"Latitudinal Gradients in Species Diversity": Reflections on Pianka's 1966 Article and a Look Forward.

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Previous articleNext article FreeHistorical Comment“Latitudinal Gradients in Species Diversity”: Reflections on Pianka’s 1966 Article and a Look ForwardDouglas W. Schemske and Gary G. MittelbachDouglas W. Schemske1. W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, Michigan 490602. Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824*Corresponding author; e-mail: [email protected]. Search for more articles by this author and Gary G. Mittelbach1. W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, Michigan 490603. Department of Integrative Biology, Michigan State University, East Lansing, Michigan 48824 Search for more articles by this author PDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreI was a mere graduate student, wet behind the ears, only 25 years old, when I wrote it. I don’t usually re-read my own papers—but now, five decades later, I am pleased to find it cerebral and fairly well written.Eric Pianka, 2016Just as the 1960s were marked by revolutionary changes in music, culture, and politics, so too were they foundational for the emergence of modern ecology, with classical observational approaches giving way to mathematical theory and experiments. The University of Washington was a crucible for this movement in the 1960s, with young faculty such as Bob Paine, Gordon Orians, and Alan Kohn working in close collaboration with a number of exceptionally creative graduate students, including Henry Horn, Eric Pianka, Christopher Smith, Jared Verner, and Mary Willson. Collectively, this group pioneered a new way of thinking about ecological problems and was instrumental in defining the discipline of evolutionary ecology, a union of ecological and evolutionary perspectives that mirrors the goals of the American Society of Naturalists: “to advance and to diffuse knowledge of organic evolution and other broad biological principles.”Of the many notable contributions by the Washington group, Eric Pianka’s 1966 article “Latitudinal Gradients in Species Diversity: A Review of Concepts” is emblematic of the creative energy at work during this era to address big problems in ecology and evolution. The paper was the first chapter of Eric’s PhD dissertation (1965), “Species Diversity and Ecology of Flatland Desert Western North America,” which (like many graduate students at the time) he painstakingly typed himself (fig. 1).Figure 1. Eric Pianka typing his dissertation. Photo courtesy of E. Pianka.View Large ImageDownload PowerPointEric’s influential paper (as of February 2017: 1,536 citations, Google Scholar; 967 citations, Web of Science) provided the first synthesis of the major hypotheses for the latitudinal diversity gradient (LDG) and stimulated the research trajectories of legions of naturalists. It has been reprinted in three different volumes of classic papers, including tropical ecology (Jordan 1981), tropical forest biology (Chazdon and Whitmore 2002), and biogeography (Lomolino et al. 2004), and thus it continues to serve as a foundational reference for the study of geographic patterns of biodiversity.In reviewing previous studies, Pianka compiled six hypotheses that addressed possible causes of the LDG (Table 1). For each, he provided a rationale for the biological processes involved. He did not evaluate the validity of the hypotheses or identify those he considered most plausible, but where possible, he did identify areas of future research. One important theme he highlighted throughout the paper is the challenge of distinguishing different mechanisms that might generate the same pattern: “Obviously, there is room for considerable overlap between these different hypotheses, and several may be acting in concert or in series in any particular situation” (Pianka 1966, p. 42). Below we briefly summarize Pianka’s six hypotheses.Table 1. Pianka’s (1966) six hypotheses and Fine’s (2015) five hypotheses for the latitudinal diversity gradientHypothesisOur interpretation of the main focusPianka 1966: 1. The time theoryEcology and evolution 2. The