The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

Ecological and toxicological effects of inorganic nitrogen pollution in aquatic ecosystems: A global assessment.

(2002). The Effects of Harmful Algal Blooms on Aquatic Organisms. Reviews in Fisheries Science: Vol. 10, No. 2, pp. 113-390.

The Effects of Harmful Algal Blooms on Aquatic Organisms

Genetic studies have typically inferred the effects of human impact by documenting patterns of genetic differentiation and levels of genetic diversity among potentially isolated populations using selective neutral markers such as mitochondrial control region sequences, microsatellites or single nucleotide polymorphism (SNPs). However, evolutionary relevant and adaptive processes within and between populations can only be reflected by coding genes. In vertebrates, growing evidence suggests that genetic diversity is particularly important at the level of the major histocompatibility complex (MHC). MHC variants influence many important biological traits, including immune recognition, susceptibility to infectious and autoimmune diseases, individual odours, mating preferences, kin recognition, cooperation and pregnancy outcome. These diverse functions and characteristics place genes of the MHC among the best candidates for studies of mechanisms and significance of molecular adaptation in vertebrates. MHC variability is believed to be maintained by pathogen-driven selection, mediated either through heterozygote advantage or frequency-dependent selection. Up to now, most of our knowledge has derived from studies in humans or from model organisms under experimental, laboratory conditions. Empirical support for selective mechanisms in free-ranging animal populations in their natural environment is rare. In this review, I first introduce general information about the structure and function of MHC genes, as well as current hypotheses and concepts concerning the role of selection in the maintenance of MHC polymorphism. The evolutionary forces acting on the genetic diversity in coding and non-coding markers are compared. Then, I summarise empirical support for the functional importance of MHC variability in parasite resistance with emphasis on the evidence derived from free-ranging animal populations investigated in their natural habitat. Finally, I discuss the importance of adaptive genetic variability with respect to human impact and conservation, and implications for future studies.

/pdf/the-importance-of-immune-gene-variability-mhc-in-4yulbv2kgg.pdf

The importance of immune gene variability (MHC) in evolutionary ecology and conservation

Sixteen. Postbreeding foraging migrations of northern elephant seals

Necropsy of dead California sea lion (CSL) (Zalophus californianus) pups (n = 20) born in 2014 was done on San Miguel Island, California, in December 2014 and February 2015. The main objective was to obtain data on prevalence/intensity of hookworms (Uncinaria lyonsi) in pups at that time of the year and to compare the results with data from previous studies conducted in December, January, and February. Fourteen dead pups were examined for adult hookworms in December 2014; all pups were infected (prevalence = 100%) with intensity from 6 to 140 (average 58.9 ± 38.9 SD) nematodes per host. Six dead pups were examined in February 2015. Hookworms were present in the intestines of 2 pups (prevalence=33%); two adult female worms were found in each infected pup. From 1 to 23 (average 7.5) parasitic larvae (L3) were found in the blubber of 4 pups. The findings in this study (2014–2015) verify, from earlier observation, that adult U. lyonsi are shed by pups by late February. The prevalence of parasitic L...

https://bioone.org/journals/Comparative-Parasitology/volume-83/issue-2/4824i.1/Hookworms-iUncinaria-lyonsi-i-in-Dead-California-Sea-Lion-iZalophus/10.1654/4824i.1.pdf

Hookworms (Uncinaria lyonsi) in Dead California Sea Lion (Zalophus californianus) Pups and Sand in Winter (2014–2015) on San Miguel Island, California

Abundance of Harbor Seals on San Miguel Island, California, 1927 through 1986

State-based Cormack-Jolly-Seber (CJS) models have become an often used method for assessing states or conditions of free ranging animals through time. Although originally envisioned to account for differences in survival and observation processes when animals are moving though various geographical strata, it has evolved to model vital rates in different life-history or diseased states. We further extend this useful class of models to the case of multivariate state data. Researchers can record values of several different states of interest, e.g., geographic location and reproductive state. Traditionally, these would be aggregated into one state with a single probability of state uncertainty. However, by modeling states as a multivariate vector, one can account for partial knowledge of the vector as well as dependence between the state variables in a parsimonious way. A hidden Markov model formulation allows straightforward maximum likelihood inference. The proposed HMM models are demonstrated with a case study using data from a California sea lion vital rates study.

https://www.biorxiv.org/content/biorxiv/early/2015/08/26/025569.full.pdf

Robert L. DeLong

Papers

Sixteen. Postbreeding foraging migrations of northern elephant seals

Hookworms (Uncinaria lyonsi) in Dead California Sea Lion (Zalophus californianus) Pups and Sand in Winter (2014–2015) on San Miguel Island, California

Abundance of Harbor Seals on San Miguel Island, California, 1927 through 1986

Multivariate State Hidden Markov Models for Mark-Recapture Data

Natural or Anthropogenic