Human impact on small-mammal diversity during the middle- to late-Holocene in Iberia: The case of El Mirador cave (Sierra de Atapuerca, Burgos, Spain)

Abstract

The human impact on the environment in the Holocene has usually been characterized on the basis of palaeobotanical records, but attempts to distinguish the anthropogenic impact from natural events in landscape evolution have been the subject of much debate in recent years. The aim of this paper is to analyse small-mammal diversity and the presence of synanthropic species, whose small size makes them more sensitive to any changes in their environment that may occur. This study has allowed us to characterize palaeoclimatic and palaeoenvironmental changes, recording small changes\ud whether resulting from a human influence or otherwise. Our object of study is El Mirador cave, which has a sequence with a well-documented human occupation extending from 7200 to 3000 cal. BP. The study has led us to differentiate two phases. In one phase, we can see small changes in diversity related to climatic oscillations from ca. 7200 to 6800 cal. BP, while in the second phase, lasting from ca. 6800 to 3000 cal. BP, the changes in diversity and in the assemblage of synanthropic species are associated with human economic strategies. Moreover, we distinguish which kinds of economic activity (crop and livestock farming) have influenced these changes, because some small-mammal species are influenced, positively or negatively, by environmental changes based on crop farming and animal husbandry. All this information is contrasted with other archaeological proxies, such as the large-mammal and palaeobotanical assemblages from El Mirador cave. Furthermore, this integrative analysis has made it possible to identify the existence of altered environments more generally throughout the Iberian Peninsula from ca. 6000 cal. BP. It additionally confirms the theory of low human occupation intensity in the northern Meseta and in high mountainous areas during the early Neolithic

Solving a ‘puzzle’. The global 4.2 ka Bond Event at El Mirador cave (Sierra de Atapuerca, Burgos, Spain) and the importance of small mammal taphonomy to the interpretation of past environments and their climatic controls

“…These taphonomic modifications show relative higher percentages in MIR4 than in MIR5, indicating slightly more humid conditions in the former than in the latter level. The palaeoenvironmental evidence provided by the small mammal taxonomy from MIR5 indicates humid conditions in this level, supported by an increase in open dry landscapes together with a decreased in precipitation values from MIR5 to MIR4 (Bañuls-Cardona et al, 2017a, 2017b).…”

“…According to these authors, in the absence of more profitable prey items, the diet of the eagle owls is mainly composed by microtines, which usually make up 30%–80% of prey numbers (Mikkola, 1983). A detailed inspection of the small mammal species recorded at MIR4 and MIR5 indicates that microtines represent the 54.17% and 79.78% of the prey items, respectively (Bañuls-Cardona et al, 2017a, 2017b; Table 1). Although it is claimed that eagle owls show a generalist feeding behaviour, it is necessary to carefully considered two main biases in its prey assemblages: nocturnal animals are taken more commonly due to its time of hunting activity and animals living in the more open and wetter parts of the owl’s hunting range may be over-represented (Andrews, 1990; Mikkola, 1983; Olsson, 1979).…”

“…Eagle owls still being present in MIR4 where palaeoenvironmental analyses indicate an increase in open dry landscapes to the detriment of open humid ones (Bañuls-Cardona et al, 2017a). This environmental change is also linked to an increase in synanthropic taxa ( Crocidura russula , Microtus arvalis , Microtus ( Terricola ) duodecimcostatus and Eliomys quercinus ) (Table 1) in MIR4 with respect to MIR5 (Bañuls-Cardona et al, 2017b) also supported by pollen remains, which indicate a significant increase in crops around the cave in MIR4 level while in MIR5 the anthropogenic impact on vegetation is scarce (Expósito et al, 2017). The intensification of human activities during the Bronze Age period (MIR4) may have caused a homogenisation of the landscape favouring the dominance of the more generalist and synanthropic species, which became the more accessible prey items surrounding the cave.…”

“…Microfossils were separated from the dry sediment distinguishing between cranial and post-cranial elements. Small mammal cranial remains and some post-cranial diagnostic elements were selected by Bañuls-Cardona et al (2017a, 2017b) with the main purpose of obtaining taxonomic and palaeoecological results. Taxonomic analysis from MIR4 and MIR5 revealed a total of seven different small mammal species (Table 1): Crocidura russula , Sorex gr.…”

“…Taphonomic analyses in this work have been carried out using the samples previously sorted by Bañuls-Cardona et al (2017a, 2017b) considering both, cranial and post-cranial small mammal elements. All the fossil materials were studied at the Micropalaeontology laboratory of the Catalan Institute of Human Palaeoecology and Social Evolution (IPHES), where they are housed.…”