theory of spatial heterogeneityEcology 3. The competition hypothesisEcology 4. The predation hypothesisEcology 5. The theory of climatic stabilityEcology and evolution 6. The productivity hypothesisEcologyFine 2015: 1. Time-integrated area, energy, and tropical niche conservatismEvolution 2. Climate stabilityEvolution 3. Temperature and evolutionary speedEvolution 4. Biotic interactions and speciation rateEvolution 5. Biotic interactions and finer nichesEcologyView Table ImageHypothesis 1. The time theory proposes that the species richness of communities increases with time due to ecological (immigration) and evolutionary (speciation) processes. Multiple glaciations in northern latitudes reduced the time available for diversification, while tropical regions remained relatively undisturbed, leading to the LDG.Hypothesis 2. The theory of spatial heterogeneity suggests that the LDG results from the greater heterogeneity and/or complexity of physical and biotic factors (e.g., foliage height diversity) in the tropics. This is essentially an argument that the number of available habitats controls the number of species in a community.Hypothesis 3. The competition hypothesis proposes that natural selection in the temperate zone is governed more by abiotic than by biotic factors, and as a result, competition is stronger in the tropics, niches are narrower, and more species can be supported.Hypothesis 4. The predation hypothesis is an alternative to the competition hypothesis, suggesting that competition is actually lower in the tropics due to a reduction in population sizes caused by higher predation in tropical environments. Lower competition reduces the likelihood of competitive exclusion and increases species richness.Hypothesis 5. The theory of climatic stability predicts that the stable climate in tropical regions leads to greater specialization, narrower niches, and higher species richness.Hypothesis 6. The productivity hypothesis suggests that the greater productivity of tropical regions increases species richness, perhaps by allowing narrower niches, tighter species packing, and greater niche overlap.Pianka’s Hypotheses RevisitedPianka’s 1966 article synthesized the wide range of ideas regarding the causes of the LDG in hopes of stimulating new research. Fifty years after its publication, there is still no consensus as to the primary mechanisms that contribute to the origin and maintenance of the LDG. Yet the remarkable diversity of life found in the humid tropics is as fascinating to biologists today as it was to Pianka in 1966 or to Wallace and Darwin more than 150 years ago. Here we briefly review how each of the six hypotheses summarized by Pianka has fared over the past 50 years.The time hypothesis, which dates back to A. R. Wallace, is perhaps the oldest and most widely accepted of the six hypotheses. Since Pianka, development of detailed databases on the fossil record and knowledge of paleoclimates has provided a clearer of picture of the development of biodiversity through deep time, and this has provided new opportunities for examining the time hypothesis (Jablonski et al. 2017). For example, a time-integrated biogeographic analysis of diversification in forest trees has suggested that tropical environments are older and thus have had more time for diversification (reviewed in Fine 2015), consistent with the time hypothesis. However, empirical tests of this hypothesis are challenging because it is difficult to separate the effects of age and climate (tropical vs. temperate). If tropical environments are older, historically larger, and more diverse, is the increased diversity due to age, area, climate, or all of the above? A recent approach to this problem examined the joint effects of time, area, and latitude on speciation of endemic fish and found that age, area, and latitude have significant and equivalent effects (Hanly et al. 2017). As one striking example that time per se is not the only factor contributing to fish diversification, consider that Lake Baikal, located at 55.63°N, is the largest by volume and the oldest (>27 million years) lake in the world, yet it has just 52 species of fish, 37 of which