Radiocarbon date frequencies through time provide another relative indicator of human population changes

through time. A plot of all dated components from the Northern Channel Islands through 2006 suggests that Native American populations remained relatively steady through much of the Holocene, with a dramatic increase in human populations around A.D. 500 followed by a decline during the Medieval Climatic Anomaly, an increase after about A.D. 1300, and a decline at European Contact (Fig. 2a; Culleton et al., 2006). Far fewer people occupied the islands during the ranching period, but livestock numbered in the hundreds to tens of thousands, leaving a devastating and lasting impact on Bortezomib supplier the landscape. These demographic trends form the background for understanding human environmental impacts through time, and suggest that archeologically we should expect some of the most dramatic changes during the last 3000 years, especially after 1500 years ago when human populations were at their height (Erlandson et al., 2009 and Braje, 2010). Near shore marine ecosystems around the Channel Islands were a focus of human subsistence learn more since colonization and recent research documents a range of impacts that

Native Americans had on island marine organisms including shellfish, marine mammals, and finfish. Erlandson et al., 2008, Erlandson et al., 2011a and Erlandson et al., 2011b measured thousands of California mussel (Mytilus californianus), red and black abalone (Haliotis Terminal deoxynucleotidyl transferase rufescens and H. cracherodii), and owl limpet (Lottia gigantea) shells, documenting size changes in each of these taxa across the Holocene. Average size distributions for California mussels, red abalones, and owl limpets each document size

declines through time ( Fig. 2b), with the steepest declines occurring during the Late Holocene when human populations were also at their zenith ( Erlandson et al., 2008, Erlandson et al., 2011a and Braje et al., 2009). These size distributions were also plotted against a fine-grained record of sea surface temperature and marine productivity, which suggests little correlation to natural climatic changes and human predation as the driving force for these reductions (see also Thakar, 2011). Raab (1992) also demonstrated a pattern of resource depression through time on San Clemente Island as people switched from higher ranked black abalones to smaller black turban snails (Chlorostoma funebralis) and there is evidence for possible human overexploitation of Pismo clams (Tivela stultorum) on Santa Cruz Island ( Thakar, 2011). Humans also appear to have influenced the demographics and abundance of seals and sea lions (pinnipeds).