen fertilized to food production are lost via denitrification and leaching. Dissimilatory nitrate reduction to ammonium (DNRA) is a bioprocess competing with denitrification, and it conserves bioavailable nitrogen in soil ecosystems. The carbon to nitrogen (C/N) ratio has long been believed essential to balance the competition between DNRA and denitrification, but increasing evidence indicates that DNRA may occur unrelated to C/N ratio via a largely unknown mechanism. Taking Geobacter as representative bacteria, we found that the kinetic of nitrite bio-reduction to ammonium was the key to enhancing DNRA and demonstrated it in pure and mixed cultures and soil ecosystems. Compared to other two strains of DNRA bacteria, Geobacter sulfurreducens was confirmed for the first time to conduct a 3-fold more rapid DNRA (NO2−→NH4+) when it grew with the kinetically matched nitrite accumulator Delftia tsuruhatensis (NO3−→NO2−). They assisted and restricted each other to bring their population ratio close to the theoretical yield ratio of 2.7:1 while performing cross-feeding with nitrite and ammonium. This rapid DNRA was further demonstrated to conserve 2–8 times more reactive nitrogen in organic deficient soils, and up to 40% of 15NO3− was reduced to ammonium. Our results found a sustainable way of nitrogen retention in soils, and have broader implications for understanding nitrogen turnover in ecosystems.

How detritivores, plant traits and time modulate coupling of leaf versus woody litter decomposition rates across species

Abstract Plant functional traits are increasingly used to understand ecological relationships and (changing) ecosystem functions. For understanding ecosystem‐level biogeochemistry, we need to understand how (much) traits co‐vary between different plant organs across species and its implications for litter decomposition. However, we do not know how the degree of synchronous variation in decomposition rates between organs across species could be influenced by different keystone invertebrates decomposing different senesced plant organs, especially in warm‐climate forests. Here we asked whether interspecific patterns in wood and leaf decomposition rates and in the spectra of resource economics traits underpinning them, co‐vary across woody species; and how (much) the keystone invertebrate decomposers of the litter of these organs enhance or lower such co‐variation of decomposition rates through time. We addressed these questions through an 18‐month ‘common‐garden’ decomposition experiment using leaf, twig and branch litter of 41 woody species in two distant subtropical forest sites in east China. We quantified the effects of leaf, twig and branch functional traits and their respective key invertebrates (moth larvae, termites) on the decomposition rates of those organs. Interspecific variation in wood traits was partly decoupled from that in leaf traits across species, while strong coupling was found between twigs and branches. The co‐variation between leaf and woody organ decomposition rates was altered dynamically through the shifting activities of the key decomposers, which created nonlinear relationships of invertebrate litter consumption as a function of species rankings along the resource economic trait spectra of leaves and branches. The deviations from coupling of decomposition rates between organs were likely caused by combinations of three mechanisms: (1) (de‐)coupling between organs of other traits, not commonly considered in resource economics spectra (e.g. resins) (2) leaf and wood decomposers having specific diet requirements and (3) temporal patterns of the decomposers' activity. Synthesis. Our study highlights the importance of considering the different ways by which invertebrate detritivores drive decomposition processes through time. Under the ongoing biodiversity decline, future research would benefit from a better understanding of the role of the dynamic interactions between detritivore activities and plant functional traits on the carbon turnover in ecosystems.

Using the knowledge of past ecosystem turnover to inform restoration efforts: A case study from Nigeria

Using the knowledge of past ecosystem turnover to inform restoration efforts: A case study from Nigeria

Ecosystem turnover in an urbanized subtropical seascape driven by climate and pollution

Natural and anthropogenic factors shape present-day benthic marine ecosystems. Understanding their combined influence on benthic communities is limited, however, by a lack of biological monitoring. Using a conservation paleobiology approach, this study establishes biological baselines and assesses the effects of natural and anthropogenic environmental change on benthic communities in an urbanized subtropical seascape. We compared subsurface (“past”, covering approximately the last 50–100 years) and surface ("present", covering approximately the last 5 years) faunal assemblages in sediment grab samples in Hong Kong, one of the busiest ports and urbanized coastal areas in the world. Results show that both natural (climate, monsoon) and anthropogenic factors (metal pollution, damming) were associated with recent faunal changes (dissimilarities between subsurface and surface faunal assemblages). Changes in freshwater and sediment discharge from the Pearl River due to monsoon rains and dams produced a strong west-east gradient in the turnover of rare species. Pollution from metals resulted in the turnover of abundant and dominant species in the central part of Hong Kong. Examining these data in the context of published results from other urbanized coastal areas around the world suggests that metal pollution may be an important and understudied factor, responsible for benthic turnover in regions where pollution levels exceed thresholds for sediment toxicity.