are endemic. In comparison, Lake Victoria, located at 1.30°S, is just 18,000 years old, yet it has 566 species, of which 450 are endemic.The theory of spatial heterogeneity has received little attention since Pianka’s review, which probably reflects the general opinion that tropical regions do not display greater heterogeneity of the physical environment. However, there is evidence that tropical forests have greater heterogeneity in tree height, which may contribute to the increased diversity of short-statured species in tropical forests (King et al. 2006). The role of biotic interactions in the LDG has expanded beyond the competition and predation hypotheses that were the focus of Pianka’s review to include mutualisms such as pollination, which may promote reproductive isolation of plants and their pollinators. This has led to renewed interest in Dobzhansky’s proposal that the greater importance of biotic interactions in the tropics promotes diversification (Dobzhansky 1950). A recent review of latitudinal patterns in the strength of biotic interactions largely confirms Dobzhansky’s hypothesis, although more data are needed (Schemske et al. 2009). Although Dobzhansky did not provide a mechanism linking biotic interactions to the LDG, a recent extension of his ideas suggests that strong biotic interactions coupled with coevolution lead to faster rates of adaptation and speciation in the tropics (Schemske 2009).The theory of climatic stability remains relatively unexplored, although interest has been renewed in Janzen’s idea that mountains are a greater barrier to gene flow in the tropics than in temperate zones and that this may contribute to diversification. This hypothesis that “mountain passes are higher in tropics” is based on the idea that populations physiologically adapted to cold, high-elevation habitats in the aseasonal tropics are less likely to migrate across warmer valleys than are their temperate counterparts that are adapted to far greater seasonal variation in temperature (Janzen 1967). Finally, although the productivity hypothesis has been reviewed extensively, both with respect to geographic patterns in community diversity and to the LDG specifically, a direct mechanism linking productivity to species richness remains elusive.Current Hypotheses for the LDG: An Emphasis on EvolutionPianka’s six hypotheses for the latitudinal diversity gradient (Table 1) focus predominantly on mechanisms of species coexistence: “The question of basic ecological interest is … what are the factors that allow ecological coexistence of more species at low latitudes?” (Pianka 1966, p. 34). Interestingly, in the more than 50 years since Pianka’s review, explanations for the LDG now place greater emphasis on evolutionary mechanisms (Mittelbach et al. 2007). For example, Fine (2015) reviews five hypotheses for the LDG (Table 1), including latitudinal differences in rates of diversification (speciation and/or extinction) and their drivers and differences in the time and area available for diversification in tropical and temperate biomes (in combination with tropical niche conservatism and available energy). Only one of Fine’s hypotheses is purely ecological.Understandably, Pianka’s 1966 review focused mainly on ecology. Interspecific competition and species coexistence via niche partitioning formed the foundation of community ecology in the 1960s. These processes were thought to determine the number of species found in most local communities and, by extension, patterns of species diversity at broader spatial scales. Pianka also may have given evolution less emphasis because evolutionary hypotheses were thought untestable at the time. For example, he suggested (Pianka 1966, p. 35) that “the evolutionary time theory is not readily amenable to conclusive tests, and will probably remain more or less unevaluated for some time.” Since Pianka’s review, technological advances on a variety of fronts have made it possible to test evolutionary hypotheses. For example, molecular phylogenies allow the estimation of clade-specific diversification rates in relation to climate, latitude, and other factors. Further, satellite imagery and