The focus of this research was to determine the intra- and inter-individual isotopic variation in individuals from the Meroitic cemetery 8-B-5.A (350 BC–350 AD) at Sai Island, Sudan and from individuals at Lamanai, Marco Gonzalez, and San Pedro from Postclassic Maya, Belize (1000–1544 AD) to assess usefulness in sorting archaeological and forensic commingled remains. Stable carbon, nitrogen, and oxygen isotope analyses of collagen and carbonate were conducted for all individuals, in addition to radiogenic strontium isotope analysis for individuals from 8-B-5.A. Seven different skeletal elements were sampled from 24 individuals, totaling 170 samples. Ten human and five faunal teeth from Sai Island were sampled for strontium analysis. Carbon isotopes are consistent with previous studies indicating a mixed C3/C4 diet at Sai Island and a predominantly C4 diet at the Maya sites. Strontium analysis indicates that the individuals from cemetery 8-B-5.A were local to the region of Sai Island. Coefficient of variance analysis demonstrated that intra-individual variation of δ13Ccoll and δ15N values at all four sites is dependent on the individual. A MANOVA demonstrated statistically significant differences and discriminant function analysis identified geographic location/diet as the main driver of inter-individual variation. When assessing inter-individual δ13Ccoll and δ15N variation between bone types, the humerus and femur provided the greatest range of isotope variation, suggesting that these two elements may be the best sampling options for commingled remains assessments. While this research assesses the isotopic variation in these populations, this variation may not be consistent across other populations, and the variation for δ13Ccarb and δ18O values is too large to be useful for anthropological applications. Further assessment is needed in skeletal assemblages from different regions, with different diets, between sexes, and varying ages to understand and identify the driving forces of isotopic intra-individual variation.

The work in this thesis deals with the ecology and evolution of adaptive individual variation. Ecologists have long used niche theory to describe the ecology of a species as a whole, treating conspecific individuals as ecological equivalent. During recent years, research about individual variation in diet and morphology has gained interest in adaptive radiations and ecological speciation. Such variation among individual niche use may have important conservation implications as well as ecological and evolutionary implications. However, up to date we know very little about the extension of this phenomenon in natural populations and the mechanisms behind it. The results in this thesis show that the extension of individual diet specialization is widely spread throughout the animal kingdom. The variation in diet is mainly correlated to morphological variation but not always. Furthermore, this variation in diet and morphology among individuals could be both genetically determined and environmentally induced and it mainly comes from trade-offs in foraging efficiency between different prey types. The results from a number of studies of perch also show that individual perch differ in morphology and diet depending on habitat, where littoral perch has a deeper body compared to pelagic perch. This difference in morphology corresponds to functional expectations and is related to foraging efficiency trade-offs between foraging in the littoral and pelagic zone of a lake. The variation in morphology in perch is mainly due to phenotypic plasticity but there are also small genetic differences between the littoral and pelagic perch. Two separate studies show that both predation and competition may be important mechanism for the variation in morphology and diet in perch. In conclusion, the results in this thesis show that individual variation in diet and habitat choice is a common phenomenon with lots of ecological and evolutionary implications. However, there are many mechanisms involved in this phenomenon on which we are just about to start learning more about, and only further research in this area will give us the full insight.

<p>The work in this thesis deals with the ecology and evolution of adaptive individual variation. Ecologists have long used niche theory to describe the ecology of a species as a whole, treating conspecific individuals as ecological equivalent. During recent years, research about individual variation in diet and morphology has gained interest in adaptive radiations and ecological speciation. Such variation among individual niche use may have important conservation implications as well as ecological and evolutionary implications. However, up to date we know very little about the extension of this phenomenon in natural populations and the mechanisms behind it.</p><p>The results in this thesis show that the extension of individual diet specialization is widely spread throughout the animal kingdom. The variation in diet is mainly correlated to morphological variation but not always. Furthermore, this variation in diet and morphology among individuals could be both genetically determined and environmentally induced and it mainly comes from trade-offs in foraging efficiency between different prey types. </p><p>The results from a number of studies of perch also show that individual perch differ in morphology and diet depending on habitat, where littoral perch has a deeper body compared to pelagic perch. This difference in morphology corresponds to functional expectations and is related to foraging efficiency trade-offs between foraging in the littoral and pelagic zone of a lake. The variation in morphology in perch is mainly due to phenotypic plasticity but there are also small genetic differences between the littoral and pelagic perch. Two separate studies show that both predation and competition may be important mechanism for the variation in morphology and diet in perch.</p><p>In conclusion, the results in this thesis show that individual variation in diet and habitat choice is a common phenomenon with lots of ecological and evolutionary implications. However, there are many mechanisms involved in this phenomenon on which we are just about to start learning more about, and only further research in this area will give us the full insight.</p>