Fundamental research questions in subterranean biology

Five decades ago, a landmark paper inSciencetitledThe Cave Environmentheralded caves as ideal natural experimental laboratories in which to develop and address general questions in geology, ecology, biogeography, and evolutionary biology. Although the 'caves as laboratory' paradigm has since been advocated by subterranean biologists, there are few examples of studies that successfully translated their results into general principles. The contemporary era of big data, modelling tools, and revolutionary advances in genetics and (meta)genomics provides an opportunity to revisit unresolved questions and challenges, as well as examine promising new avenues of research in subterranean biology. Accordingly, we have developed a roadmap to guide future research endeavours in subterranean biology by adapting a well-established methodology of 'horizon scanning' to identify the highest priority research questions across six subject areas. Based on the expert opinion of 30 scientists from around the globe with complementary expertise and of different academic ages, we assembled an initial list of 258 fundamental questions concentrating on macroecology and microbial ecology, adaptation, evolution, and conservation. Subsequently, through online surveys, 130 subterranean biologists with various backgrounds assisted us in reducing our list to 50 top-priority questions. These research questions are broad in scope and ready to be addressed in the next decade. We believe this exercise will stimulate research towards a deeper understanding of subterranean biology and foster hypothesis-driven studies likely to resonate broadly from the traditional boundaries of this field.Peer reviewe

A conservation roadmap for the subterranean biome

The 15th UN Convention on Biological Diversity (CBD) (COP15) will be held in Kunming, China in October 2021. Historically, CBDs and other multilateral treaties have either alluded to or entirely overlooked the subterranean biome. A multilateral effort to robustly examine, monitor, and incorporate the subterranean biome into future conservation targets will enable the CBD to further improve the ecological effectiveness of protected areas by including groundwater resources, subterranean ecosystem services, and the profoundly endemic subsurface biodiversity. To this end, we proffer a conservation roadmap that embodies five conceptual areas: (1) science gaps and data management needs; (2) anthropogenic stressors; (3) socioeconomic analysis and conflict resolution; (4) environmental education; and (5) national policies and multilateral agreements.Peer reviewe

Establishing Baseline Data on Seasonal Physiological Requirements for Gammarus troglophilus in Relation to Microbial Oxygen Demand

Report issued on: 25 June 2003INHS Technical Report prepared for IDNR Division of Natural Heritag

Experimental Detritus Manipulations Unite Surface and Cave Stream Ecosystems Along a Common Energy Gradient

Subsidies of detritus from donor habitats are important energy sources for many ecosystems, but understanding their role in structuring recipient food webs requires comparative experimental studies along the full spectrum of detrital fluxes. Here we report results from an experimental addition of maize (Zea mays L.) litter to a detritus-poor cave stream ecosystem, which we then compare with analogous, past experiments using detritus-rich surface stream ecosystems that similarly have detritus-based food webs and extremely low in situ primary production. Bulk-tissue and compound-specific stable isotope analyses showed that maize litter carbon (C) was rapidly assimilated by microbes and transferred via successive trophic levels to the top of the cave stream food web (omnivorous crayfishes and predatory salamanders). All trophic levels increased in abundance and biomass, but only facultative cave taxa, that is those also found in surface streams, contributed to this numerical response. The lack of response by obligate cave species presumably occurred because evolutionary trade-offs associated with adaptations to low-C environments constrained their population-level responses during the one-year period of the litter addition. Comparison of the responses of the cave community with the analogous litter manipulation experiments in surface streams showed strong convergence in the functional relationship between invertebrate and detritus biomass (R 2 = 0.72, P \u3c 0.0001). Our results suggest that these seemingly disparate stream food webs lie along a single, common gradient of detritus supply, occupied at its extreme minimum by communities of obligate cave taxa adapted to low-energy environments

The influence of energy availability on population-, community-, and ecosystem-level processes in cave stream ecosystems

Detritus from surface environments supplies the energy that shapes community structure and fuels productivity in most cave ecosystems. However, only qualitative descriptions of cave energy dynamics are available, hindering development of quantitative models describing how energy availability influences cave ecosystem processes. In contrast, the importance of detritus for surface ecosystem processes has been appreciated for decades. This dissertation begins to close this knowledge gap by exploring how energy availability shapes cave stream ecosystem processes at multiple organizational levels (ecosystem-, community-, population-level) and time scales (evolutionary vs. ecological). Chapter Two examined potential correlations between litter breakdown rates and detrital storage, but found no such relationships among four cave streams. However, surface-adapted species dominated macroinvertebrate biomass, suggesting that surface-adapted taxa can have a significant influence on cave ecosystem processes. In Chapter Three, a whole-reach litter amendment was conducted to explore the influence of enhanced detrital inputs on cave community structure and energy flow. While the litter amendment significantly increased total consumer biomass via assimilation of amended corn-litter, the response was dictated by evolutionary history. Biomass of surface-adapted taxa increased significantly following the amendment, while biomass of obligate cave species remained unchanged. As in Chapter Two, consumer biomass was dominated by surface-adapted taxa, reinforcing their role in cave ecosystem processes relative to cave-adapted taxa, the traditional focus of cave studies. Chapters Four and Five utilized a 5+-year mark-recapture data set on the cave-adapted crayfish Orconectes australis to explore how energy availability has shaped its evolutionary history and population dynamics. Time-to-maturity, age-at-first-reproduction, and longevity of O. australis were substantially longer than those estimated for most crayfish species, indicating evolution of a K-selected life history. Chapter Five found that biomass and secondary production of O. australis were positively related to resource availability. Energetic models indicated resource deficits were not present, but that nearly all prey production is necessary to support each O. australis population. Thus, inter- and intra-specific competition for resources within caves is likely high. Collectively, Chapters Four and Five provide the first quantitative explanation of why K-selected life histories are an evolutionary advantage to obligate cave taxa like O. australis. (Published By University of Alabama Libraries

Impacts of detritivore diversity loss on instream decomposition are greatest in the tropics

It is unclear whether stream detritivore diversity enhances decomposition across climates. Here the authors manipulate litter diversity and examine detritivore assemblages in a globally distributed stream litterbag experiment, finding a positive diversity-decomposition relationship stronger in tropical streams, where detritivore diversity is lower

Impacts of detritivore diversity loss on instream decomposition are greatest in the tropics

The relationship between detritivore diversity and decomposition can provide information on how biogeochemical cycles are affected by ongoing rates of extinction, but such evidence has come mostly from local studies and microcosm experiments. We conducted a globally distributed experiment (38 streams across 23 countries in 6 continents) using standardised methods to test the hypothesis that detritivore diversity enhances litter decomposition in streams, to establish the role of other characteristics of detritivore assemblages (abundance, biomass and body size), and to determine how patterns vary across realms, biomes and climates. We observed a positive relationship between diversity and decomposition, strongest in tropical areas, and a key role of abundance and biomass at higher latitudes. Our results suggest that litter decomposition might be altered by detritivore extinctions, particularly in tropical areas, where detritivore diversity is already relatively low and some environmental stressors particularly prevalent