Evaluating the role of coastal hypoxia on the transient expansion of microencruster intervals during the early Aptian

Worldwide, a growing number of modern coastal marine ecosystems are increasingly exposed to suboxic- or even anoxic conditions. Low seawater oxygen levels trigger significant ecosystem changes and may result in mass mortality of oxygen-sensitive biota. The applicability of observations from recent (anthropogenically influenced) suboxic coastal settings to fossil anoxic shallow-marine environments is, however, as yet poorly explored. The test case documented here are upper Barremian to lower Aptian strata in the Lusitanian Basin (Ericeira section, Portugal). These are characterized by the transient demise of rudist–coral communities and the rapid establishment of microencruster facies in the vacant ecological niches. The hypothesis is tested that the temporal expansion of the microencrusting organism Lithocodium aggregatum took place in response to platform-top seawater oxygen depletion. We critically discuss the outcome of a multi-proxy palaeoseawater redox approach (e.g. Rare Earth Elements (REEs), U isotopes and palaeoecology) and put the robustness of the proxies applied here to the test. This is done by considering issues with these methods in general but also emphasizing the significance of terrigenous contamination and fractionation effects. Data shown here document that evidence for coastal seawater oxygen depletion in the prelude of Oceanic Anoxic Event (OAE) 1a is lacking, and hence, anoxia was not the driving mechanism for the demise of rudist–coral ecosystems in the proto-North Atlantic platform setting studied here. In contrast, well-oxygenated early Aptian platform-top water masses are proposed for this site. Geologically short (decades to millennia) fluctuations in seawater oxygen levels cannot be excluded, however. But even if these took place, they offer no explanation for the Kyr to Myr-scale patterns discussed here. The present paper is relevant as it sheds light on the complexity of mechanisms that drive punctuated Early Cretaceous coral–rudist ecosystem turnover, and assess strengths and weaknesses of redox proxies applied to ancient shallow-marine platform carbonates.

Fire and hydrologically mediated diversity change in subalpine forests through the Holocene

AbstractQuestionsWe consider whether: (a) fire frequency and hydrologic trends drive changes in subalpine forest community diversity and; (b) if there are cumulative effects on diversity when frequent fire and hydrologic drying occur synchronically?LocationWe use three high elevation sites from Wyoming, USA to investigate the response and resiliency of subalpine forests in the Rocky Mountains to centennial‐to‐millennial drought and fire disturbances in regards to shifts in pollen richness, evenness and diversity.Methods‘We examine ecological changes measured by pollen richness, evenness and diversity between subalpine communities under drying and wetting conditions to determine if there is an amplified effect when differing fire frequencies are considered. Using the inverse Simpson index of pollen diversity on pollen percentages as an estimate of biodiversity.ResultsPeriods of frequent fire display significantly higher diversity (p &lt; 0.05) than periods of infrequent or intermediate fire return intervals regardless of hydrologic trends at Little Windy Hill Pond. Further, sites in the northern and southern Rocky Mountains appear to operate under differing fire regimes with sites in the northern Rocky Mountains not recording periods of frequent fire (&gt;225 year mean fire return interval) through the Holocene.ConclusionsChanges in past pollen abundance and diversity have the ability to capture past landscape structure and ecosystem turnover prior to European settlement of the Americas. If fire regimes in subalpine forests of the Rocky Mountains continue trending towards higher frequencies there is the potential for these areas to experience an increase in vegetation diversity.

