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Evidence of sodium limitation in ants and termites in a Neotropical savanna

Published online by Cambridge University Press:  07 January 2022

Natalie A. Clay*
Affiliation:
School of Biological Sciences, Louisiana Tech University, Ruston, LA71272, U.S.A
Donald B. Shepard
Affiliation:
School of Biological Sciences, Louisiana Tech University, Ruston, LA71272, U.S.A
Adrian A. Garda
Affiliation:
Department of Botany and Zoology, Federal University of Rio Grande do Norte, Natal, Brazil
Daniel O. Mesquita
Affiliation:
Department of Systematics and Ecology, Federal University of Paraíba, João Pessoa, Brazil
Alexandre Vasconcellos
Affiliation:
Department of Systematics and Ecology, Federal University of Paraíba, João Pessoa, Brazil
*
Author for correspondence: Natalie A. Clay, Email: [email protected]

Abstract

Nutritional ecology of ropical ecosystems like Neotropical savannas, which are of high conservation concern, is understudied. Sodium is essential for heterotrophs but availability often falls short relative to plant consumer requirements. Savanna plant consumers like ants and termites should be sodium-limited due to high temperatures, nutrient-poor soils, and lack of oceanic sodium deposition. We tested the hypothesis that Neotropical savanna ants and termites are sodium-limited. Termites were tested by supplementing 0.25 m2 plots with H2O (control), 0.1%, 0.5%, or 1.0% NaCl and measuring termite presence and artificial substrate mass loss after 1 week. Ants were tested by collecting ants that recruited to H2O (control), 0.1%, 0.5%, and 1.0% NaCl and 1.0%, 10%, and 20% sugar baits on paired diurnal–nocturnal transects. Termites were 16 times more likely to occur on 1% NaCl than H2O plots and wood-feeding termites were most frequent. However, the decomposition rate did not differ among treatments. Ant bait use increased with increasing NaCl concentration and 1% NaCl usage was similar to sugar bait usage. Ants were 3.7 times more active nocturnally than diurnally, but contrary to predictions bait type (water, sugar or NaCl) usage did not differ between day and night. Together, these results provide strong evidence of sodium limitation in Neotropical savannas.

Type
Research Article
Copyright
© The Author(s), 2022. Published by Cambridge University Press

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References

Ab’Saber, AN (1983) O dominio dos Cerrados: introduçao ao conhecimento. Revista do Servidor Publico 111, 4155.Google Scholar
Addo-Bediako, A, Chown, SL, and Gaston, KJ (2001) Revisiting water loss in insects: a large scale view. Journal of Insect Physiology 47, 13771388.CrossRefGoogle ScholarPubMed
Albrecht, M and Gotelli, NJ (2001) Spatial and temporal niche partitioning in grassland ants. Oecologia 126, 134141. doi: 10.1007/s004420000494 CrossRefGoogle ScholarPubMed
Alencar, A, Shimbo, J Z, Lenti, F, Marques, CB, Zimbres, B, Rosa, M, Arruda, V, Castro, I, Ribeiro, JPFM, Varela, V, Alencar, I, Piontekowski, V, Ribeiro, V, Bustamante, MMC, Sano, EE and Barroso, M (2020) Mapping three decades of changes in the Brazilian savanna native vegetation using Landsat data processed in the google earth engine platform. Remote Sensing 12, 924. doi: 10.3390/rs12060924.CrossRefGoogle Scholar
Angilletta, MJ (2009) Thermal adaptation: a theoretical and empirical synthesis. Oxford University Press, Oxford, UK.CrossRefGoogle Scholar
Aumann, G and Emlen, J (1965) Relation of population density to sodium availability and sodium selection by microtine rodents. Nature 208, 198199.CrossRefGoogle ScholarPubMed
