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This study seeks to explain how the large herbivore (large vertebrate, megafauna - terrestrial taxa with adults >45 kg) population density changed during abrupt postglacial climate and environmental change. The Lateglacial and Early Holocene (14,600-8300 years ago) were represented by various environmental and climate changes and a transition from a cold to a warm climate, with subsequent changes in flora and fauna. Using Lake Araisi as a case study (Latvia, northeastern Europe), local to regional vegetation was reconstructed by analyzing plant macroremains and pollen from the lake sediment profile. Here, we present the first dung fungus spore based qualitative reconstruction of large herbivore population density from northeastern Europe. Although there was no distinct pattern of large herbivore population variability during the Lateglacial and Early Holocene, higher densities were suggested during warm and relatively stable climatic and environmental conditions. Our findings imply that herbivores did not constantly live at high densities around one lake but rather were dynamic and moved/migrated according to their needs. Because large herbivores reintroduced today live in reserves (commonly fixed areas surrounded by physical borders), they might be more vulnerable to rapid climatic and environmental change compared to those mammals that lived during the Lateglacial and Early Holocene. Hence, they would have only two possible options - adapt or go extinct. (C) 2019 Elsevier B.V. All rights reserved.