|
Expanding grassy ecosystems through the late Cenozoic may have driven ecological and evolutionary change in hominins and other African mammals. However, we lack a sufficiently robust quantitative framework to understand how species should respond to changing vegetation structure or the magnitude of change needed to drive range shifts, speciation, extinction, or adaptation. A more detailed understanding of present-day species-environment relationships at scales appropriate to paleoenvironmental records can help build this framework. Here, we use generalized additive models to estimate modern-day herbivore responses to woody cover gradients across 100+ present-day African parks and reserves. We examine these responses for 58 herbivore species (Artiodactyla, Perissodactyla, Proboscidea) and with species aggregated by tribe (for Bovidae) and dietary functional group (browser, grazer, mixed feeder, frugivore). At the spatial scales of our analysis (i.e., parks and reserves measuring ∼500–5000 km2), we find that few species have strong associations with open (<0.3 fraction woody cover) or closed (>0.7 fraction woody cover) environments. Most herbivores demonstrate a peak probability of presence around 0.5 fraction woody cover. The latter result is consistent with the ecological conditions previously shown to maximize herbivore diversity. At landscape-to-ecosystem spatial scales (102–103 km2 ), which average across finer-scale patches of distinct vegetation types (e.g., grassland, woodland, forest), our results indicate that a taxonomically and ecologically diverse group of species are expected to co-occur. We argue that spatiotemporal scale likely accounts for the ubiquity of mosaic habitat reconstructions in time-averaged fossil assemblages from the late Cenozoic of Africa. In addition, we propose that species' broad tolerances for gradients in woody cover renders the expansion of C 4-dominated ecosystems an uncertain driver of macroevolutionary change (i.e., speciation and extinction) in Africa through the Plio-Pleistocene. Introduction The expansion of C4-dominated ecosystems is one of the most significant paleoenvironmental changes observed in Africa during the late Cenozoic (Levin, 2015). Following the initial appearance of locally abundant C4 grasses in the Early Miocene of eastern Africa (∼21–16 Ma; Peppe et al., 2023), terrestrial and marine paleoenvironmental archives from across the continent broadly document increasing grassy cover over the last ∼10 million years (deMenocal, 2004; Bonnefille, 2010; Cerling et al., 2011; Levin et al., 2011; Dupont et al., 2013; Polissar et al., 2019). This trend is thought to have played a central role in the evolutionary history of African mammals. In particular, research links the expansion of grassy ecosystems to long-term changes in mammal community structure (Reed, 1997; Bobe et al., 2002; Bobe and Behrensmeyer, 2004), pulses of faunal turnover (Vrba, 1985, Vrba, 1992), and dietary changes within multiple mammalian lineages (Uno et al., 2011; Cerling et al., 2015), as well as the emergence of novel adaptations and macroevolutionary changes within the hominin clade (Dart, 1925; Stewart, 2014; Wheeler, 1992; Fillion and Harrison, 2023). This research has fueled the recovery of increasingly detailed records of late Cenozoic paleoenvironments in Africa (e.g., Levin et al., 2004, Levin et al., 2011; Wynn, 2004; Cerling et al., 2011; Lupien et al., 2021; Muiruri et al., 2021; Trauth et al., 2021; Cohen et al., 2022). The importance of paleoenvironmental change to hypotheses about the ecological and evolutionary history of African mammals requires a robust understanding of species-environment relationships in the present day. Foundational paleoecological work helped to link the taxonomic and functional composition of present-day mammal communities to the environments in which they are found (Andrews et al., 1979; Vrba, 1980; Reed, 1998), providing a valuable tool for paleoenvironmental reconstruction (Reed, 2008; Faith and Lyman, 2019). However, as researchers continue to develop detailed records of vegetation change through time (e.g., Levin et al., 2011; Uno et al., 2016; Kinyanjui et al., 2021), including quantitative estimates of woody cover (Cerling et al., 2011; Quinn et al., 2013; Quinn and Lepre, 2021), it is becoming clear that a more detailed understanding of present-day species-environment relationships, on scales relevant to the fossil record, is needed. This is