Ecosystem productivity affected the spatiotemporal disappearance of Neanderthals in Iberia

What role did fluctuations play in biomass availability for secondary consumers in the disappearance of Neanderthals and the survival of modern humans? To answer this, we quantify the effects of stadial and interstadial conditions on ecosystem productivity and human spatiotemporal distribution patterns during the Middle to Upper Palaeolithic transition (50,000–30,000 calibrated years before the present) in Iberia. First, we used summed probability distribution, optimal linear estimation and Bayesian age modelling to reconstruct an updated timescale for the transition. Next, we executed a generalized dynamic vegetation model to estimate the net primary productivity. Finally, we developed a macroecological model validated with present-day observations to calculate herbivore abundance. The results indicate that, in the Eurosiberian region, the disappearance of Neanderthal groups was contemporaneous with a significant decrease in the available biomass for secondary consumers, and the arrival of the first Homo sapiens populations coincided with an increase in herbivore carrying capacity. During stadials, the Mediterranean region had the most stable conditions and the highest biomass of medium and medium–large herbivores. These outcomes support an ecological cause for the hiatus between the Mousterian and Aurignacian technocomplexes in Northern Iberia and the longer persistence of Neanderthals in southern latitudes.


Statistics
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Software and code
Policy information about availability of computer code Data collection The LPJ-GUESS v4.0 was used to estimate the Net Primary Productivity. LPJ-GUESS can be obtained on request through Lund University (http://web.nateko.lu.se/lpj-guess)

Data
Policy information about availability of data All manuscripts must include a data availability statement. This statement should provide the following information, where applicable: -Accession codes, unique identifiers, or web links for publicly available datasets -A description of any restrictions on data availability -For clinical datasets or third party data, please ensure that the statement adheres to our policy All data generated or analysed during this study are available on Github: https://github.com/ERC-Subsilience/Data-and-code-associated-with-Iberia-Neanderthalecosystems-productivity_Nature-Ecology-Evolution; associated-with-Iberia-Neanderthal-ecosystems-productivity_Nature-Ecology-Evolution: Data-and-code-associated-with-Iberia-Neanderthal-ecosystems-productivity_Nature-Ecology-Evolution. https://doi.org/10.5281/zenodo.6826921)

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Study description
We test whether the temporal and spatial replacement patterns of H. neanderthalensis by H. sapiens in Iberia were affected by alterations in the ecosystem productivity.To this end, we integrated three modelling approaches. First, we built Bayesian age models for each cultural techno-complex in the four biogeographic regions of Iberia. This analysis was performed with the OxCAL4.2 software and the INTCAL20 calibration curve. This chronological assessment was complemented with Optimal Linear Estimation and Summed Calibrated Distribution of dated archaeological assemblages. Second, we used a generalised dynamic vegetation model (LPJ-GUESS v.4) with tested climate inputs from an atmospheric general circulation model to estimate the evolution of Net Primary Productivity (NPP) between 55 and 30 ky BP in each archaeological and paleontological site of the MIS 3. A sensitivity analysis was performed to assess the robustness of the NPP estimations by using the climate inputs obtained from alternative paleoclimatic models. Lastly, we validated a macroecological model against empirical present-day herbivore densities from a broad range of terrestrial ecosystems and used this modelling approach to estimate the herbivore carrying capacity in each stadial and interstadial phase.

Research sample
This study includes the chronometric dates and the herbivore species recovered from 62 archaeological and 7 paleontological sites dated in the MIS 3. We used the climate datasets from the CRU v.4 and the HadCM3B-M2.1 coupled general circulation model to estimate the Net Primary Productivity. The Eurasian Modern Pollen Database v.2 was used to obtain temperature and precipitation transfer functions based on pollen subsets. These predictive functions were applied to the fossil pollen recovered from 93 palynological assemblages from 51 dated archaeological levels from all the biogeographic regions included in this study. The Phylacine dataset was used to obtain the body mass of the herbivore species included in the study. To validate the macroecological model that estimates herbivore abundances, we used data of 516 extant herbivore population densities obtained from the TetraDENSITY database.

Sampling strategy
To our knowledge, this study includes all the archaeological sites of the Middle to Upper Palaeolithic transition in Iberia. A rarefaction test was used to assess the sample size used to reconstruct the paleocommunity composition in each biogeographic region. All data used in this study was compiled from the literature or obtained from the modeling approaches described in the manuscript.

Data collection
Data was collected by Vidal-Cordasco & Marín-Arroyo from the literature.
Timing and spatial scale Archaeo-paleontological data was collected from the literature between 01/04/2021to 01/11/2021. Data from the LPJ-GUESS model was obtained from 01/06/2021 to 01/11/2021. Regarding the spatial scale, data obtained focused in the Iberian Peninsula.

Data exclusions
We excluded from the age models some archaeological levels with cultural or stratigraphic inconsistencies. Some of these exclusion criteria were pre-established (e.g. only included archaeological levels with Mousterian, Châtelperronian or Aurignacian remains were included); however, after performing the sensitivity tests, we decided to exclude all dates obtained from marine shell remains due to the uncertainties with the reservoir effects. The specific rationale behind each exclusion is discussed in Supplementary Note.

Dating methods
Any new date is provided in this study Tick this box to confirm that the raw and calibrated dates are available in the paper or in Supplementary Information.

Ethics oversight
No ethical approval was required Note that full information on the approval of the study protocol must also be provided in the manuscript.