Ecosystem turnover in palaeoecological records: The sensitivity of pollen and phytolith proxies to detecting vegetation change in southwestern Amazonia

Identification of ecosystem turnover in the palaeo-vegetation record is important for understanding the resilience of ecosystems to past environmental change. There is uncertainty over the ability of different types of palaeo-vegetation proxies to detect ecosystem turnover. The aim of this paper is to compare the sensitivity of two palaeo-vegetation proxies – pollen and phytoliths – to changes within and between three key tropical South American ecosystems: evergreen forest, dry forest and savannah. A quantitative approach is used to assess the sensitivity of these two proxies to vegetation changes, based on the variability of proxy assemblages from 1-ha ecological plots in ecotonal south-west Amazonia. This modern dataset of proxy variability within evergreen forest, dry forest and savannah plots is then used to define thresholds for proxy variability which differentiate floristic changes within an ecosystem from ecosystem turnover. These thresholds are applied to two palaeo-vegetation records from NE Bolivia. Our results show that pollen is more sensitive than phytoliths to changes within evergreen forest, but phytoliths are more sensitive than pollen to changes within dry forest. Both proxies were equally sensitive to changes within the savannahs. These are important considerations for palaeoecologists selecting proxies for the study of ecosystem turnover in the palaeo-record. Application of the thresholds to the palaeo-record demonstrated the utility of this quantitative approach for assessing the magnitude of vegetation change in the palaeo-record. This quantitative approach is therefore a useful tool to improve the identification of ecosystem turnover in the palaeo-record.

Mid‐elevation ecosystems of Panama: future uncertainties in light of past global climatic variability

ABSTRACTModern changes in regional climates will result in high ecosystem turnover and substantial biodiversity rearrangements. Understanding these changes requires palaeoecological studies at temporal resolutions comparable to the time window at which modern climate change is occurring. Here we present a multi‐proxy, high‐resolution record of forest and lake ecosystem change that occurred during the last 1100 years at middle elevations in Panama. From ∼900 to 1400 CE, regional forest and lake ecosystems were characterized by high seasonality, probably associated with both high El Niño activity and higher global temperatures. At ∼1400 CE, an abrupt transition marked the decoupling of forest and lake responses, with forest responding mostly to local patterns of human occupation, and lake trophic status being controlled mostly by the regional precipitation–evaporation balance, possibly associated with solar irradiance. Factors that played important roles in shaping regional ecosystems during the last 1100 years will probably again play critical roles within the coming decades, i.e. higher precipitation seasonality and higher temperatures. Past responses of the system, together with pervasive human activities, suggest that future conditions will simplify mid‐elevation forests. Given the importance of these geographical locations as hotspots of biological diversity, substantial losses of global biodiversity are foreseen.

The harbour of Elaia: A palynological archive for human environmental interactions during the last 7500 years

Abstract Elaia, the harbour city for ancient Pergamon (western Turkey), was investigated using geoarchaeological methods. The rise and fall of Elaia were closely linked to the flourishing period of Pergamon, which ruled wide parts of today's western Turkey in Hellenistic times. In the framework of this research, the palynological analysis of a 9 m sediment core, Ela-70, retrieved from the enclosed harbour of the city, was carried out to reconstruct the vegetation and environmental history of the wider Gulf of Elaia region. An age-depth model, based on 11 calibrated radiocarbon ages, starting from 7.5 ka BP, provides the basis for the high resolution study of sediments from the Hellenistic period, as well as before and after. The lower part of the pollen diagram is characterised by high percentages of deciduous oaks and pines, suggesting the dominance of open forests close to the coring site. The change from oak forests to a cultural landscape, with olive, pistachio, walnut, and grape, started around 850 BC, reaching a maximum ca. 250 BC, and continuing to ca. AD 800. This period is characterised by increase of fire activity, soil erosion intensity, and pastoral farming. Such long-lasting intensive land use likely led to the climax ecosystem turnover from open deciduous oak forests to pine stands, while salt marshes developed around the coring site. The discovery of the dinoflagellate cysts of Peridinium ponticum , a Black Sea endemic species, in the harbour of Elaia evidences maritime trade between the Aegean Sea and the Black Sea; its first occurrence coincides with the time of the Mithridatic Wars (1st century BC). In conclusion, palynological data, in addition to historical and archaeological records, provide a deeper insight into human environmental interactions, as derived from the geoarchaeological archive of the harbour of Elaia.

Species richness and biomass explain spatial turnover in ecosystem functioning across tropical and temperate ecosystems.