exemplified by recent debate and uncertainty over how, if at all, empirically documented vegetation shifts were likely to have influenced fossil hominins and other mammalian taxa (Patterson et al., 2022; Quinn and Lepre, 2021, Quinn and Lepre, 2022) and by new research questioning assumptions about community-environment relationships in present-day African ecosystems (Negash and Barr, 2023). We aim to build on the current understanding of how African mammals relate to their environments, to strengthen the uniformitarian framework that allows researchers to reconstruct paleoenvironmental change from faunal assemblages, and to infer how paleoenvironmental changes influenced fossil species. Drawing from a database of 58 extant herbivore species from 123 African parks and reserves (Kamilar et al., 2015; Rowan et al., 2016), we use generalized additive models (GAM) to quantify how species respond to gradients in woody cover. We then (i) examine how these responses vary across different species, bovid tribes, and dietary functional groups, and (ii) examine how this framework can enhance our understanding of late Cenozoic fossil assemblages in Africa. Section snippets Species and environmental datasets To model how species occurrences relate to variation in woody cover, our analysis utilizes observations on the presence or absence of African mammals paired with satellite image measurements of vegetation structure. We draw from a previously compiled dataset (Kamilar et al., 2015; Rowan et al., 2016) of taxonomic presence-absences for 160 mammalian species from 123 national parks and game reserves across sub-Saharan Africa (hereafter, we refer to each park or reserve as a “community”) (Fig. 1B) Results Based on our individual GAMs for all herbivore species ( n = 58), 23 had statistically significant responses at the p < 0.001 level, and 36 had significant responses at the p < 0.05 level. This includes 6/10 browsers, 8/10 frugivores, 8/14 mixed feeders, and 14/24 grazers with a statistically significant at p < 0.05. The likelihood r2 values range from 0.05 to 0.52 for statistically significant (p < 0.05) models. The importance of scale Because ecological patterns and processes depend on the spatiotemporal scales of observation (Faith et al., 2021; Levin, 1992; Wiens, 1989), we first consider how spatial scale has shaped our observations. The modern communities analyzed here represent the taxa present across large spatial scales: the interquartile range of areas for the modern communities is 480–5093 km2. These large areas encompass large spatial variation in f wc and can include smaller-scale patches of grassland, woodland, Conclusion We examine how present-day herbivore species respond to gradients in woody cover to strengthen existing frameworks for interpreting the late Cenozoic fossil record in Africa. Paleoecological studies that utilize fossil herbivores to reconstruct past vegetation often derive interpretations from assumptions about the modern-day ecology of different species, tribes, or functional groups—e.g., that wildebeest, alcelaphins, or grazers are indicative of open grasslands. However, our results show that Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments We thank Kaedan O'Brien, the University of Utah Archaeological Center, and two anonymous reviewers for valuable feedback on earlier drafts. KGS was supported in part by a National Science Foundation (NSF) grant to JTF ( 2224318 ) and by a NSF Graduate Research Fellowship # 2023319052 . AD thanks CSU's Vice President for Research's office for funding. References (95) E.V. Bärmann et al. A revised phylogeny of Antilopini (Bovidae, Artiodactyla) using combined mitochondrial and nuclear genes Mol. Phylogenet. Evol. (2013) W.A. Barr et al. Mammal functional diversity and habitat heterogeneity: Implications for hominin habitat reconstruction J. Hum. Evol. (2020) R. Bobe et al. The expansion of grassland ecosystems in Africa in relation to mammalian evolution and the origin of the genus homo Palaeogeogr. Palaeoclimatol. Palaeoecol. (2004) R. Bobe et al. Faunal change, environmental variability and late Pliocene hominin evolution J. Hum. Evol. (2002) R. Bonnefille Cenozoic vegetation, climate changes and hominid evolution in tropical Africa Glob. Planet. Chang. (2010) L. Citores et al. Modelling species presence–absence in the ecological niche theory framework using shape-constrained generalized additive models Ecol. Model. (2020) P.B. deMenocal African