GIS mapping now provide unprecedented means to characterize global patterns of landform, climate, productivity, and species richness. These and other technological achievements have greatly advanced both paleo- and neontological studies of the LDG (Jablonski et al. 2017.The Question of Coexistence Still MattersThe current emphasis on historical and evolutionary hypotheses for the LDG is a welcome and needed addition to the ecological hypotheses that figured so prominently in Pianka’s early review. However, we should not lose sight of the question of species coexistence. Even if evolution produces more species in the tropics compared to the temperate zone (e.g., due to higher speciation rates and/or a longer evolutionary history), unless interspecific competition is always weak and communities are unsaturated, we still need to explain how more species can coexist at low latitudes than high.One explanation for why more species are able to coexist in the tropics than in the temperate zone is that primary productivity is higher in the tropics, allowing more individuals to be supported per unit area and, therefore, more species (hypothesis 6 in Pianka’s list; Table 1). However, for well-documented taxa such as birds and trees, the increase in numbers of individuals per unit area from high latitudes to low latitudes is small compared to the dramatic increase in species richness (Currie et al. 2004; Brown 2014), suggesting that the productivity hypothesis by itself is insufficient. Another long-held hypothesis for enhanced species coexistence in the tropics (included at multiple points by Pianka) is that tropical species have narrower niches, which allows tighter species packing in tropical communities. Indeed, many examples of tropical species with very specialized niches exist, yet results from individual studies and from meta-analyses are mixed. Major obstacles to testing the narrower-niches hypothesis include the poor quality of the data (few studies have collected data specifically to test the hypothesis), the limited geographic scope of studies, and the wide variation in sampling methods. Much more work is needed to better test the narrower-niches hypotheses. Below, we suggest two additional mechanisms (not discussed in Pianka’s review) that may promote greater niche diversity and allow more species to coexist in the tropics relative to the temperate zone.Species as NichesBiotic interactions coupled with speciation may greatly expand the available niche space. As suggested by Vermeij (2005), “Every species is potentially a resource on which some other species can in principle specialize or to which another species must adapt.” More simply, species can be niches for other species. Consider the army ant Eciton burchellii, which forages in large swarms and collects thousands of arthropod prey for the colony in a single day. More than 300 species of insects, birds, and other organisms depend on E. burchellii for all or part of their livelihood (e.g., eating prey the ants collect or flush, consuming the waste they discard, living in ant nests, riding on ant bodies, and more). Rettenmeyer et al. (2011) speculate that the more than 300 known associate species of E. burchellii are “likely only the tip of the iceberg,” with thousands of specimens yet to be described and their associations characterized. Army ants are a spectacular example of how even a single species may create niches for other species. There are many such examples in nature, and they seem far more common at low latitudes than high, but no studies have attempted to quantify this difference.Novel NichesPrice (2008) suggested that “at least 50% of the increase in (bird) species numbers in the tropics is due to the presence of unusual niches.” This is likely a “best guess,” but there is little doubt that tropical species occupy a variety of novel niches rarely found in the temperate zone. Further, many of these niches are functionally associated with warm temperatures and stable environments and thus may not be possible in a seasonally cold climate. For example, many tropical fish species are herbivorous or frugivorous, but these feeding modes are rare at high