About

Paul L Koch is a Distinguished Professor in the Earth & Planetary Sciences Department at UC Santa Cruz. His expertise lies in isotope biogeochemistry, paleobiology, ecology, and evolution. He is based in the Earth & Marine Sciences building, office A115, and can be contacted via campus email at cpevc@ucsc.edu. Koch's work integrates the study of isotopic compositions to understand biological and ecological processes in the context of Earth's history and evolutionary patterns.

Research topics

• Biology
• Evolutionary biology
• Geography
• Oceanography
• Ecology
• Geology
• Fishery
• Climatology

Selected publications

• Bioenergetic trophic trade‐offs determine mass‐dependent extinction thresholds across the Cenozoic

  Ecology · 2026-05-01

  preprintOpen access

  Body size constrains trophic interactions, shaping the feasibility of species' populations. Over macroevolutionary timescales, these constraints feed back to shape selection on body size and diet. We develop a bioenergetic, three-level trophic framework-typical of terrestrial mammalian ecosystems-to explore how bioenergetic trade-offs emerging from predator-prey interactions constrain coexistence. We show that interactions among predators, prey, and subsidies destabilize populations at both small and large sizes, matching observed limits to predator size and diet. These instabilities constrain coexistence and highlight a feasible predator size range of ca. 40-110 kg, spanning the mean size of terrestrial Cenozoic hypercarnivores. Finally, we show that decreased dietary selectivity confers a fitness advantage to larger carnivores that wanes at the largest sizes, aligning with diet estimates for contemporary and Pleistocene species. Our results underscore that ecological pressures emerging from trophic interactions, rooted in energetics, give rise to selective forces driving observed macroevolutionary patterns.

  PublisherDOI

• Built by Microbes: How Herbivores Thrive on Low-Protein Diets

  Abstracts with programs - Geological Society of America · 2025-01-01

  article
  PublisherDOI

• Reconstructing a Macropredator-Rich Miocene Ocean Using Stable Calcium Isotopes

  Abstracts with programs - Geological Society of America · 2025-01-01

  articleSenior author
  PublisherDOI

• Postglacial Recolonization of the Southern Ocean by Elephant Seals Occurred From Multiple Glacial Refugia

  Global Change Biology · 2025-03-01 · 1 citations

  articleOpen access

  The Southern Ocean is warming more rapidly than other parts of our planet. How this region's endemic biodiversity will respond to such changes can be illuminated by studying past events through genetic analyses of time-series data sets, including historic and fossil remains. Archaeological and subfossil remains show that the southern elephant seal (Mirounga leonina) was common along the coasts of Australia and New Zealand in the recent past. This species is now mostly confined to sub-Antarctic islands and the southern tip of South America. We analyzed ancient seal samples from Australia (Tasmania), New Zealand and the Antarctic mainland to examine how southern elephant seals have responded to a changing climate and anthropogenic pressures during the Holocene. Our analyses show that these seals formed part of a broader Australasian lineage, comprising seals from all sampled locations from the south Pacific sector of the Southern Ocean. Our study demonstrates that southern elephant seal populations have dynamically altered both range and population sizes under climatic and human pressures over surprisingly short evolutionary timeframes for such a large, long-lived mammal.

  PublisherOA PDFDOI

• Body Building with Microbes: Protein Metabolism in Pleistocene Megafaunal Herbivores

  Abstracts with programs - Geological Society of America · 2025-01-01

  article1st authorCorresponding
  PublisherDOI

• Examination of Fe and Cu Isotope Variation in Great Apes Using an Optimized Protocol

  Rapid Communications in Mass Spectrometry · 2025-04-24

  articleSenior author

  ABSTRACT Rationale Iron deficiency plagues reproductive‐aged women across the world, and blood loss during menstruation is proposed as the driving force. To assess if other factors related to reproduction influence Fe and Cu isotope variation in females, we measured Fe and Cu isotope compositions in the bones of chimpanzees and bonobos. Methods To do this, we optimize the protocol for isolating Fe and Cu (and Zn) from phosphate‐rich skeletal materials for further analysis via MC‐ICP‐MS. Then, we address possible Fe and Cu variation sources in non‐menstruating apes ( n = 26, of which the sex of 10 was obtained by DNA analysis). Results The optimized method reduced acid volume by ~14%, and sample preparation time by ~37.5%. We did not find significant sex differences in δ 56 Fe values (Δ 56 Fe f‐m = 0.13‰) or δ 65 Cu values (Δ 65 Cu f‐m = 0.33‰). Conclusion Given the similar Δ 56 Fe f‐m values between non‐menstruating apes and humans, reproductive investment, instead of menstruation alone, is a key factor that drives Fe deficiency in reproductive‐aged women and is important to consider with proxies of iron status. Our optimized protocol provides an effective method for exploring iron status in other mammalian species.