climate change and faunal evolution during the Pliocene-Pleistocene Earth Planet. Sci. Lett. (2004) D. de Ruiter et al. Faunal assemblage composition and paleoenvironment of Plovers Lake, a Middle Stone Age locality in Gauteng Province, South Africa J. Hum. Evol. (2008) L.M. Dupont et al. Miocene to Pliocene changes in south african hydrology and vegetation in relation to the expansion of C4 plants Earth Planet. Sci. Lett. (2013) J.T. Faith et al. Rethinking the ecological drivers of hominin evolution Trends Ecol. Evol. (2021) E.N. Fillion et al. Mixed models elucidate local- and regional-scale drivers of paleoenvironmental change in eastern Africa during the emergence of Paranthropus and homo Palaeogeogr. Palaeoclimatol. Palaeoecol. (2023) A. Guisan et al. Generalized linear and generalized additive models in studies of species distributions: setting the scene Ecol. Model. (2002) N.E. Levin et al. Paleosol carbonates from the Omo Group: Isotopic records of local and regional environmental change in East Africa Palaeogeogr. Palaeoclimatol. Palaeoecol. (2011) N.E. Levin et al. Isotopic evidence for Plio-Pleistocene environmental change at Gona, Ethiopia Earth Planet. Sci. Lett. (2004) R.L. Lupien et al. Eastern african environmental variation and its role in the evolution and cultural change of homo over the last 1 million years J. Hum. Evol. (2021) V.M. Muiruri et al. A million year vegetation history and palaeoenvironmental record from the Lake Magadi Basin, Kenya Rift Valley Palaeogeogr. Palaeoclimatol. Palaeoecol. (2021) R. McCleery et al. Animal diversity declines with broad-scale homogenization of canopy cover in african savannas Biol. Conserv. (2018) E.W. Negash et al. Paleodietary reconstruction using stable isotopes and abundance analysis of bovids from the Shungura Formation of South Omo, Ethiopia J. Hum. Evol. (2015) E.W. Negash et al. Relative abundance of grazing and browsing herbivores is not a direct reflection of vegetation structure: Implications for hominin paleoenvironmental reconstruction J. Hum. Evol. (2023) K. O’Brien et al. Paleoecological evidence for environmental specialization in Paranthropus boisei compared to early homo J. Hum. Evol. (2023) R. Potts Hominin evolution in settings of strong environmental variability Quat. Sci. Rev. (2013) R.L. Quinn et al. Pedogenic carbonate stable isotopic evidence for wooded habitat preference of early Pleistocene tool makers in the Turkana Basin J. Hum. Evol. (2013) K.E. Reed Early hominid evolution and ecological change through the African Plio-Pleistocene J. Hum. Evol. (1997) K.E. Reed Paleoecological patterns at the Hadar hominin site, Afar Regional State, Ethiopia J. Hum. Evol. (2008) S.C. Reynolds et al. Landscapes and their relation to hominin habitats: Case studies from Australopithecus sites in eastern and southern Africa J. Hum. Evol. (2011) K.M. Stewart Environmental change and hominin exploitation of C4-based resources in wetland/savanna mosaics J. Hum. Evol. (2014) D.F. Su et al. Mosaic habitats at Woranso-Mille (Ethiopia) during the Pliocene and implications for Australopithecus paleoecology and taxonomic diversity J. Hum. Evol. (2022) M.H. Trauth et al. Recurring types of variability and transitions in the ∼620 kyr record of climate change from the Chew Bahir basin, southern Ethiopia Quat. Sci. Rev. (2021) P.E. Wheeler The thermoregulatory advantages of large body size for hominids foraging in savannah environments J. Hum. Evol. (1992) S.N. Wood et al. GAMs with integrated model selection using penalized regression splines and applications to environmental modelling Ecol. Model. (2002) P. Andrews et al. Patterns of ecological diversity in fossil and modern mammalian faunas Biol. J. Linnean Soc. (1979) L.C. Bishop Suidae R. Bobe Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin Evol. Anthropol. Issues News Rev. (2011) R. Bobe et al. Responses of african bovids to Pliocene climatic change Paleobiol. Mem. (2001) R. Bobe et al. Ecology of Plio-Pleistocene Mammals in the Omo—Turkana Basin and the Emergence of homo Vertebr. Paleobiol. Paleoanthropol. (2009) L.S. Broomhall et al. Home range and habitat use by cheetahs (Acinonyx jubatus) in the Kruger National Park J. Zool. (2003) T.E. Cerling et al. Dietary changes of large herbivores in the Turkana Basin, Kenya from 4 to 1 Ma Proc. Natl. Acad. Sci. USA (2015) T.E. Cerling et al. Woody cover and hominin environments in the past 6 million years Nature (2011) A.S. Cohen et al. Reconstructing