latitudes. Other, more unusual, feeding modes such as scale and fin eating have evolved many times in tropical fishes but are essentially absent in temperate fishes. A strong case can be made that herbivory is metabolically feasible only in warm environments for fishes and probably most poikilotherms. However, why other novel niches (e.g., scale eating, parasite cleaning, electrical communication, and predation in fishes; flower piercing, ant following, and herbivory in birds; ant eating, blood feeding in mammals) are common in the tropics but are much rarer in the extratropics deserves further study.The Next 50 Years?Pianka’s article was a milestone in organizing the myriad hypotheses for the LDG into a manageable framework for future study. What will the next 50 years bring? First, we are hopeful that current and future naturalists will continue to investigate the ecological and evolutionary mechanisms that contribute to the LDG. Second, and perhaps most important, is to ask how much tropical diversity will remain 50 years from now and to explore what can be done to preserve it. At the very time when we are developing the scientific tools to deeply probe and understand the causes of the LDG, that diversity is rapidly disappearing. What will be left for future naturalists to study? This question was largely absent 50 years ago but now demands our attention.AcknowledgmentsWe thank J. Bronstein for encouragement to write the article, E. Pianka and J. Bronstein for thoughtful comments, and the National Science Foundation for support through grant DEB-1456615. This is contribution 1982 from the Kellogg Biological Station.Literature CitedBrown, J. H. 2014. Why are there so many species in the tropics? Journal of Biogeography 41:8–22.First citation in articleCrossref MedlineGoogle ScholarChazdon, R., and T. Whitmore, eds. 2002. Foundations of tropical forest biology: classic papers with commentaries. University of Chicago Press, Chicago.First citation in articleGoogle ScholarCurrie, D. J., G. G. Mittelbach, H. V. Cornell, R. Field, J.-F. Guégan, B. A. Hawkins, D. M. Kaufman, et al. 2004. Predictions and tests of climate-based hypotheses of broad-scale variation in taxonomic richness. Ecology Letters 7:1121–1134.First citation in articleCrossrefGoogle ScholarDobzhansky, T. 1950. Evolution in the tropics. American Scientist 38:209–221.First citation in articleGoogle ScholarFine, P. V. A. 2015. Ecological and evolutionary drivers of geographic variation in species diversity. Annual Review of Ecology, Evolution, and Systematics 46:369–392.First citation in articleCrossrefGoogle ScholarHanly, P. J., G. G. Mittelbach, and D. W. Schemske. 2017. Speciation and the latitudinal diversity gradient: insights from the global distribution of endemic fish. American Naturalist 189:604–615.First citation in articleLinkGoogle ScholarJablonski, D., S. Huang, K. Roy, and J. W. Valentine. 2017. Shaping the latitudinal diversity gradient: new perspectives from a synthesis of paleobiology and biogeography. American Naturalist 189:1–12.First citation in articleLinkGoogle ScholarJanzen, D. H. 1967. Why mountain passes are higher in the tropics. American Naturalist 101:233–249.First citation in articleLinkGoogle ScholarJordan, C. F., ed. 1981. Tropical ecology: benchmark papers in ecology. Hutchinson Ross, Stroudsburg, PA.First citation in articleGoogle ScholarKing, D. A., S. J. Wright, and J. H. Connell. 2006. The contribution of interspecific variation in maximum tree height to tropical and temperate diversity. Journal of Tropical Ecology 22:11–24.First citation in articleCrossrefGoogle ScholarLomolino, M. V., D. F. Sax, and J. H. Brown. 2004. Foundations of biogeography: classic papers with commentaries. University of Chicago Press, Chicago.First citation in articleGoogle ScholarMittelbach, G. G., D. W. Schemske, H. V. Cornell, A. P. Allen, J. M. Brown, M. B. Bush, S. P. Harrison, et al. 2007. Evolution and the latitudinal diversity gradient: speciation, extinction and biogeography. Ecology Letters 10:315–331.First citation in articleCrossref MedlineGoogle ScholarPianka, Eric R. 1966. Latitudinal gradients in species diversity: a review of concepts. American Naturalist 100:33–46.First citation in articleLinkGoogle ScholarPrice, T. D. 2008. Speciation in birds. Roberts, Greenwood Village, CO.First citation in articleGoogle ScholarRettenmeyer, C. W., M. E. Rettenmeyer, J. Joseph, and S. M. Berghoff. 