Berzaghi, F, Verbeeck, H, Nielsen, MR, Doughty, CE, Bretagnolle, F, Marchetti, M and Scarascia-Mugnozza, G (2018) Assessing the role of megafauna in tropical forest ecosystems and biogeochemical cycles – the potential of vegetation models. Ecography 41, 19341954.CrossRefGoogle Scholar
Bignell, DE and Eggleton, P (2000) Termites in ecosystems. In Abe, T, Bignell, DE, & Higashi, M (Eds.), Termites: Evolution, Sociality, Symbioses, Ecology (pp. 363387). Dordrecht: Kluwer Academic Publishers.CrossRefGoogle Scholar
Bolton, B (1994) Identification Guide to the Ant Genera of the World. Cambridge, USA: Harvard University Press.Google Scholar
Bravo, A, Harms, KE and Emmons, LH (2010) Preference for collpa water by frugivorous bats (Artibeus): An experimental approach. Biotropica 42, 276280.CrossRefGoogle Scholar
Bravo, A, Harms, KE, Stevens, RD and Emmons, LH (2008) Collpas: Activity hotspots for frugivorous bats (Phyllostomidae) in the Peruvian Amazon. Biotropica 40, 203210. https://doi.org/10.1111/j.1744-7429.2007.00362.x CrossRefGoogle Scholar
Brightsmith, DJ (2008) The roles of soil characteristics and toxin adsorption in avian geophagy. Biotropica 40, 766774.CrossRefGoogle Scholar
Brown, JH and Davidson, DW (1977) Competition between seed-eating rodents and ants in desert ecosystems. Science 196, 880882.CrossRefGoogle ScholarPubMed
Brown, JH, Gillooly, JF, Allen, AP, Savage, VM, and West, GB (2004) Toward a metabolic theory of ecology. Ecology 85, 17711789.CrossRefGoogle Scholar
Castro, AAJF, Castro, ASrF, Farias, RRS, Sousa, SR, Castro, NvMCF, Silva, CuGB, Mendes, MRAj, Barros, JS and Lopes, RN (2009) Diversidade de espécies e de ecossistemas da vegetação remanescente da Serra Vermelha, área de chapada, municípios de Curimatá, Redenção do Gurguéia e Morro Cabeça no Tempo, sudeste do Piauí. Pubucações Avulsas em Conservação de Ecossistemas 23, 172.Google Scholar
Clay, NA, Donoso, DA and Kaspari, M (2015) Urine as an important source of sodium increases decomposition in an inland but not coastal tropical forest. Oecologia 177, 571579. https://doi.org/10.1007/s00442-014-3183-4 CrossRefGoogle Scholar
Clay, NA, Lehrter, RJ and Kaspari, M (2017) Towards a geography of omnivory: omnivores increase carnivory when sodium is limiting. Journal of Animal Ecology 86, 15231531.CrossRefGoogle ScholarPubMed
Clay, NA, Yanoviak, SP and Kaspari, M (2014) Short-term sodium inputs attract microbi-detritivores and their predators. Soil Biology and Biochemistry 75, 248253. https://doi.org/10.1016/j.soilbio.2014.04.021 CrossRefGoogle Scholar
Constantino, R (2005) Padrões de diversidade e endemismo de térmitas no bioma Cerrado. In: Scariot, A, Felfili, JM & Souza-Silva, JC (eds.). Ecologia e biodiversidade do Cerrado. Embrapa, Brasília. p. 319333.Google Scholar
Coutinho, LM (1978) O conceito de Cerrado. Revista Brasileira de Botânica 1, 1723.Google Scholar
da Silva, RR, Brandão, CRF and Silvestre, R (2004) Similarity between cerrado localities in Central and Southeastern Brazil based on the dry season bait visitors ant fauna. Studies on Neotropical Fauna and Environment 39, 191199.CrossRefGoogle Scholar
de Castro, EA and Kauffman, JB (1998) Ecosystem structure in the Brazilian Cerrado: a vegetation gradient of aboveground biomass, root mass and consumption by fire. Journal of Tropical Ecology 14, 263283.CrossRefGoogle Scholar
de Sousa, GG, Rodrigues, V dos S, Soares, S da C, Damasceno, IN, Fiusa, JN and Saraiva, EL (2018) Irrigation with saline water in soybean (Glycine max (L.) Merr.) in a soil with bovine biofertilizer. Revista Brasileira de Engenharia Agrícola e Ambiental 22, 604609.CrossRefGoogle Scholar