the Environmental Context of Human Origins in Eastern Africa through Scientific Drilling Annu. Rev. Earth Planet. Sci. (2022) R.A. Dart Australopithecus africanus: the man-ape of South Africa Nature (1925) H.R. Delcourt et al. Quaternary landscape ecology: relevant scales in space and time Landsc. Ecol. (1988) A. Du et al. Spatial, temporal and taxonomic scaling of richness in an eastern african large mammal community Glob. Ecol. Biogeogr. (2018) J.T. Faith et al. Paleozoology and Paleoenvironments (2019) J.T. Faith et al. Early hominins evolved within non-analog ecosystems Proc. Natl. Acad. Sci. USA (2019) C.S. Feibel Stratigraphy and depositional setting of the Pliocene Kanapoi Formation, lower Kerio valley, Kenya Nat. Hist. Mus. Los Angeles County Contrib. Sci. (2003) M. Gagnon et al. Dietary preferences in extant african bovids J. Mammal. (2000) S.P. Good et al. Climatological determinants of woody cover in Africa Proc. Natl. Acad. Sci. USA (2011) View more references Cited by (0) Recommended articles (6) Research article Macroscopic carbonaceous compression fossils from the Tonian Liulaobei Formation in the Huainan region of North China Precambrian Research, Volume 393, 2023, Article 107076 Show abstract Macroscopic carbonaceous compression fossils are key to understand the early evolution of eukaryotes, explore the development of multicellularity, and strengthen the basis of biostratigraphic correlation during the Tonian Period (ca. 1000–720 Ma). Despite the potential geobiological importance of early macrofossils, the fossil record of Tonian macro-organisms is rarely documented. Here we describe an assemblage of diversified carbonaceous macrofossils from the Tonian Liulaobei Formation in the Huainan region, North China. In this study, we examine a large population of these macrofossils, clarify their taxonomy, and tentatively interpret their phylogenetic affinities. This assemblage consists of thirteen distinct morphotaxa, including eight genera and three new species, showing remarkable taxonomic diversity and domination of coenocytic macroalgae. The new data improve our knowledge about early Neoproterozoic biodiversity, and indicate a Tonian increase in morphological and taxonomic diversity of macrofossils compared to the Mesoproterozoic Era. This study also suggests that macroalgae may have begun to diversify and played a crucial ecological role in Tonian marine ecosystems. Research article Hydrodynamics as a hidden abiotic factor constraining Ordovician chitinozoan morphological evolution Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 621, 2023, Article 111568 Show abstract The Great Ordovician Biodiversification Event (GOBE) was one of the most important macro-evolutionary events of the early Paleozoic, and involved diversification of several planktic groups. Although hydrodynamics must have affected the evolution of these groups, it is difficult to establish causality with confidence. Chitinozoans, mysterious fossils with simple morphology and biostratigraphic utility, underwent great morphological innovations and adaptions through the Ordovician Period, and thus are especially suitable for exploring the effects of hydrodynamics on morphological diversification. We constructed simplified computer models of 92 Ordovician chitinozoan species from major paleoplates to assess the long-term changes in hydrodynamic properties (outer-wall pressure fields and velocity fields) by using computational fluid dynamics. The pressure difference between both ends of the chitinozoan vesicle is suggested to represent the floating ability of the chitinozoan. During the Ordovician, the pressure difference exhibited diachronous fluctuations in different families and on different paleoplates. A continuous increasing passive floating ability was achieved by the Desmochitinidae since the beginning of Ordovician. This evolutionary tendency is consistent with the previously suggested planktonic diversity increase during the GOBE, which initiated since the earliest Ordovician and indicates that the GOBE involved both long-termed taxonomic and morphological radiations. The low-velocity region at the antiapertural part of the vesicle in both individual and chain-structured chitinozoans supports the hypothesis that chitinozoans are independent protists, rather than metazoan eggs. We also analyzed how the evolution of structural innovations, such as chamber shape, neck length, carina length, and ornamentation arrangement, were