Based on this paper, it seems clear that some non-local people moved in to the Spanish plateau region during the Beaker period, however isotopes wouldn't necessarily show this since most people who live in a region were born there, regardless of their heritage.
In any case, the authors speculate on origins of the foreigners. Unfortunately, it's PPV.
Diet and mobility patterns in the Late Prehistory of central Iberia (4000–1400 cal bc): the evidence of radiogenic (87Sr/86Sr) and stable (δ18O, δ13C) isotope ratiosDíaz-del-Río, P., Waterman, A.J., Thomas, J.T. et al. Archaeol Anthropol Sci (2017). doi:10.1007/s12520-017-0480-y [Link]
This study examines strontium, oxygen, and carbon isotope ratios (87Sr/86Sr, δ18O, δ13C) in dental enamel and bone apatite from 82 individuals interred at Late Neolithic, Chalcolithic, and Bronze Age burial sites near Madrid, Spain, to discern variations in dietary patterns and identify possible migrants. Questions about mobility patterns and subsistence practices have played a central role in the scholarship of Late Prehistoric central Iberia in the last 20 years, but the archaeological record has still not been able to provide clear answers. This study adds valuable data to this line of research. The results of this study suggest that migration from regions with different geologic landscapes was uncommon in these communities. For the identified migrants, based upon the 87Sr/86Sr values, several of the identified non-local individuals originate from regions with substantially older lithological features and possible places of origin are being investigated. As it is not possible to discern individuals who may have moved from regions with similar geologic landscapes using this methodology, these data provide the minimum number of migrants, and it is conceivable that the number of non-locals in this sample may be higher. Combining multiple lines of material and biological evidence and the completion of Sr isotope mapping in the Iberian Peninsula will help to clarify these findings. Stable carbon isotope data provide new and direct evidence of regional changes in consumption patterns. In particular, this study provides some possible evidence for the consumption of C4 plants in third-millennium bc central Spain.