Predicting ecosystem functioning at large spatial scales rests on our ability to scale up from local plots to landscapes, but this is highly contingent on our understanding of how functioning varies through space. Such an understanding has been hampered by a strong experimental focus of biodiversity-ecosystem functioning research restricted to small spatial scales. To address this limitation, we investigate the drivers of spatial variation in multitrophic energy flux-a measure of ecosystem functioning in complex communities-at the landscape scale. We use a structural equation modelling framework based on distance matrices to test how spatial and environmental distances drive variation in community energy flux via four mechanisms: species composition, species richness, niche complementarity and biomass. We found that in both a tropical and a temperate study region, geographical and environmental distance indirectly influence species richness and biomass, with clear evidence that these are the dominant mechanisms explaining variability in community energy flux over spatial and environmental gradients. Our results reveal that species composition and trait variability may become redundant in predicting ecosystem functioning at the landscape scale. Instead, we demonstrate that species richness and total biomass may best predict rates of ecosystem functioning at larger spatial scales.

Advances in experimental methods for root system architecture and root development

Plant roots play important roles in acquisition of water and nutrients, storage, anchoring, transport, and symbiosis with soil microorganisms, thus quantitative researches on root developmental processes are essential to understand root functions and root turnover in ecosystems, and at the same time such researches are the most difficult because roots are hidden underground. Therefore, how to investigate efficiently root functions and root dynamics is the core aspect in underground ecology. In this article, we reviewed some experimental methods used in root researches on root development and root system architecture, and summarized the advantages and shortages of these methods. Based on the analyses, we proposed three new ways to more understand root processes: (1) new experimental materials for root development; (2) a new observatory system comprised of multiple components, including many observatory windows installed in field, analysis software, and automatic data transport devices; (3) new techniques used to analyze quantitatively functional roots.

Compensatory feeding and low nutrient assimilation efficiencies lead to high nutrient turnover in nitrogen-limited snails

According to stoichiometric principles, the ratios at which consumers recycle nutrients depend on the elemental compositions of the consumer and its food. However, nutrient assimilation efficiencies and ingestion rates can vary among consumer species and, thus, can affect the rates of consumer-mediated nutrient recycling (CNR). The grazer Theodoxus fluviatilis has high nutrient excretion rates of either P or N, depending on grazer growth limitation, and has a high body N. I examined how a grazer with a high proportion of N in its body tissues can assimilate enough N to maintain that N content despite high N excretion rates by estimating the mass balance for nutrient recycling including nutrient excretion through fecal pellets. I used the snail species Theodoxus fluviatilis and Lymnea peregra fed nutrient-enriched periphyton in a 2-d grazing experiment done in 48 experimental units. I estimated periphyton and grazer nutrient stoichiometry and nutrient excretion rates and ratios in dissolved and fecal-pellet form, and calculated nutrient assimilation efficiencies of the limiting nutrient (N). Theodoxus fluviatilis had higher N excretion rates, lower N assimilation efficiency, and higher ingestion rates than L. peregra. Thus, T. fluviatilis recycled more N by ingesting and processing a larger amount of food per unit time than L. peregra. My study shows that grazers with low nutrient assimilation efficiencies and high nutrient demands can assimilate sufficient nutrients via high ingestion rates. The consequence of this strategy (high ingestion and excretion rates) could be a more rapid nutrient turnover in ecosystems dominated by these grazers.

Climate change impacts on zooplankton and benthic communities in Lake Unterer Giglachsee (Niedere Tauern Alps, Austria)

AbstractWe examined a sediment core from a climatically sensitive High Alpine lake Unterer Giglachsee in the Niedere Tauern Alps in Austria. Our aim was to investigate long‐term climate change impacts on aquatic invertebrates (Chironomidae, Cladocera) with a special focus on the ending of the Little Ice Age and the present climate warming. Although the changes in faunal assemblages were relatively subtle through the sedimentary record, a mutual faunal breakpoint at ∼1900 AD was distinguished. In addition, the faunal dynamics correlated closely with instrumental Alpine temperature records and with reconstructed Northern Hemisphere climate development over the examined time period. In particular, significant relationships between relative taxa abundance and temperature were found with chironomids Sergentia, Paracladius, Paratanytarsus austriacus‐type, Cricotopus (I.) intersectus‐type, and Cricotopus cylindraceus‐type and with cladocerans Daphnia and Alonella excisa. Our results also suggested that the most recent assemblages represent unique community compositions. We conclude that our study lake is sensitive to climate warming and the composition of the aquatic ecosystem in Unterer Giglachsee has changed due to the impact of increasing temperatures. We predict that the further increasing temperatures will have direct but also cascading effects on the sensitive lake, potentially causing an ecosystem turnover where the key taxon Paracladius may play an important role.