  PublisherDOI

• Author response for "Examination of Fe and Cu Isotope Variation in Great Apes Using an Optimized Protocol"

  2025-02-05

  peer-reviewSenior author
  PublisherDOI

• A centurial signature of anthropogenic nitrogen and carbon in California serpentine ecosystems

  Ecosphere · 2025-02-01

  articleOpen access

  Abstract Increasing anthropogenic emissions of nitrogen (N) and carbon (C) are major threats to ecosystems globally. Although atmospheric N deposition is likely affecting N cycling and community composition in California's serpentine ecosystems, a historical record of N inputs to vegetation has yet to be reconstructed for these nutrient‐limited biodiversity hotspots. For leather oak ( Quercus durata var. durata), a foundational, serpentine‐endemic species, we investigated leaf N and C isotopic composition (δ 15 N and δ 13 C) and leaf %N of herbarium and modern leaf samples collected from 1899 to 2009 from serpentine ecosystems in two study areas in California: Santa Clara County, and Lake and Napa Counties combined. We also evaluated tree ring growth over a similar time period in long‐lived leather oak individuals. Leaf δ 15 N and δ 13 C values decreased over time in both study areas, likely reflecting changes in the regional and local atmospheric N and C pools caused by human perturbation. However, leaf %N values and stem growth did not change over time with increasing N deposition, indicating that increasing atmospheric N deposition and CO 2 concentration may not translate to increased N uptake or productivity in plants with conservative growth strategies, even in ecosystems thought to be N‐limited. In serpentine systems, this could competitively advantage nitrophilic invasive annual grasses and accelerate trends toward native species loss. While the rates of decline in leaf δ 15 N values were similar between study areas, rates of decline in leaf δ 13 C values were steeper in Santa Clara County, possibly reflecting its more urban environment. Herbarium samples combined with tree ring data can provide a valuable opportunity to explore the historical record of human‐induced changes in N and C cycling and their biotic impacts.

  PublisherDOI

• Author response for "Examination of Fe and Cu Isotope Variation in Great Apes Using an Optimized Protocol"

  2025-04-08

  peer-reviewSenior author
  PublisherDOI

• Science at Sundance 2025 <b>Heightened Scrutiny</b> , <i>Sam Feder, director,</i> 2025, 89 minutes. <b>Life After</b> , <i>Reid Davenport, director</i> , 2025, 99 minutes. <b>How to Build a Library</b> , <i>Maia Lekow and Christopher King, directors,</i> Circle and Square Productions, 2025, 103 minutes. <b>SALLY</b> , <i>Cristina Costantini, director</i> , National Geographic, 2024, 103 minutes. <b>The Perfect Neighbor</b> , <i>Geeta Gandbhir, director</i> , 2025, 96 minutes. <b>Middletown</b> , <i>Jesse Moss and Amanda McBaine, directors,</i> 2025, 111 minutes.

  Science · 2025-03-13

  articleOpen access
  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Analysis of a Forty Thousand Year Record of Genetic and Environmental Change in the Arctic

  NSF · $111k · 2004–2007

• Collaborative Research: Spatially Varying Topographic and/or Climatic History of the Sierra Nevada Mountains

  NSF · $99k · 2003–2007

• Collaborative Research: Abandoned Elephant Seal Colonies in Antarctica: Integration of Genetic, Isotopic, and Geologic Approaches toward Understanding Holocene Environmental Change

  NSF · $118k · 2005–2009

• US Egypt Cooperative Research: Baboons, stable isotopes, and the mystery of Punt

  NSF · $73k · 2009–2011

• Collaborative Research: Investigation of Holocene Seasonality and Inter-annual Variability Along the California Current System

  NSF · $190k · 2004–2008

Frequent coauthors

• Gabriel J. Bowen

  University of Utah

  81 shared

• Jin Meng

  72 shared

• André R. Wyss

  University of California, Santa Barbara

  65 shared

• Yaoming Hu

  East China University of Science and Technology

  64 shared

• Marilyn L. Fogel

  University of California System

  55 shared

• Richard W. Carlson

  Planetary Science Institute

  52 shared

• Cynthia F. Moss

  49 shared

• Anna K. Behrensmeyer

  National Museum of Natural History

  49 shared

Education

• Ph.D, Department of Geological Sciences

  University of Michigan

  1989

• M.S., Department of Geological Sciences

  University of Michigan

  1985

• B.A., Department of Geological Sciences

  University of Rochester

  1982

Awards & honors

• Charles Schuchert Award from the Paleontological Society, 19…
• Fellow, Paleontological Society, 2005
• Fellow, Geological Society of America, 2006
• Fellow, California Academy of Sciences, 2013