2011. The largest animal association centered on one species: the army ant Eciton burchellii and its more than 300 associates. Insectes Sociaux 58:281–292.First citation in articleCrossrefGoogle ScholarSchemske, D. W. 2009. Biotic interactions and speciation in the tropics. Pages 219–239 in R. K. Butlin, J. R. Bridle, and D. Schluter, eds. Speciation and patterns of diversity. Cambridge University Press, Cambridge.First citation in articleGoogle ScholarSchemske, D. W., H. V. Cornell, G. G. Mittelbach, K. Roy, and J. M. Sobel. 2009. Is there a latitudinal gradient in the importance of biotic interactions? Annual Review of Ecology, Evolution, and Systematics 40:245–269.First citation in articleCrossrefGoogle ScholarVermeij, G. J. 2005. From phenomenology to first principles: towards a theory of diversity. Proceedings of the California Academy of Sciences 56(suppl. I, no. 2):12–23.First citation in articleGoogle Scholar “One of the largest and most formidable looking, though perfectly harmless, insects we have, is the Corydalus cornutus. . . . Insects like this were characteristic of the Coal Period, probably breeding in the marshes and fens of Carboniferous times.” From “Natural history miscellany: zoölogy” (The American Naturalist, 1867, 1:434–439).View Large ImageDownload PowerPoint Previous articleNext article DetailsFiguresReferencesCited by The American Naturalist Volume 189, Number 6June 2017 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/691719 HistoryPublished online April 18, 2017 © 2017 by The University of Chicago. All rights reserved.PDF download Crossref reports the following articles citing this article:Simone Fattorini Biogeographical Patterns of Earwigs in Italy, Insects 14, no.33 (Feb 2023): 235.https://doi.org/10.3390/insects14030235Simone Fattorini Global Patterns of Earwig Species Richness, Diversity 14, no.1010 (Oct 2022): 890.https://doi.org/10.3390/d14100890Chloé Schmidt, Gabriel Muñoz, Lesley T. Lancaster, Jean‐Philippe Lessard, Katharine A. Marske, Katie E. Marshall, Colin J. Garroway Population demography maintains biogeographic boundaries, Ecology Letters 25, no.88 (Jun 2022): 1905–1913.https://doi.org/10.1111/ele.14058Simone Fattorini Odonate Diversity Patterns in Italy Disclose Intricate Colonization Pathways, Biology 11, no.66 (Jun 2022): 886.https://doi.org/10.3390/biology11060886Yu Zhang, Yi-Gang Song, Can-Yu Zhang, Tian-Rui Wang, Tian-Hao Su, Pei-Han Huang, Hong-Hu Meng, Jie Li Latitudinal Diversity Gradient in the Changing World: Retrospectives and Perspectives, Diversity 14, no.55 (Apr 2022): 334.https://doi.org/10.3390/d14050334Ann M. Raiho, Henry R. Scharf, Carl A. Roland, David K. Swanson, Sarah E. Stehn, Mevin B. Hooten, Sabine Rumpf Searching for refuge: A framework for identifying site factors conferring resistance to climate‐driven vegetation change, Diversity and Distributions 28, no.44 (Mar 2022): 793–809.https://doi.org/10.1111/ddi.13492Héctor Tejero‐Cicuéndez, Pedro Tarroso, Salvador Carranza, Daniel L. Rabosky, Daniel Pincheira‐Donoso Desert lizard diversity worldwide: Effects of environment, time, and evolutionary rate, Global Ecology and Biogeography 31, no.44 (Feb 2022): 776–790.https://doi.org/10.1111/geb.13470Tomas Roslin, Panu Somervuo, Mikko Pentinsaari, Paul D. N. Hebert, Jireh Agda, Petri Ahlroth, Perttu Anttonen, Jouni Aspi, Gergin Blagoev, Santiago Blanco, Dean Chan, Tom Clayhills, Jeremy deWaard, Stephanie deWaard, Tyler Elliot, Riikka Elo, Sami Haapala, Eero Helve, Jari Ilmonen, Petri Hirvonen, Chris Ho, Juhani Itämies, Vladislav Ivanov, Jevgeni Jakovlev, Aino Juslén, Reijo Jussila, Jere Kahanpää, Lauri Kaila, Jari‐PekkaKaitila, Ari Kakko, Iiro Kakko, Ali Karhu, Sami Karjalainen, Jostein Kjaerandsen, Janne Koskinen, Erkki M. Laasonen, Leena Laasonen, Erkka Laine, Petri Lampila, Valerie Levesque‐Beaudin, Liuqiong Lu, Meri Lähteenaro, Pekka Majuri, Sampsa Malmberg, Ramya Manjunath, Petri