Evidence for atmospheric carbon injection during the end-Permian extinction

The end-Permian mass extinction is marked by pronounced terrestrial ecosystem turnover and a severe loss of marine invertebrate biodiversity. This extinction event is accompanied by a prominent negative carbon-isotope excursion indicating massive changes in the global carbon cycle across the Permian-Triassic boundary. In this study, we present organic carbon-isotope data from land plant cuticles, fossil wood fragments, and bulk organic matter recovered from the Amb section in the Salt Range, Pakistan. We apply δ 13 C data from cuticles as a proxy record for the carbon-isotope composition of atmospheric CO 2 across the Permian-Triassic boundary. The data show an ∼5.5‰ negative excursion in terrestrial organic matter, reflecting the change in carbon-isotope composition of atmospheric CO 2 . Our data demonstrate that these atmospheric changes coincide with biotic (mass extinction) and abiotic (carbonate carbon-isotope perturbation) changes in the marine realm, hence affecting the entire ocean-atmosphere system.

Palaeoenvironmental shifts drove the adaptive radiation of a noctuid stemborer tribe (Lepidoptera, Noctuidae, Apameini) in the miocene.

Between the late Oligocene and the early Miocene, climatic changes have shattered the faunal and floral communities and drove the apparition of new ecological niches. Grassland biomes began to supplant forestlands, thus favouring a large-scale ecosystem turnover. The independent adaptive radiations of several mammal lineages through the evolution of key innovations are classic examples of these changes. However, little is known concerning the evolutionary history of other herbivorous groups in relation with this modified environment. It is especially the case in phytophagous insect communities, which have been rarely studied in this context despite their ecological importance. Here, we investigate the phylogenetic and evolutionary patterns of grass-specialist moths from the species-rich tribe Apameini (Lepidoptera, Noctuidae). The molecular dating analyses carried out over the corresponding phylogenetic framework reveal an origin around 29 million years ago for the Apameini. Ancestral state reconstructions indicate (i) a potential Palaearctic origin of the tribe Apameini associated with a major dispersal event in Afrotropics for the subtribe Sesamiina; (ii) a recent colonization from Palaearctic of the New World and Oriental regions by several independent lineages; and (iii) an ancestral association of the tribe Apameini over grasses (Poaceae). Diversification analyses indicate that diversification rates have not remained constant during the evolution of the group, as underlined by a significant shift in diversification rates during the early Miocene. Interestingly, this age estimate is congruent with the development of grasslands at this time. Rather than clade ages, variations in diversification rates among genera better explain the current differences in species diversity. Our results underpin a potential adaptive radiation of these phytophagous moths with the family Poaceae in relation with the major environmental shifts that have occurred in the Miocene.

Acceleration of vegetation turnover and element cycling by mammalian herbivory in riparian ecosystems

Summary 1 We examined the effects of browsing by moose and snowshoe hares on vegetation structure, species composition, plant demography and element cycling in 25 riparian (willow) vegetation stands along the Tanana River, interior Alaska, across a 250-km gradient that represented a fivefold range in moose densities (0.2–1.0 km−2). 2 Browsing frequency was much greater in areas with high moose densities. The combined browsing pressure (% of annual browse production consumed by herbivores) of moose (Alces alces) and snowshoe hares (Lepus americanus) on forage species was over fivefold greater in the high moose density areas (33%) than the low moose density areas (6%), reflecting the fivefold difference in moose densities. 3 Above-ground biomass of preferred willow species was lower in high moose density areas, and the age structure of the vegetation was significantly skewed towards younger age classes. This shift in age structure was accompanied by higher proportion of dead to live ramets, indicating higher mortality under increased browsing pressure. Increasing browsing pressure favoured later-successional species (Alnus tenuifolia and Populus balsamifera) on the landscape, as shown by both a reduction in the number and size of willow stands in high-density areas. 4 High rates of fecal input resulted in a doubling of above-ground N input in high moose density areas. The rates of carbon and nitrogen input from willow communities to the soil as mediated by moose herbivory were approximately fivefold and eightfold greater in high moose density areas than in low moose density areas, respectively. 5 Synthesis. The effects of herbivory were manifested at several ecological hierarchies, including the individual, the community, and the landscape. Across these spatial scales herbivory appears to accelerate the ecosystem turnover of carbon and nitrogen by a combination of both plant- and animal-based processes.