Biomass is a common, universal indicator of ecosystem productivity for exploring biodiversity–ecosystem functioning (BEF) relationships in all types of ecosystems. However, positive BEF is often missing in aquatic consumer communities with multitrophic interactions. Here, we apply a new indicator, integrated trophic position (iTP), which is defined as the summed TPs of all consumers weighed by the relative biomass of each taxon, for multitrophic systems to test the vertical diversity hypothesis (VDH) that functional diversity can enhance trophic energy flows within a food web. Using a meta-community of coastal benthic macroinvertebrates, we demonstrate that iTP increases in more diverse communities, supporting the VDH. Comparing our results with previous findings that stream benthic macroinvertebrates exhibit a negative BEF in contrast to the VDH, we discuss a possible mechanism to explain this contrasting pattern. Finally, we use a size-based food web approach to deepen our mechanistic understanding of the observed BEF.

Ecologists have proposed that montane grassland-shola (stunted evergreen forest) mosaics in the Western Ghats may represent alternative stable vegetation states. But paleoecology investigations seldom consider this framework, especially the role of short-term disturbances (fire, intense drought) other than long-term climatic changes, that can cause vegetation switches in landscapes with alternative vegetation states. The Sandynallah valley that hosts one of the oldest peat accumulations in the world at >50 kyr has been central to the reconstruction of paleovegetation in the montane Nilgiris, Western Ghats. Although the peat-forming vegetation here (dominated by sedges) is a unique vegetation state, its contribution to the paleovegetation signal has not been explicitly considered. We propose a conceptual framework of a tri-stability landscape with sedgeland on the valley floor, grassland on the hill slopes and shola vegetation in the boundary between sedgeland and grassland. While frost prevents shola saplings from establishing in grassland, waterlogging provides a barrier for their establishment in sedgeland, thus maintaining these distinct vegetation states under the same climate. We investigated the stable carbon isotope signatures of the cellulose fraction from two well-dated peat cores (Cores 1 and 2) collected from ~170m apart in the Sandynallah valley within the alternative stable states framework. We find that Core 1, which is closer to the boundary of valley and hill slope, shows dynamic switches between sedgeland and shola whereas Core 2, located in the centre of the valley floor, represents a stable sedgeland state. The vegetation switches and maintenance mechanisms at Core 1 is connected to a disturbance (fire) and to changing climate while Core 2 seems to be responding primarily to climatic changes. The simultaneously distinctive vegetation states in Cores 1 and 2 at such close proximity within the same valley is the first record of alternative stables states in the past in the Western Ghats.

The Sandynallah valley (Western Ghats, India) features one of the oldest peat accumulations in the world at >50 kyr and has been central to the reconstruction of late Quaternary paleoclimate using paleovegetation changes in the forest-grassland vegetation mosaic that coexist here. It is well-known that short-term disturbances (fire, frost, intense drought) can also cause vegetation switches when multiple stable states exist, but this framework has seldom been considered in paleoecology investigations. Using stable carbon isotope signatures (relative C3-C4 vegetation abundance) on the cellulose fraction from two well-dated peat cores ~170 m apart - Core 1 closer to the hillslope (32000 years old) and Core 2 from the centre of the valley floor (45,000 years old) - we looked at paleovegetation changes and the implications for paleoclimate reconstruction within the alternative stable states framework. Charcoal data from another sediment profile from the same valley was used to correlate with paleofires. We propose that the valley floor is bistable, switching between peat-forming vegetation ‘sedgeland’ and montane stunted evergreen forest ‘shola’, maintained by level of waterlogging. Core 1 shows shola-sedgeland dynamics with vegetation switching at c.22ka from shola (possibly due to fires) to a prolonged unstable state until 13 ka sustained by low waterlogging. Following a hiatus c.13-7 ka, sedgeland dominates, with a shift into shola at 3.75 ka driven by increasing aridity. Core 2 shows a relatively stable signature, enriched in C3-vegetation in the last glacial (45-20 ka) compared to the Holocene. Given temperature is the primary driver of abundance in C3-C4 mixed-grasslands, C4 dominance beginning c.18.5 ka followed by C4 enrichment is indicative of deglacial warming that continues into the Holocene except for a departure at ~10 ka. The record at Core 2 is indicative of changing climate while Core 1 shows disturbance-based vegetation dynamics. The simultaneously distinctive vegetation states in Cores 1 and 2 within the same valley is the first record of alternative stable states in the past in the montane tropics. Our results point to the need to account for short-term disturbances and site attributes before ascribing vegetation changes to changing climate in alternative stable states landscapes.

Long-distance migrations by marine fish have long fascinated scientists, but are difficult to track by visual surveys. Here, we propose a new method to easily and precisely track such migrations using stable nitrogen isotopic composition at the base of the food web (δ15NBase), which can be estimated by using compound-specific isotope analysis. δ15NBase exclusively reflects the δ15N of nitrate in the ocean at a regional scale and is not affected by the trophic position of sampled organisms. We initially constructed a δ15NBase isoscape in the northern North Pacific, and determined retrospective δ15NBase values of chum salmon (Oncorhynchus keta) from their vertebral centra. Then, we estimated the migration routes of chum salmon during their skeletal growth by using a state-space model. Our isotope tracking method successfully reproduced a known chum salmon migration route between the Okhotsk and Bering seas, and indicates the presence of a novel migration route to the eastern Bering Sea Shelf during a later growth stage.