Martikainen, Jaakko Mattila, Jaclyn McKeown, Petri Metsälä, Margarita Miklasevskaja, Meredith Miller, Renee Miskie, Arto Muinonen, Veli‐MattiMukkala, Suresh Naik, Nadia Nikolova, Kari Nupponen, Otso Ovaskainen, Ika Österblad, Lauri Paasivirta, Timo Pajunen, Petri Parkko, Juho Paukkunen, Ritva Penttinen, Kate Perez, Jaakko Pohjoismäki, Sean Prosser, Martti Raekunnas, Miduna Rahulan, Meeri Rannisto, Sujeevan Ratnasingham, Pekka Raukko, Aki Rinne, Teemu Rintala, Susana Miranda Romo, Jukka Salmela, Juha Salokannel, Riitta Savolainen, Leif Schulman, Pasi Sihvonen, Dina Soliman, Jayme Sones, Claudia Steinke, Gunilla Ståhls, Jukka Tabell, Mikko Tiusanen, Gergely Várkonyi, Eero J. Vesterinen, Esko Viitanen, Veli Vikberg, Matti Viitasaari, Jussi Vilen, Connor Warne, Catherine Wei, Kaj Winqvist, Evgeny Zakharov, Marko Mutanen A molecular‐based identification resource for the arthropods of Finland, Molecular Ecology Resources 22, no.22 (Nov 2021): 803–822.https://doi.org/10.1111/1755-0998.13510A.O. Achieng, B. Opaa, K.O. Obiero, O. Osano, B. Kaunda-Arara Watershed Management in Kenya; Societal Implications, Drivers of Change and Governance Needs, (Jan 2022): 464–474.https://doi.org/10.1016/B978-0-12-819166-8.00157-2Rajendra Mohan Panda Introduction, (Sep 2022): 1–32.https://doi.org/10.1007/978-3-031-13347-3_1Alexander T. Neu, Eric E. Allen, Kaustuv Roy Do host‐associated microbes show a contrarian latitudinal diversity gradient? Insights from Mytilus californianus , an intertidal foundation host, Journal of Biogeography 48, no.1111 (Aug 2021): 2839–2852.https://doi.org/10.1111/jbi.14243Leonora S. Bittleston, Zachary B. Freedman, Jessica R. Bernardin, Jacob J. Grothjan, Erica B. Young, Sydne Record, Benjamin Baiser, Sarah M. Gray, Ashley Shade, Ashish Malik Exploring Microbiome Functional Dynamics through Space and Time with Trait-Based Theory, mSystems 6, no.44 (Aug 2021).https://doi.org/10.1128/mSystems.00530-21Oskar Hagen, Benjamin Flück, Fabian Fopp, Juliano S. Cabral, Florian Hartig, Mikael Pontarp, Thiago F. Rangel, Loïc Pellissier, Andrew J. Tanentzap gen3sis: A general engine for eco-evolutionary simulations of the processes that shape Earth’s biodiversity, PLOS Biology 19, no.77 (Jul 2021): e3001340.https://doi.org/10.1371/journal.pbio.3001340Rachel M. Penczykowski and R. Drew Sieg Plantago spp. as Models for Studying the Ecology and Evolution of Species Interactions across Environmental Gradients, The American Naturalist 198, no.11 (Jun 2021): 158–176.https://doi.org/10.1086/714589Lucas Neves Perillo, Flávio Siqueira de Castro, Ricardo Solar, Frederico de Siqueira Neves Disentangling the effects of latitudinal and elevational gradients on bee, wasp, and ant diversity in an ancient neotropical mountain range, Journal of Biogeography 48, no.77 (Mar 2021): 1564–1578.https://doi.org/10.1111/jbi.14095Fernando A O Silveira, Peggy L Fiedler, Stephen D Hopper OCBIL theory: a new science for old ecosystems, Biological Journal of the Linnean Society 133, no.22 (Apr 2021): 251–265.https://doi.org/10.1093/biolinnean/blab038Ana Berenice García‐Andrade, Juan David Carvajal‐Quintero, Pablo A. Tedesco, Fabricio Villalobos, Fabien Leprieur Evolutionary and environmental drivers of species richness in poeciliid fishes across the Americas, Global Ecology and Biogeography 30, no.66 (Apr 2021): 1245–1257.https://doi.org/10.1111/geb.13299Navendu V. Page, Kartik Shanker, Diogo Borges Provete Climatic stability drives latitudinal trends in range size and richness of woody plants in the Western Ghats, India, PLOS ONE 15, no.77 (Jul 2020): e0235733.https://doi.org/10.1371/journal.pone.0235733Elizabeth R. Lawrence, Dylan J. Fraser, Brian McGill Latitudinal biodiversity gradients at three levels: Linking species richness, population richness and genetic diversity, Global Ecology and Biogeography 29, no.55 (Feb 2020): 770–788.https://doi.org/10.1111/geb.13075Juan Pablo Gomez, José Miguel Ponciano, Gustavo A. Londoño, Scott K. Robinson, Erica Fleishman The biotic interactions hypothesis partially explains bird species turnover along a lowland Neotropical precipitation gradient, Global Ecology and Biogeography 29, no.33 (Dec 2019): 