Dr Chris Oosthuizen, an alumnus of the University of Pretoria (UP)’s Department of Zoology and Entomology and a research associate with UP’s Marion Island Marine Mammal Programme (MIMMP), was recently awarded the Population Ecology Young Author Award. This award recognises early-career authors of the best papers published in the peer-reviewed Population Ecology.

Dr Oosthuizen’s award-winning paper, Individual heterogeneity in life‐history trade‐offs with age at first reproduction in capital breeding elephant seals, stems from his PhD thesis, supervised by Professor Nico de Bruyn with Professors Marthán Bester, Res Altwegg (University of Cape Town) and Marie Nevoux (UMRESE, France) as co-supervisors. He finalised the paper while he was a National Research Foundation Innovation postdoctoral fellow with Prof De Bruyn, the Principal Investigator of the Marion Island Marine Mammal Programme (MIMMP), which is a research programme of UP’s Mammal Research Institute.

“This award highlights the collective efforts of those who have led the MIMMP, and the nearly 100 field assistants who have walked the extra mile to collect demographic data on marine mammals at Marion Island,” Dr Oosthuizen says. “Demographic research on long-lived animals requires long-term data. Our research would have been impossible without the support of funding bodies, and the dedicated work of MIMMP field assistants over a period of nearly 40 years.”

Dr Chris Oosthuizen and his PhD thesis supervisor Professor Nico de Bruyn. 

The Mammal Research Institute formally commenced marine mammal research at Marion Island in 1973, and in 1983 Prof Bester established a long-term capture-mark-recapture study on southern elephant seals with success. Today, this study continues into its thirty-eighth consecutive year, and the dataset comprise nearly 20 000 individually known seals. The ongoing study is globally unique and renowned for its ability to tease apart questions about the population ecology of these large marine predators.

“The broad objective of my postgraduate and postdoctoral research at UP was to investigate how between-individual variation affects the life-history evolution and population demography of southern elephant seals and other long-lived species,” Dr Oosthuizen explains.

“I considered the various investments in growth, reproduction and survivorship that individuals make, and how these life-history tactics correlate with each other. In long-lived species, the evolution of life-history traits, and their influence on population dynamics, are strongly influenced by age effects. It is therefore of great interest to population ecologists to quantify accurately how life-history traits vary with age. This was easy to do with southern elephant seals at Marion Island, as all pups born on the island are uniquely marked with small identification tags, allowing researchers to track their reproduction performance and survival with age. But many other factors may also affect life-history trajectories, which presents the opportunity for selection. Incorporating such individual heterogeneity into our understanding of changes in life-history traits with age is an important goal in population and evolutionary ecology.”

Dr Chris Oosthuizen's current research investigates the foraging behaviour of krill-dependent chinstrap penguin populations in the Antarctic Peninsula, and how these penguins might inform ecosystem-based fisheries management in this part of Antarctica.

In the paper, Dr Oosthuizen and colleagues statistically accounted for unobserved or “hidden” demographic heterogeneity that exists between individuals. “We used finite mixture models to partition individual life-history trajectories into two classes that represent life-history tactics that differ from the mean trajectory of the population. This partitioning enabled us to show that individual heterogeneity governs the expression of trade-offs with first reproduction in elephant seals, with an immediate survival cost of first reproduction present among ‘low quality’ individuals only. This structured life-history differences among individual females from the same population would have gone undetected had we not accounted for hidden demographic heterogeneity in our analyses,” Dr Oosthuizen explains.

“We found that individuals that started to breed earlier in life survive and reproduce better than delayed breeders, which supports the hypothesis that recruitment age is an indicator of individual quality. Typically, these higher-performing females also received better maternal care as pups, meaning that animals which start well continue to benefit from that advantage throughout their lives.”

Dr Oosthuizen has been affiliated to the MIMMP since 2007, when he was a field assistant at Marion Island. Though he remains involved with the MIMMP, he started a new postdoctoral fellowship at the Marine Apex Predator Research Unit at Nelson Mandela University (NMU) earlier this year. His research at NMU investigates the foraging behaviour of krill-dependent chinstrap penguin populations in the Antarctic Peninsula, and how these penguins might inform ecosystem-based fisheries management in this part of Antarctica.

Read more on the history and activities of UP’s MIMMP at www.marionseals.com.

Announcement of the first Population Ecology Award - Population Ecology.