Dudley, R, Kaspari, M and Yanoviak, SP (2012) Lust for salt in the western Amazon. Biotroica 44, 69.CrossRefGoogle Scholar
Eiten, G (1972) The Cerrado vegetation of Brazil. Botânical Review 38, 201341.CrossRefGoogle Scholar
Ernesto, MV, Liberal, CN, Ferreira, AS, Alves, ACF, Zeppelini, D, Martins, CF, Pereira-Colavite, A, Creão-Duarte, A and Vasconcellos, A (2018) Hexapod decomposers of Serra de Santa Catarina, Paraíba, Brazil: an area with high potential for conservation of Caatinga biodiversity. Biota Neotropica 18, e20170410. http://dx.doi.org/10.1590/1676-0611-BN-2017-0410 CrossRefGoogle Scholar
Fearnside, PM (2000) Global warming and tropical land-use change: greenhouse gas emissions from biomass burning, decomposition, and soils in forest conversion, shifting cultivation and secondary vegetation. Climate Change 46, 115158.CrossRefGoogle Scholar
Frausto da Silva, JJR and Williams, RJP (2001) The biological chemistry of the elements: The inorganic chemistry of life, 2nd ed. Oxford, UK: Oxford University Press.Google Scholar
Garcia-Robledo, C, Chuquillanqui, H, Kuprewicz, EK and Escobar-Sarria, F (2018) Lower thermal tolerance in nocturnal than in diurnal ants: a challenge for nocturnal ectotherms facing global warming. Ecological Entomology 43, 162167.CrossRefGoogle Scholar
Gaston, KJ (2019) Nighttime ecology: The “nocturnal problem” revisited. The American Naturalist 193, https://doi.org/10.1086/702250 CrossRefGoogle ScholarPubMed
Geerling, JC and Loewy, AD (2008) Central regulation of sodium appetite. Experimental Physiology 93, 177209. https://doi.org/10.1113/expphysiol.2007.039891 CrossRefGoogle ScholarPubMed
Gillooly, JF, Brown, JH, West, GB, Savage, VM and Charnov, EL (2001) Effects of size and temperature on metabolic rate. Science 293, 22482251.CrossRefGoogle ScholarPubMed
Grant, CC and Scholes, MC (2006) The importance of nutrient hot-spots in the conservation and management of large wild mammalian herbivores in semi-arid savannas. Biological Conservation 130, 426437.CrossRefGoogle Scholar
Griffith, DM, Anderson, TM and Hamilton, EW III (2017) Ungulate grazing drives higher ramet turnover in sodium-adapted Serengeti grasses. Journal of Vegetation Science 28, 815823.CrossRefGoogle Scholar
Hare, KM, Pledger, S, Thompson, MB, Miller, JH and Daugherty, CH (2010) Nocturnal lizards from a cool-temperate environment have high metabolic rates at low temperatures. Journal of Comparative Physiology B 180, 11731181.CrossRefGoogle ScholarPubMed
Haridasan, M (1990) Solos do Distrito Federal. Pp. 309–330 in Pinto, M. N. (ed.). Cerrado: Caracterizaçao, Ocupaçao e Perspectivas. Editora da Universidade de Brasilia, Brasilia.Google Scholar
Hoffmann, WA, Geiger, EL, Gotsch, SG, Rossatto, DR, Silva, LCR, Lau, OL, Haridasan, M and Franco, AC (2012) Ecological thresholds at the savanna-forest boundary: how plant traits, resources and fire govern the distribution of tropical biomes. Ecology Letters 15, 759768.CrossRefGoogle ScholarPubMed
Hofmann, GS, Cardoso, MF, Alves, RJV, Weber, EJ, Barbosa, AA, de Toledo, PM, Pontual, FB, de O. Salles, L, Hasenack, H, Cordeiro, JLP, Aquino, FE and de Oliveira, LFB (2021) The Brazilian Cerrado is becoming hotter and drier. Global Change Biology, https://doi.org/10.1111/gcb.15712 CrossRefGoogle ScholarPubMed
Hölker, F, Wolter, C, Perkin, EK and Tockner, K (2010) Light pollution as a biodiversity threat. Trends in Ecology and Evolution 25, 681682.CrossRefGoogle ScholarPubMed
Hölldobler, B and Wilson, EO (1990) The ants. Harvard University Press, Cambridge, MA.CrossRefGoogle Scholar
