Associate professor


itsuro (at)

Field-based ecology

My main research interest is metapopulation ecology of stream Dolly Varden charr, a salmonid fish. I’ve been monitoring more than 100 local habitats (tributary streams) over 15 years (review in Koizumi 2011). I’m interested in how dispersal affects population dynamics, genetic structure and evolution of life history traits. I also aim to develop research frameworks applicable to other study systems (e.g. Koizumi et al. 2006; Koizumi et al. 2008). Because I was a fisherman (meaning I love fishes!) I’ve studied Dolly Varden from many different viewpoints, such as morphology, behavior and genetics. This provided me with broad concepts and methods for general ecological research, which are applicable to other animals. You can see this from the broad research topics of my students. These topics may appear independent but actually relate to one another. I hope such diversity will produce some novel research questions and theories.


Post Doctoral fellow

Pos doc fellow


PhD student (3+ year)

Personality of red squirrels and adaptation to urbanization

Many wild animals have invaded and adapted to urban areas with the increase in urbanization. Recently it has been understood that such animals have specific behaviors or life histories. I will try to determine why such animals can adapt and how they cope with man-made environments, focusing on the behavior and personality of Eurasian red squirrels. “Be excited with the wonder of animals!!”



Doctor course


PhD student (3+ year)

Population structure of masu salmon in urban cities


Keisuke ATSUMI (CV)

PhD student (3+ year)

Behavioral mechanisms of inter-specific mating

I joined here since 2016 as a PhD course student. My research interests are: (1) function of mutual ornament in Far Eastern daces (genus Tribolodon) and (2) how individual characteristics & conditions affect their propensity for hybridization. I’ve worked on anatomy & conservation genetics on several fishes during BS & MS courses, but I’m broadly interested in ecology & evolution. Experiments are mostly conducted on Far Eastern daces but I’m planning to do experiments also in nine-spine sticklebacks.


Yusaku Ohkubo

PhD student (3+ year)

Statistical modeling in ecology and evolution

Ecologists and evolutionary biologists should not be satisfied only with fieldwork; it’s just a data collection, we need inferences.
However, picking up useful information from noisy and confounding data like we meet is one of the most challenging tasks in statistics. I’m developing methodologies for more credible and accurate inferences in these entangling situations and applying them to real ecological data.



Chris Ayer

PhD student (3rd year)
ayermcg (at)

Effects of ectoparasites on migration behaviour in salmonids

My name is Christopher Ayer, I am a Canadian grad student interested in freshwater parasites and their ecology. This is my first time researching fish and aquatic ecosystems and I’ve learned much in just the few months since my arrival. While this isn’t my first time to Japan, I am thankful for the welcoming attitude of my lab-mates and all the guidance I have received studying here.



Noriyasu Suzuki

PhD student (3rd year)
noriyasu_s_suzuki (at)

Conservation ecology of Golden Venus chub

I am studying the ecology of Golden Venus chub in Shiga prefecture, which is far from Hokkaido. I’d like to attract people’s concern to the tiny, beautiful endangered fish, which should contribute to the conservation.



Jason Anders

PhD student (2nd year)

Urban parasitology in small mammals

I have a deep and passionate love for animals and nature, and want to help protect every bit of it I can before we destroy what little we have left. My current research falls into the realm of Urban Parasitology, an emerging field of study. I’m now investigating how the urban environment affects parasite community and prevalence within wildlife populations. I’m interested in how these changes potentially impact conservation efforts of endangered species as well as human health.

Nature is unimaginably complex, and we as humans tend to forget that we are part of it, that we are another member in the community of organisms. Every time we change or destroy part of it, it affects us, even if we don’t realize it. Therefore, conservation is about far more than just protecting nature simply for its beauty. I can only hope that my research helps to spark a paradigm shift in the way the public views conservation, as well as public policy and urban development so that we can create a more sustainable society that is friendlier to nature.

