Geographically variable biotic interactions and implications for species ranges

The challenge Understanding how biotic interactions affect species' geographical ranges, biodiversity patterns and ecological responses to environmental change is one of the most pressing challenges in macroecology. Extensive efforts are underway to detect signals of biotic interactions in macroecological data. However, efforts are limited by bias in the taxa and spatial scale for which occurrence data are available and by difficulty in ascribing causality to co-occurrence patterns. Moreover, we are not necessarily looking in the right places; analyses are largely ad hoc, depending on availability of data, rather than focusing on regions, taxa, ecosystems or interaction types where biotic interactions might affect species' geographical ranges most strongly. Unpicking biotic interactions We suggest that macroecology would benefit from the recognition that abiotic conditions alter two key components of biotic interaction strength: frequency and intensity. We outline how and why variation in biotic interaction strength occurs, explore the implications for species' geographical ranges and discuss the challenges inherent in quantifying these effects. In addition, we explore the role of behavioural flexibility in mediating biotic interactions potentially to mitigate impacts of environmental change. New data We argue that macroecology should take advantage of "independent" data on the strength of biotic interactions measured by other disciplines, in order to capture a far wider array of taxa, locations and interaction types than are typically studied in macroecology. Data on biotic interactions are readily available from community, disease, microbial and parasite ecology, evolution, palaeontology, invasion biology and agriculture, but most are yet to be exploited within macroecology. Integrating biotic interaction strength data into macroecology Harmonization of data across interdisciplinary sources, taxa and interaction types could be achieved by breaking down interactions into elements that contribute to frequency and intensity. This would allow quantitative biotic interaction data to be incorporated directly into models of species distributions and macroecological patterns

Protection efforts have resulted in ~10% of existing fish biomass on coral reefs

The amount of ocean protected from fishing and other human impacts has often been used as a metric of conservation progress. However, protection efforts have highly variable outcomes that depend on local conditions, which makes it difficult to quantify what coral reef protection efforts to date have actually achieved at a global scale. Here, we develop a predictive model of how local conditions influence conservation outcomes on ~2,600 coral reef sites across 44 ecoregions, which we used to quantify how much more fish biomass there is on coral reefs compared to a modeled scenario with no protection. Under the assumptions of our model, our study reveals that without existing protection efforts there would be ~10% less fish biomass on coral reefs. Thus, we estimate that coral reef protection efforts have led to approximately 1 in every 10 kg of existing fish biomass

Wave exposure reduces herbivory in post-disturbed reefs by fltering species composition, abundance and behaviour of key fsh herbivores

Este artículo contiene 14 páginas, 6 figuras, 3 tablas.Harsh environmental conditions limit how species use the landscape, strongly infuencing the way assemblages are distributed. In the wake of repeated coral bleaching mortalities in Lakshadweep, we examined how wave exposure infuences herbivory in exposed and sheltered reefs. We used a combination of i. feld observations of fsh herbivore composition, abundance and activity across 6 exposed and 6 sheltered reefs; ii. experimental manipulations in a subset of these reefs (herbivore exclosures); and iii. opportunistic observations of fsh recruitment, to determine how exposure infuences herbivore biomass and herbivory. Species richness, biomass, abundance, total bite rates and species-specifc per capita bite rates were lower in exposed compared to sheltered reefs, linked to strong environmental fltering of species composition, abundance and behaviour. For some critical species, this environmental fltering begins with diferential recruitment and post-recruitment processes between exposures. Bite rates at sheltered sites were dominated by just a few species, most being laterally compressed surgeonfsh that may fnd it difcult accessing or surviving in wave-battered shallow reefs. Exclosure experiments confrmed that exposed reefs were less controlled by herbivores than sheltered reefs. In post-disturbed reefs like Lakshadweep, environmental gradients appear to be key mediators of critical functions like herbivory by determining species composition, abundance and behaviour.This work was funded by Rohini Nilekani Philanthropies (RA, SY, TA, PR), DSTSERB Intramural Grant (EMR/2017/004014), Azim Premji University Research Grant, DBT-RA Fellowship Program in Biotechnology and Life Sciences (RK) and the Spanish Consejo Superior de Investigaciones Científicas under the project supported by the Memorandum of Understanding between CEAB (CSIC)- NCF, Department of Science and Technology and IdeaWild. This research was conducted under permit F.No.16/11/2014-ADM of the Administration and the Department of Science and Technology, Union Territory of Lakshadweep.Peer reviewe

Hypothesizing novel mating behaviours in the squaretail grouper based on direct behavioural observations

Historically unfished, high-density spawning aggregations are vanishingly uncommon. Behavioural observations from such aggregations are rare, and may be sometimes novel and unexpected. Given the weight of evidence required to document spawning aggregations, how can we best report rare and unusual behavioural variations in spawning populations? Based on two years of in-water observations of a high-density spawning aggregation of the squaretail grouper in the Lakshadweep Archipelago, we described a previously unreported male alternative reproductive tactic (ART) and an inverse size assortment with large males courting several small females that shoaled mid-water (https://doi.org/10.1186/s12898-017-0120-5). In critiquing our manuscript, it has been suggested that our observations, methodologies and interpretation are inadequate, flawed, and do not fit within currently accepted theory (https://doi.org/10.1186/s12898-018-0206-8). While offering a detailed counter of the main methodological and theoretical criticisms we question how best to document and interpret novel behaviours in poorly known systems. Reporting novelty itself can hardly be the basis of criticism. Our report relied on direct in-water observations, conducted at peak densities over two spawning years. The critique ignores this, choosing instead to focus on a supplementary video which was not the basis of our conclusions. Like other researchers working on this species, we did not directly observe mating, but report courtship as a well-established proxy used across mating systems studies. Apart from these methodological concerns, the authors suggest that there is no theoretical support for our observations. However, sexual selection theory provides well-established frameworks showing that, at very high mating densities, a variety of tactics can emerge, that often vary considerably between populations and locations. In our original paper, we use this broader theory of sexual selection together with detailed behavioural data to propose plausible evolutionary explanations that bear testing in these novel, high-density systems. We agree with the authors that novel observations should be scrutinised carefully as they can challenge our current understanding of the range of behaviours populations display and serve as a springboard for theoretical advancement. Given their rarity, these observations should be evaluated against the rigour of their documentation and the transparency of their reporting. In this context, we hope our carefully documented observations serve as a useful addition to the fascinating and complex natural history of species like the squaretail grouper