Hooper, DU, Chapin, FS, Ewell, JJ, Hector, A, Inchausti, P, Lavorel, S et al. (2005) Effects of biodiversity on ecosystem functioning: a consensus of current knowledge. Ecological Monographs 75, 335.CrossRefGoogle Scholar
IBM Corp. (2019) IBM SPSS Statistics for Windows, Version 26.0. Armonk, NY: IBM Corp.Google Scholar
Jia, Y, Kong, X, Weiser, MD, Lv, Y, Akbar, S, Jia, X, Tian, K, He, Z, Lin, H, Bei, Z and Tian, X (2015) Sodium limits litter decomposition rates in a subtropical forest: Additional tests of the sodium ecosystem respiration hypothesis. Applied Soil Ecology 93, 98104. https://doi.org/10.1016/j.apsoil.2015.04.012 CrossRefGoogle Scholar
Jouquet, P, Traoré, S, Choosai, C, Hartmann, C and Bignell, D (2011) Influence of termites on ecosystem functioning. Ecosystem services provided by termites. European Journal of Soil Biology 47, 215222. doi: 10.1016/j.ejsobi.2011.05.005 CrossRefGoogle Scholar
Kaspari, M (2020) The seventh macronutrient: how sodium shortfall ramifies through populations, food webs and ecosystems. Ecology Letters 23, 11531168.CrossRefGoogle ScholarPubMed
Kaspari, M, Chang, C and Weaver, J (2010) Salted roads and sodium limitation in a northern forest ant community. Environmental Entomology 35, 543548.Google Scholar
Kaspari, M, Clay, NA, Donoso, DA and Yanoviak, SP (2014) Sodium fertilization increases termites and enhances decomposition in an Amazonian forest. Ecology 95, 795800. https://doi.org/10.1890/13-1274.1 CrossRefGoogle Scholar
Kaspari, M, Welti, EAR and de Beurs, KM (2020) The nutritional geography of ants: Gradients of sodium and sugar limitation across North American grasslands. Journal of Animal Ecology 89, 276284.CrossRefGoogle ScholarPubMed
Kaspari, M and Yanoviak, SP (2009) Biogeochemistry and the structure of tropical brown food webs. Ecology 90, 33423351.CrossRefGoogle ScholarPubMed
Kaspari, M, Yanoviak, SP and Dudley, R (2008) On the biogeography of salt limitation: A study of ant communities. Proceedings of the National Academy of Sciences, USA 105, 1784817851. doi. 10.1073pnas.0804528105 CrossRefGoogle ScholarPubMed
Kaspari, M, Yanoviak, SP, Dudley, R, Yuan, M and Clay, NA (2009) Sodium shortage as a constraint on the carbon cycle in an inland tropical rainforest. Proceedings of the National Academy of Sciences of the United States of America 106, 1940519409. https://doi.org/10.1073/pnas.0906448106 CrossRefGoogle Scholar
Kellman, M, Miyanishi, K and Hiebert, P (1985) Nutrient retention by savanna ecosystems: II. Retention after fire. Journal of Ecology 73, 953962.CrossRefGoogle Scholar
Kingsolver, JG and Huey, RB (2008) Size, temperature, and fitness: three rules. Evolutionary Ecology Research 10, 251268.Google Scholar
Klink, CA and Machado, RB (2005) A conservação do Cerrado Brasileiro. Megadiversidade 1, 147155.Google Scholar
Klunk, CL, Giehl, ELH, Lopes, BC, Marcineiro, FR and Rosumek, FB (2018) Simple does not mean poor: grasslands and forest harbor similar ant species richness and distinct composition in highlands of southern Brazil. Biota Neotropica 18, e20170507. http://dx.doi.org/10.1590/1676-0611-BN-2017-0507 CrossRefGoogle Scholar
Lopes, AS and Guilherme, LRG (2016) Chapter One – A career perspective on soil management in the Cerrado region of Brazil. Advances in Agronomy 137, 172.CrossRefGoogle Scholar
Lopes, CT and Vasconcelos, HL (2008) Evaluation of three methods for sampling ground-dwelling ants in the Brazilian Cerrado. Neotropical Entomology 37, 399405.CrossRefGoogle ScholarPubMed