With elephant

Yuuki Shimamoto

PhD student (1st year)

The effects of domestication on fish: focusing on brain & cognitive abilities

Kanji Tomita (Personal Page)

PhD student (1st year)

Brown bear digging for cicada nymphs

   I’ve been interested in the ecological roles (e.g. ecosystem engineer) of terrestrial animals, especially, the brown bear. In undergrad, I studied on brown bear population trends in northern part of Hokkaido, Japan (as a cooperative research). Since postgraduate course, I’ve studied brown bear digging for cicada nymphs. In the Shiretoko Natural Heritage, eastern part of Hokkaido, brown bears have started digging for cicada nymphs since 2000. I’m investigating the reason why bears start digging for cicada nymphs and their ecological function of soil disturbance. (More details are shown in my personal page.)

  Since 2020, I start another project on belowground species interaction between plant roots and root feeders (e.g. cicada & grub, nematode).

terra incognita” !! (a motto of my former superviser)



Master course

Kenta Nagatsuka

Master student (2nd year)

Theme under construction

My undergraduate major was engineering, but the lectures in ecology I took during my exchange program to Canada fascinated me and led me here Hokkaido. I haven’t decided my thesis yet, but I’m currently interested in social learning and its mechanism in animals. I hope my study here leads to a good and interesting research.



Yasuhiko Otuki

Master student (2nd year)

Interspecific competition between Dolly Varden and white-spotted charr

Hello, I’m Yasu Otsuki. I lived in Nagano prefecture during undergraduate. There are a lot of mountains in Nagano, and I climbed many of them. I’m interested in ecology of freshwater fish, especially salmonid fishes. In Koizumi lab, I will do many fieldworks and I want to learn a lot from wild animals in not only Hokkaido but around the world.



Ayaka Sawada

Master student (2nd year)

Hybridization between native chipmunk and pet-released alien chipmunk


李 瀟園 /Li Xiao yuan (Lily)

Master student (1st year)

Why long-clawed shrew (Sorex unguiculatus) has giant penis?

My research interest is mainly about mammal’s behavioral ecology. Under long time consideration and discussion, now my research project is unraveling the function of long-clawed shrew’s huge penis (almost 40% of its body size!!) and mating behaviors. Why do overwintered sexually matured males have big penis compared with juveniles? How do they use their penis for mating? Have female genital organs co-evolved with males organs? Is male huge penis a trait evolved through sexual selection, or just a case of allometry? How about other shrews’ mating behavior and sexual organs?
  Countless questions need to be answered! I am going to use most of previous data form others and some of new data from myself for statistical analysis. Then, if I am lucky enough for having enough shrews— use them for the experiment: mating behaviors organization.


Ryota Hasegawa

Master student (1st year)

Interactions between parasitic copepods and salmonids

I was studying at the faculty of fisheries when I was an undergraduate student in Hokkaido University, Hakodate. But after bachelor, my passion for “Parasite” brought me to Sapporo again! I’m interested in the interaction between parasitic copepods and their hosts, freshwater salmonids. Furthermore, I’m focusing on the effects of habitat fragmentation by damming. If my research will be useful for their conservation or management, that will be awesome !

Masahiro Naka

Master student (1st year)

Fish and parasite community

I like salmonids and also have interests in parasites, so I’d like to
reveal the hidden interactions among them. I’m looking forward to
studying in Hokkaido especially doing fieldwork, and of course fishing.
P.S. First annual census of Dolly Varden made me exhausted, but the
nature and dollies are very beautiful!!!


Teppei Kimura (Ohdachi lab)

Master student (1st year)

Phytogeography of crayfish worms

I’m interested in the phylogeography, because this analysis shows us the specie’s historical processes. So, I came to Hokudai to study the phylogeographyof crayfish worms that live on the body of endangered Japanese crayfish. I’m excited to conduct field and lab works in the great nature of Hokkaido.

I’ll do my best!!




Past member