influenced by hydrodynamics within individual lineages. The results show that several chitinozoan lineages evolved toward increased stability and better floating ability, indicating that convergent evolution in chitinozoans occurred as a result of hydrodynamic pressure. This study highlights the importance of hydrodynamic constraints for the evolution of Ordovician microplankton. Research article Miocene squirrels from Linxia Basin, Gansu, China; paleoenvironmental and palaeoecological implications Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 619, 2023, Article 111530 Show abstract This paper presents the Miocene squirrels of the Linxia Basin in Gansu Province, and a paleoenvironmental and palaeoecological analysis based on the remains collected recently by screen-washing nine localities of early to late Miocene age. The assemblages contain 12 sciurid species (nine genera, three subfamilies), including squirrels with different adaptations, predominantly ground squirrels and chipmunks. Our analysis suggests that Miocene squirrels in Linxia reflect a relatively dry climate and open shrub-steppe environment, and favorable dispersal across Eurasia. The Linxia Miocene squirrels show close taxonomic composition with contemporary faunas known from the Mongol-Xinjiang highland and adjacent regions, implying that northern China represents a single biotic province with uniform paleoenvironment. In addition, the Linxia squirrels are quite different from those found in Yunnan in southern China, which are dominantly tree and flying squirrels that suggest a humid forest biotope. The differences in distribution indicate that Miocene squirrel faunas of China showed distinct provinciality and latitudinal ecological variation. Already in the Miocene we see evidence for predecessors of the present-day Palearctic and Oriental zoogeographic provinces of North and South China. Research article No (Cambrian) explosion and no (Ordovician) event: A single long-term radiation in the early Palaeozoic Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 623, 2023, Article 111592 Show abstract The Cambrian ‘Explosion’, located by many authors between 540 and 520 million years ago (Ma), is considered to be an abrupt appearance in the fossil record of most animal phyla, with a sudden increase of complex morphologies across metazoan groups. In a few recent papers, the Great Ordovician Biodiversification ‘Event’ (GOBE) has similarly been restricted to a single dramatic biodiversification ‘event’ in the Darriwilian Stage of the Middle Ordovician Series, between 470 and 455 Ma, although historically the biodiversification is considered as an aggregation of radiation ‘events’ capturing a large and complex increase of taxonomic diversity of marine invertebrates covering the entire Ordovician. A review of biodiversity curves of marine organisms during the early Palaeozoic, including some based on data in the Paleobiology Database (PBDB) and the Geobiodiversity Database (GBDB), points towards a single, large-scale, long-term early Palaeozoic radiation of life that already started in the late Precambrian. An abrupt ‘explosion’ of diversity in the Cambrian or a significant ‘event’ in the Ordovician are not visible in our biodiversity studies, because they are either regional, or only reflect a single group of organisms. It is evident that the datasets remain incomplete, in particular those for many geographical areas and for several fossil groups, that are not covered by the PBDB and GBDB; also, such areas remain so far poorly or entirely unstudied. Some recently published biodiversity curves have to be considered with care, as the truly global diversity estimates of marine organisms during the early Palaeozoic remain elusive. Here, we argue that published curves of taxonomic richness, which show distinct periods of diversification, cannot sufficiently be disentangled from biases. We therefore question the existence of a distinct Cambrian ‘Explosion’ and global Ordovician ‘Event’ in the global datasets. Both terms, Cambrian ‘Explosion’ and Great Ordovician Biodiversification ‘Event should be used as conceptional terms only. The first represents the appearance of almost all animal phyla during the late Precambrian and early Cambrian, whereas the second term embraces the numerous and complex radiations that occurred during the entire Ordovician. Research article Relative abundance of grazing and browsing herbivores is not a direct reflection