Coping with catastrophe: foraging plasticity enables a benthic predator to survive in rapidly degrading coral reefs

10 páginas, 7 figuras, 1 tabla, 1 apéndice.Human-induced rapid environmental change (HIREC) disproportionately affects species with specialist traits and long generation times. By circumventing prolonged evolutionary processes, behavioural plasticity is critical in allowing species to cope with rapid environmental changes within their lifetimes. Coral reefs have faced multiple mass mortality events of corals related to climate change in the last two decades. The consequent loss of structural complexity adversely impacts long-lived, structure-dependent fish predators. We attempted to determine how well a guild of groupers (Pisces: Epinephelidae) copes with rapid structural change in the lightly fished Lakshadweep Archipelago, Indian Ocean. Of the 15 species, territorial and site-attached groupers declined exponentially with decreasing structural complexity, while widely ranging species showed no change. However, one site-attached species, the peacock grouper, Cephalopholis argus, maintained high densities across the structural gradient. We explored the mechanisms this species employs to cope with declining habitat structure. Our observations indicate that both a potential release from specialist competitors and plasticity in foraging behaviour (foraging territory size, diet and foraging mode) appeared to favour the peacock grouper's survival in sites of high and low structure. While specialist competitors dropped out of the assemblage, the foraging territory size of peacock groupers increased exponentially with structural decline, but remained constant and compact (50 m2) above a threshold of structural complexity (corresponding to a canopy height of 60 cm). Interestingly, despite significant differences in prey density in sites of high and low structure, gut content and stable isotope analyses indicated that peacock groupers maintained a specialized dietary niche. In-water behavioural observations suggested that diet specialization was maintained by switching foraging modes from a structure-dependent ‘ambush’ to a structure-independent ‘widely foraging’ mode. The remarkable foraging plasticity of species such as the peacock grouper will become increasingly critical in separating winners from losers and may help preserve specialist ecosystem functions as habitats collapse as a result of climate change.This study was conducted with funding from Rufford Small Grants Foundation (grant number 16133-B) and the Pew Marine Fellowship.Peer reviewe

Data from: Long-lived groupers require structurally stable reefs in the face of repeated climate change disturbances

Benthic recovery from climate-related disturbances does not always warrant a commensurate functional recovery for reef-associated fish communities. Here, we examine the distribution of benthic groupers (family Serranidae) in coral reef communities from the Lakshadweep archipelago (Arabian Sea) in response to structural complexity and long-term habitat stability. These coral reefs that have been subject to two major El Niño Southern Oscillation-related coral bleaching events in the last decades (1998 and 2010). First, we employ a long-term (12-yr) benthic-monitoring dataset to track habitat structural stability at twelve reef sites in the archipelago. Structural stability of reefs was strongly driven by exposure to monsoon storms and depth, which made deeper and more sheltered reefs on the eastern aspect more stable than the more exposed (western) and shallower reefs. We surveyed groupers (species richness, abundance, biomass) in 60 sites across the entire archipelago, representing both exposures and depths. Sites were selected along a gradient of structural complexity from very low to high. Grouper biomass appeared to vary with habitat stability with significant differences between depth and exposure; sheltered deep reefs had a higher grouper biomass than either sheltered shallow or exposed (deep and shallow) reefs. Species richness and abundance showed similar (though not significant) trends. More interestingly, average grouper biomass increased exponentially with structural complexity, but only at the sheltered deep (high stability) sites, despite the availability of recovered structure at exposed deep and shallow sites (lower-stability sites). This trend was especially pronounced for long-lived groupers (life span >10 yrs). These results suggest that long-lived groupers may prefer temporally stable reefs, independent of the local availability of habitat structure. In reefs subject to repeated disturbances, the presence of structurally stable reefs may be critical as refuges for functionally important, long-lived species like groupers

Data from: Alternative reproductive tactics and inverse size-assortment in a high-density fish spawning aggregation

Background: At high densities, terrestrial and marine species often employ alternate reproductive tactics (ARTs) to maximize reproductive benefits. We describe ARTs in a high-density and unfished spawning aggregation of the squaretail grouper (Plectropomus areolatus) in Lakshadweep, India. Results: As previously reported for this species, territorial males engage in pair-courtship, which is associated with a pair-spawning tactic. Here, we document a previously unreported school-courtship tactic; where territorial males court multiple females in mid-water schools, which appears to culminate in a unique ‘school-spawning’ tactic. Courtship tactics were conditional on body size, local mate density and habitat, likely associated with changing trade-offs between potential mating opportunities and intra-sexual competition. Counter-intuitively, the aggregation showed a habitat-specific inverse size-assortment: large males courted small females on the reef slope while small males courted equal-sized or larger females on the shelf. These patterns remained stable across two years of observation at high, unfished densities. Conclusions: These unique density-dependent behaviours may disappear from this aggregation as overall densities decline due to increasing commercial fishing pressure, with potentially large consequences for demographics and fitness