491–502.https://doi.org/10.1111/geb.13047Jonas B. Maravalhas, Heraldo L. Vasconcelos, Jean‐Philippe Lessard Ant diversity in Neotropical savannas: Hierarchical processes acting at multiple spatial scales, Journal of Animal Ecology 89, no.22 (Oct 2019): 412–422.https://doi.org/10.1111/1365-2656.13111Fernando A. O. Silveira, Roberta L. C. Dayrell, Cecilia F. Fiorini, Daniel Negreiros, Eduardo L. Borba Diversification in Ancient and Nutrient-Poor Neotropical Ecosystems: How Geological and Climatic Buffering Shaped Plant Diversity in Some of the World’s Neglected Hotspots, (Mar 2020): 329–368.https://doi.org/10.1007/978-3-030-31167-4_14Fabricio Villalobos, Jesús N. Pinto-Ledezma, José Alexandre Felizola Diniz-Filho Evolutionary Macroecology and the Geographical Patterns of Neotropical Diversification, (Mar 2020): 85–101.https://doi.org/10.1007/978-3-030-31167-4_5Y.L. Volpert, E.G. Shadrina Latitude- and climate-associated patterns in small mammal fauna changes of the West Yakutia, Russian Journal of Theriology 18, no.22 (Dec 2019): 99–106.https://doi.org/10.15298/rusjtheriol.18.2.04Zachary W Culumber, Jaime M Anaya-Rojas, William W Booker, Alexandra P Hooks, Elizabeth C Lange, Benjamin Pluer, Natali Ramírez-Bullón, Joseph Travis Widespread Biases in Ecological and Evolutionary Studies, BioScience 69, no.88 (Jul 2019): 631–640.https://doi.org/10.1093/biosci/biz063Boris R. Krasnov, Georgy I. Shenbrot, Natalia P. Korallo-Vinarskaya, Maxim V. Vinarski, Luther van der Mescht, Elizabeth M. Warburton, Irina S. Khokhlova Do the pattern and strength of species associations in ectoparasite communities conform to biogeographic rules?, Parasitology Research 118, no.44 (Feb 2019): 1113–1125.https://doi.org/10.1007/s00436-019-06255-4Lee A Dyer, Matthew L Forister Challenges and advances in the study of latitudinal gradients in multitrophic interactions, with a focus on consumer specialization, Current Opinion in Insect Science 32 (Apr 2019): 68–76.https://doi.org/10.1016/j.cois.2018.11.008Benjamin Yguel, Camille Piponiot, Ariane Mirabel, Aurelie Dourdain, Bruno Hérault, Sylvie Gourlet-Fleury, Pierre-Michel Forget, Colin Fontaine Beyond species richness and biomass: Impact of selective logging and silvicultural treatments on the functional composition of a neotropical forest, Forest Ecology and Management 433 (Feb 2019): 528–534.https://doi.org/10.1016/j.foreco.2018.11.022Brunno F. Oliveira, Brett R. Scheffers Vertical stratification influences global patterns of biodiversity, Ecography 42, no.22 (Aug 2018): 249–249.https://doi.org/10.1111/ecog.03636Tana E. Wood, Molly A. Cavaleri, Christian P. Giardina, Shafkat Khan, Jacqueline E. Mohan, Andrew T. Nottingham, Sasha C. Reed, Martijn Slot Soil warming effects on tropical forests with highly weathered soils, (Jan 2019): 385–439.https://doi.org/10.1016/B978-0-12-813493-1.00015-6Werner Armonies Uncharted biodiversity in the marine benthos: the void of the smallish with description of ten new Platyhelminth taxa from the well-studied North Sea, Helgoland Marine Research 72, no.11 (Nov 2018).https://doi.org/10.1186/s10152-018-0520-8Xoaquín Moreira, William K. Petry, Kailen A. Mooney, Sergio Rasmann, Luis Abdala-Roberts Elevational gradients in plant defences and insect herbivory: recent advances in the field and prospects for future research, Ecography 41, no.99 (Feb 2018): 1485–1496.https://doi.org/10.1111/ecog.03184Amy Berkov Seasonality and Stratification: Neotropical Saproxylic Beetles Respond to a Heat and Moisture Continuum with Conservatism and Plasticity, (May 2018): 547–578.https://doi.org/10.1007/978-3-319-75937-1_16Quentin D. Read, Benjamin Baiser, John M. Grady, Phoebe L. Zarnetske, Sydne Record, Jonathan Belmaker Tropical bird species have less variable body sizes, Biology Letters 14, no.11 (Jan 2018): 20170453.https://doi.org/10.1098/rsbl.2017.0453Christophe Lemetre, Jeffrey Maniko, Zachary Charlop-Powers, Ben Sparrow, Andrew J. Lowe, Sean F. Brady Bacterial natural product biosynthetic domain composition in soil correlates with changes in latitude on a continent-wide scale, Proceedings of the National Academy of Sciences 114, no.4444 (Oct 2017): 11615–11620.https://doi.org/10.1073/pnas.1710262114