Frédéric Dulude-de Broin: Predators suppress prey reproduction through chronic physiological stress

Frédéric Dulude-de Broin is a wildlife ecologist interested in understanding how predation risk influences individual life-history decisions, affects population dynamic and shapes ecological communities. Frédéric recently completed a master’s degree on the impact of non-consumptive effects of predation on mountain goat reproduction. He is now starting a PhD at Laval University (Québec, Canada) on the role of predation as a driver of arctic terrestrial biodiversity. Here, he discusses his paper “Predation risk and mountain goat reproduction: Evidence for stress-induced breeding suppression in a wild ungulate.

What’s your paper about?

My favorite goat, nanny number 418 behind a rock. Credit Frédéric Dulude-de Broin
My favorite goat, nanny number 418 behind a rock. Credit Frédéric Dulude-de Broin

We studied mountain goats in the foothills of the rocky mountains in Canada. Mountain goats are mainly preyed upon by grizzly bears, cougars and wolves and predation appears to be the main cause of mortality in natural populations of this species. Our paper shows that predators not only kill mountain goats, but also induce chronic physiological stress which then inhibits reproduction.

What is the background behind your paper?

Nanny number 444 surveys the landscape. Credit Frédéric Dulude-de Broin
Nanny number 444 surveys the landscape. Credit Frédéric Dulude-de Broin

The rocky mountain goat population we studied was once the largest in Alberta (Canada). Over the past decade, the population experienced a drastic decline in abundance and fell by more than 80%, potentially because of higher mortality due to predation by grizzly bears, cougars and wolves. Unexpectedly, the proportion of reproductive females, which used to fluctuate around 50%, also dropped and now varies around 20%. We initially thought that poor female body condition might explain the decline in fertility. However, this explanation was unsatisfactory because female mass was higher than average when reproduction was at its lowest. This is when we came up with the idea that the decline in abundance and the decline in reproduction could share a common cause: an increase in predation pressure.

How is your paper new or different from other work in this area?

Wolf on the prowl. Credit Frédéric Dulude-de Broin
Wolf on the prowl. Credit Frédéric Dulude-de Broin

Predation stress has been shown to suppress reproduction in some species like snowshoe hares and seals, but ungulates were thought to avoid chronic stress during episodes of high predation risk by relocating to safer habitats. This ability to spatially mitigate predation risk is likely not possible for mountain goats because they are typically confined to mountain tops. Our results reinforce the idea that species unable to control or predict their exposure to predators are more likely to experience demographic costs of predation risk through stress.

What is the broader impact of your paper (outside of your specific species/study system)

Our study suggests that small isolated populations of long-lived ungulates such as mountain goats or bighorn sheep may be particularly at risk of experiencing stress-related breeding suppression because their ability to avoid a threat by relocating to safer habitats is likely limited. Our results also suggest that factors preventing spatial avoidance of predators like habitat fragmentation could increase the susceptibility of prey to stress-related breeding suppression.

Did you have any problems setting up the experiment/gathering your data?

Wolf spotted near the group of goats. Credit: Frédéric Dulude-de Broin
Wolf spotted near the group of goats. Credit: Frédéric Dulude-de Broin

To quantify stress, I measured metabolites of hormones related to stress in the faeces of marked mountain goats. I needed to know the identity of the goat for each sample in order to account for confounding variables such as age and sex. Therefore, I would sit in the mountain for hours, looking at groups of goats with a spotting scope, waiting for a goat to poop. When that happened, I would quickly take a picture using a 50x camera mounted on a tripod and would wait until the group had left to retrieve the sample of this particular goat. This protocol was quite challenging especially because the steep slopes and rocky ledges where mountain goats hang out are not the most accessible terrain!

What is the best thing about being an ecologist?

For me, the best thing is definitely going to wild places that would be hard to see otherwise and spend time outside in those landscapes. To wake up and get out of your sleeping bag with a group of bighorn sheep hanging out by the cabin; to eat your lunch looking at a pika building its nest; to unexpectedly see wolves coming out of the bush while you are monitoring the goats from a vantage point. This is what keeps me going while working for the following 8 months in an office behind a computer.

Read the paper here and the free plain language summary here.

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