Machado, RB, Aguiar, LFS, Neto, MBR, Rodrigues, FHG, Hass, A and Aquino, FG (2004) Atlas da Conservação da Natureza Brasileira: Unidades Federais. São Paulo, SP: Metalivros.Google Scholar
Mafa, SM, Malgas, S, Bhattacharya, A, Rashamuse, K and Pletscke, BI (2020) The effects of alkaline pretreatment on agricultural biomasses (corn cob and sweet sorghum bagasse) and their hydrolysis by a termite-derived enzyme cocktail. Agronomy 10, 1211; doi: 10.3390/agronomy10081211 CrossRefGoogle Scholar
Marques, GDV and Del Claro, K (2006) The ant fauna in a Cerrado area: The influence of vegetation structure and seasonality (Hymenoptera: Formicidae). Sociobiology 47, 235252.Google Scholar
McNaughton, SJ, Banyikwa, FF and McNaughton, MM (1997) Promotion of the cycling of diet-enhancing nutrients by African grazers. Science 278, 17981800.CrossRefGoogle ScholarPubMed
Medeiros, RA and Haridasan, M (1985) Seasonal variations in the foliar concentrations of nutrients in some aluminium accumulating and non-accumulating species of the cerrado region of central Brazil. Plant Soil 88, 433436 CrossRefGoogle Scholar
Medina, E, Mendoza, A and Montes, R (1978) Nutrient balance and organic matter production in the Trachypogon savannas of Venezuela. Tropical Agriculture (Trinidad) 55, 243253.Google Scholar
Mikaelyan, A, Dietrich, C, Köhler, T, Poulsen, M, Sillam-Dussès, D and Brune, A (2015) Diet is the primary determinant of bacterial community structure in the guts of higher termites. Molecular Ecology 24, 52845295.CrossRefGoogle ScholarPubMed
Montes, R and Medina, E (1977) Seasonal changes in nutrient content of leaves of savanna trees with different ecological behavior. Geo-Eco-Trop 4, 295307.Google Scholar
Myers, N, Mittermeier, RA, Mittermeier, CG, Da Fonseca, GAB and Kent, J (2000) Biodiversity hotspots for conservation priorities. Nature 403, 853858. doi: 10.1038/35002501 CrossRefGoogle ScholarPubMed
Nimer, E (1989) Climatologia da região nordeste. In Climatologia do Brasil, 315361. Estatística, FIBdGe (Eds). Rio de Janeiro, Brazil: Fundação Instituto Brasileiro de Geografia e Estatística – IBGE.Google Scholar
Pellegrini, AFA (2016) Nutrient limitation in tropical savannas across multiple scales and mechanisms. Ecology 97, 313324.CrossRefGoogle ScholarPubMed
Peters, MK, Mayr, A, Röder, J, Sanders, NJ and Steffan-Dewenter, I (2014) Variation in nutrient use in ant assemblages along an extensive elevational gradient on Mt Kilimanjaro. Journal of Biogeography 41, 22452255.CrossRefGoogle Scholar
Peters, RH (1986) The ecological implications of body size. Cambridge University Press, Cambridge, UK.Google Scholar
Powers, JS and Marín-Spiotta, E (2017) Ecosystem processes and biogeochemical cycles in secondary tropical forest succession. Annual Review of Ecology, Evolution, and Systematics 48, 497519.CrossRefGoogle Scholar
Prather, RM, Roeder, KA, Sanders, NJ and Kaspari, M (2018) Using metabolic and thermal ecology to predict temperature dependent ecosystem activity: a test with prairie ants. Ecology 99, 21132121.CrossRefGoogle ScholarPubMed
Raubenheimer, D, Simpson, SJ and Mayntz, D (2009) Nutrition, ecology and nutritional ecology: toward an integrated framework. Functional Ecology 23, 416. https://doi.org/10.1111/j.1365-2435.2008.01522.x CrossRefGoogle Scholar
Resasco, J, Porter, SD, Sanders, NJ and Levey, DJ (2014) Assessing the effects of sodium on fire ant foraging in the field and colony growth in the laboratory. Ecological Entomology 39, 267271.CrossRefGoogle Scholar
Risch, AC, Zimmermann, S, Ohashi, M, Finer, L, Kho, LK and Schultz, M (2016) First evidence that the sodium ecosystem respiration hypothesis may also hold for a coastal tropical rainforest. Applied Soil Ecology 108, 9295. http://dx.doi.org/10.1016/j.apsoil.2016.08.007 CrossRefGoogle Scholar
