Douglas F. Bertram

Bio: Douglas F. Bertram is an academic researcher from Environment Canada. The author has contributed to research in topics: Population & Seabird. The author has an hindex of 24, co-authored 46 publications receiving 1703 citations. Previous affiliations of Douglas F. Bertram include University of Washington & Simon Fraser University.

Tufted puffin reproduction reveals ocean climate variability

Abstract: Anomalously warm sea-surface temperatures (SSTs) are associated with interannual and decadal variability as well as with long-term climate changes indicative of global warming. Such oscillations could precipitate changes in a variety of oceanic processes to affect marine species worldwide. As global temperatures continue to rise, it will be critically important to be able to predict the effects of such changes on species' abundance, distribution, and ecological relationships so as to identify vulnerable populations. Off the coast of British Columbia, warm SSTs have persisted through the last two decades. Based on 16 years of reproductive data collected between 1975 and 2002, we show that the extreme variation in reproductive performance exhibited by tufted puffins (Fratercula cirrhata) was related to changes in SST both within and among seasons. Especially warm SSTs corresponded with drastically decreased growth rates and fledging success of puffin nestlings. Puffins may partially compensate for within-season changes associated with SST by adjusting their breeding phenology, yet our data also suggest that they are highly vulnerable to the effects of climate change at this site and may serve as a valuable indicator of biological change in the North Pacific. Further and prolonged increases in ocean temperature could make Triangle Island, which contains the largest tufted puffin colony in Canada, unsuitable as a breeding site for this species.

Effects of maternal and larval nutrition on growth and form of planktotrophic larvae

Abstract: Maternal nutritional stress lowers the organic content of eggs and slows the initial growth of larvae of sea urchins and bivalves. Also, larval nutritional stress changes the form and developmental sequence of larvae as an adjustment to scarce food. If effects of nutrient supplies in eggs were like those of nutrient supplies in planktonic food, then maternal nutrition would affect larval form and developmental plasticity in the same way as larval nutrition. We used natural variation in maternal habitat to test this hypothesis, using laboratory growth experiments. In the sea urchin Strongylocentrotus droebachiensis, mothers from greater depth (100 m) had smaller ovaries and smaller eggs than mothers from shallower depth (<6 m), which indicated poorer maternal nutrition at depth. Effects of maternal habitat, gonad size, and egg size on larval growth rate were significant but small compared to the effect of abundance of larval food. The growth of larvae was little affected by differences in maternal habitat that had a large effect on fecundity and some effect on egg size. There were no effects on larval body or juvenile rudiment that resembled the developmental plasticity in response to larval food. Food-limited mothers did not produce larvae with larger larval feeding apparatus or retarded development of juvenile rudiments. Uncoupled morphogenetic effects of endogenous and exogenous nutrients should be advantageous where benthic and planktonic food supplies vary independently. Finely tuned responses to stimuli may restrict the evolutionary consequences of developmental plasticity. Because maternal nutrition did not affect form of the larvae, larval form can be used as an index of planktonic conditions affecting feeding larvae.

Diet reconstruction and historic population dynamics in a threatened seabird

Abstract: 1. For the overwhelming majority of species, we lack long-term information on the dynamics of populations. As a consequence, we face considerable uncertainty about how to discriminate among competing hypotheses of population decline and design conservation plans. 2. The marbled murrelet Brachyramphus marmoratus is a small seabird that nests in coastal old-growth forest but feeds year-round in near-shore waters of the north-eastern Pacific. Although a decline in nesting habitat is the primary reason why marbled murrelets are listed as threatened in Canada, nest predation and food availability may also influence population abundance. To examine the hypothesis that murrelet populations are influenced by variation in diet quality, we analysed stable-carbon and -nitrogen isotopes in feathers of museum specimens collected in the Georgia Basin, British Columbia. 3. Between 1889 and 1996, we found a decline in stable isotopic signatures that was approximately equal to a 62% drop in trophic feeding level. We also found that the estimated proportion of fish in murrelet diet was related closely to murrelet abundance over the past 40 years, as estimated from volunteer surveys. Using these isotopic data, we modelled population size as a function of variation in reproductive rate due to changes in diet quality and found that our model matched closely the 40-year field estimates. We then applied our 107-year isotopic record to the model to back-cast estimates of population growth rate to 1889. 4. Our results suggest that, up to the 1950s, murrelet populations in the Georgia Basin were capable of growing and were probably limited by factors other than diet quality. After this period, however, our results imply that murrelets were often, but not solely, limited by diet quality. 5. Synthesis and applications. Protecting nesting habitat may not be sufficient to rebuild populations of this highly secretive and threatened seabird and recovery might also require the restoration of marine habitat quality, as well as a better understanding of how ocean climate affects prey abundance and reproductive rate. Combined with contemporary demographic data, stable isotope analysis of historic samples provides a unique opportunity to reconstruct population histories for species where we lack long-term information.

Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs

Abstract: Systematic monitoring of seabird populations in Canada has been ongoing since the 1920s and the monitoring of diets and other biological indicators of ecosystem change started in the 1970s. Long-te...

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: 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.

Climate Change Impacts on Marine Ecosystems

Abstract: In marine ecosystems, rising atmospheric CO2 and climate change are associated with concurrent shifts in temperature, circulation, stratification, nutrient input, oxygen content, and ocean acidification, with potentially wideranging biological effects. Population-level shifts are occurring because of physiological intolerance to new environments, altered dispersal patterns, and changes in species interactions. Together with local climate-driven invasion and extinction, these processes result in altered community structure and diversity, including possible emergence of novel ecosystems. Impacts are particularly striking for the poles and the tropics, because of the sensitivity of polar ecosystems to sea-ice retreat and poleward species migrations as well as the sensitivity of coral-algal symbiosis to minor increases in temperature. Midlatitude upwelling systems, like the California Current, exhibit strong linkages between climate and species distributions, phenology, and demography. Aggregated effects may modify energy and material flows as well as biogeochemical cycles, eventually impacting the overall ecosystem functioning and services upon which people and societies depend.

Variation in discrimination factors (Δ15N and Δ13C): the effect of diet isotopic values and applications for diet reconstruction

Abstract: Summary 1The use of stable isotopic techniques to study animal diets and trophic levels requires a priori estimates of discrimination factors (Δ13C and Δ15N, also called fractionation factors), which are the differences in isotopic composition between an animal and its diet. Previous studies have shown that these parameters depend on several sources of variation (e.g. taxon, environment, tissue) but diet as a source of variation still needs assessment. 2We conducted an extensive review of the literature (66 publications) concerning estimates of animal-diet Δ13C (n = 290) and Δ15N (n = 268). We analysed this data set to test the effect of diet isotopic ratio on the discrimination factor, taking into account taxa, tissues, environments and lipid extraction treatments. Our results showed differences among taxonomic classes for Δ13C, but not for Δ15N, and significant differences among tissues for both Δ13C and Δ15N. We found a significant negative relationship between both, Δ13C and Δ15N, with their corresponding diet isotopic ratios. This relationship was found also within taxonomic classes for mammals (Δ13C and Δ15N), birds (Δ13C), fishes (Δ13C and Δ15N) and invertebrates (Δ13C and Δ15N). From these relationships, we propose a method to calculate discrimination factors based on data on diet isotope ratios (termed the ‘Diet-Dependent Discrimination Factor’, DDDF). 3To investigate current practice in the use of discrimination factors, we reviewed studies that used multi-resource isotopic models. More than 60% of models used a discrimination factor coming from a different species or tissues, and in more than 70% of models, only one Δ13C or Δ15N was used for all resources, even if resources had very different isotopic ratios. Also, we estimated DDDFs for the studies that used isotopic models. More than 40% used Δ15N values and more than 33% used Δ13C values differing > 2‰ from estimated DDDFs. 4Synthesis and applications. Over the last decade, applied ecologists have discovered the potential of stable isotopes for animal diet reconstruction, but the successful adoption of the method relies on a good estimation of discrimination factors. We draw attention to the high variability in discrimination factors, advise caution in the use of single discrimination factors in isotopic models, and point to a method for obtaining adequate values for this parameter when discrimination factors cannot be measured experimentally. Future studies should focus on understanding why discrimination factors vary as a function of the isotopic value of the diet.