of vegetation structure: Implications for hominin paleoenvironmental reconstruction Journal of Human Evolution, Volume 177, 2023, Article 103328 Show abstract The diet of fossil herbivores inferred from enamel stable carbon isotopes is often used to make paleoenvironmental reconstructions. While many studies have focused on using environmental indicator taxa to make paleoenvironmental reconstructions, community-based approaches are considered to provide a more complete picture of paleolandscapes. These studies assume that the diet and relative abundance of herbivores are related to the areal extent of different vegetation types on the landscape. Here, we quantitatively test this assumption in 16 modern ecosystems in eastern and southern Africa with a wide range of woody vegetation cover. We conducted a landscape-level spatial analysis of vegetation patterns using a published land cover data set and computed landscape metrics. We compiled data on relative abundance and diet of herbivores inferred from carbon isotope studies for all large herbivores in these ecosystems. We found that despite differences in the total areal extent of different vegetation types, numerous sizable patches of each vegetation type are available in most ecosystems. However, despite variation across the ecosystems examined, grazers are typically the most abundant herbivores even in sites that have a higher proportion of forest and shrub cover. This indicates that the diet and relative abundance of herbivores is not a simple reflection of the total areal extent of vegetation types available on the landscape. The higher proportion of grazers observed in these ecosystems is a result of multiple factors including habitat heterogeneity, differences in biomass turnover rate between grasses and woody vegetation, resource partitioning, and the advantages of group living in open environments. Comparison of diet and relative abundance of herbivores in modern ecosystems to fossil herbivore assemblages shows that very different vegetation regimes can support similar herbivore assemblages. This study has significant implications for paleolandscape reconstructions and cautions against a simplistic wooded vs. grassland paleoenvironmental interpretations based on fossil herbivore assemblages. Research article First occurrence of caryocaridids (Crustacea, Phyllocarida) in the Ordovician of North China Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 623, 2023, Article 111638 Show abstract Although caryocaridids experienced a significant biodiversity boost during the Ordovician and spread over broad trans-equatorial areas, they have been rarely reported from Siberia, Tarim and North China. Herein, we describe a new species of caryocaridids, Soomicaris ordosensis sp. nov., from the Upper Ordovician of western Inner Mongolia, China, which represents the first report of caryocaridids from the North China craton and extends the palaeogeographical distribution of caryocaridid phyllocarids to the northwestern margin of the Palaeo-Tethys. Detailed morphological and morphometric studies show that these specimens can be ascribed to different ontogenetic stages. After close inspection, we infer that Soomicaris ordosensis sp. nov. should have experienced a long pre-adult time, with several moulting stages, during which time the posterior margin of carapace gradually extends backward to form the posterodorsal spine, and the posterior margin of carapace gradually transitions from convex, linear, and finally to a rightward-sloping sigmoid curve. The taphonomic features of caryocaridids from the Upper Ordovician in the western Inner Mongolia suggest in-situ and parautochthonous preservation. The carapaces have experienced weak phosphatic mineralization during diagenesis. The Ordovician caryocaridids were most likely stenothermic which preferred to inhabit the cool- to cold-water environments from the upper mesopelagic to the lower epipelagic zones, and showed the polar emergence phenomenon. View full text © 2023 Elsevier B.V. All rights reserved. About ScienceDirect Remote access Shopping cart Advertise Contact and support Terms and conditions Privacy policy We use cookies to help provide and enhance our service and tailor content and ads. By continuing you agree to the use of cookies . Copyright © 2023 Elsevier B.V. or its licensors or contributors. ScienceDirect® is a registered trademark of Elsevier B.V. ScienceDirect® is a registered trademark of Elsevier B.V.
|