Rothman, JM, Van Soest, PJ and Pell, AN (2006) Decaying wood is a sodium source for mountain gorillas. Biology Letters 2, 321324.CrossRefGoogle Scholar
Sano, EE, Rosa, R, Brito, JLS and Ferreira, LG (2010) Land cover mapping of the tropical savanna region in Brazil. Environmental Monitoring and Assessment 166, 113124. doi: 10.1007/s10661-009-0988-4 CrossRefGoogle ScholarPubMed
Schulkin, J (1991) Sodium Hunger: The Search for a Salty Taste. Cambridge University Press.Google Scholar
Seastedt, TR and Crossley, DA Jr. (1981) Sodium dynamics in forest ecosystems and the animal starvation hypothesis. The American Naturalist 117, 10291034.CrossRefGoogle Scholar
Silva, JMC and Bates, JM (2002) Biogeographic patterns and conservation in the South American Cerrado: a tropical savanna hotspot. BioScience 52, 225234. doi: 10.1641/0006-3568(2002)052[0225:BPACIT]2.0.CO;2 CrossRefGoogle Scholar
Silvestre, R and Brandão, CRF (2000) Formigas (Hymenoptera, Formicidae) atraídas a iscas em uma “ilha” de Cerrado no município de Cajuru, estado de São Paulo, Brasil. Revista Brasileira de Entomologia 44, 7177.Google Scholar
Spotti, FA, Castracani, C, Grasso, DA and Mori, A (2014) Daily activity patterns and food preferences in an alpine ant community. Ethology Ecology & Evolution. doi: 10.1080/03949370.2014.947634 Google Scholar
Sterner, RW and Elser, JJ (2002) Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere. Princeton University Press.Google Scholar
Tolsma, OJ, Ernst, WHO, Vermeij, RA and Vooijs, R (1987) Seasonal variation of nutrient concentrations in a semi-arid savanna ecosystem in Botswana. Journal of Ecology 75, 755770.CrossRefGoogle Scholar
Townsend, AR, Cleveland, CC, Houlton, BZ, Alden, CB and White, JWC (2011) Multi-element regulation of the tropical forest carbon cycle. Frontiers in Ecology and the Environment 9, 917.CrossRefGoogle Scholar
Tuma, J, Eggleton, P and Fayle, TM (2020) Ant-termite interactions: an important but under-explored ecological linkage. Biological Reviews 95, 555572.CrossRefGoogle ScholarPubMed
Viana-Junior, AB, Souza, VB, Reis, YT and Marques-Costa, AP (2014) Termite assemblages in dry tropical forest of Northeastern Brazil: are termites bioindicators of environmental disturbance? Sociobiology 61, 324331.CrossRefGoogle Scholar
Vieira, J and Vasconcelos, HL (2015) Inter-generic and inter-habitat variation in the demand for sodium by Neotropical ants. Insectes Sociaux 62, 133140.CrossRefGoogle Scholar
Vonshak, M, Dayan, T and Kronfeld-Schor, N (2009) Arthropods as a prey resource: Patterns of diel, seasonal, and spatial availability. Journal of Arid Environments 73, 458462.CrossRefGoogle Scholar
Welti, EAR, Kuczynski, L, Marske, DA, Sanders, NJ, de Beurs, KM and Kaspari, M (2020) Salty, mild, and low plant biomass grasslands increase top-heaviness of invertebrate trophic pyramids. Global Ecology and Biogeography 29, 14741485.CrossRefGoogle Scholar
Welti, EAR, Sanders, NJ, de Beurs, KM and Kaspari, M (2019) A distributed experiment demonstrates widespread sodium limitation in grassland food webs. Ecology 100, e02600. https://doi.org/10.1002/ecy.2600 CrossRefGoogle ScholarPubMed
Yoshimura, T, Kagemori, N, Kawai, S, Sera, K and Futatsugawa, S (2002) Trace elements in termites by PIXE analysis. Nuclear Instruments and Methods in Physics Research B 189, 450453.CrossRefGoogle Scholar
Zeh, DW (1990) The Biology of Scorpions; Polis, G. A., Ed.; Stanford University Press: Stanford, CA, USA.Google Scholar