Impact of climate crisis on mammals largely unknown as scientists sound alarm over huge data gap

There are around 6,400 known species of mammal living across our planet in every kind of landscape and habitat, but scientists have warned that our uneven knowledge of many animals is leaving them vulnerable as the climate crisis worsens.

Nearly 25 per cent of all mammal species are already threatened with extinction, and the risk is exacerbated by climates changing around the world.

However, the myriad ways in which the changes are currently impacting animals, and how they will develop into the future, are highly complex topics, and scientists are sounding the alarm bell over our lack of data and limited knowledge of these interacting systems.

A new review of existing data by a global team of researchers from 15 different institutions has found that most studies examining terrestrial mammals tend to have limited focus and are potentially not showing the full picture of climate change impacts.

Different environmental changes have multiple, and potentially contrasting, effects on various aspects of animals’ lives – such as reproduction and survival, otherwise known as demographic rates.

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In a search of 5,728 terrestrial mammal species, the researchers found just 106 studies that looked at both survival and reproduction at the same time. These covered 87 species, representing less than 1 per cent of all terrestrial mammals.

Dr Maria Paniw from the University of Zurich, the lead author of the study, told The Independent: “There is so much we just don’t know well. Can movement mitigate adverse climate effects? Can climate change have severe indirect effects by, for instance, making populations more susceptible to diseases?

“It is important to emphasise that climate change will not affect mammals in isolation. Instead, many mammal populations are already struggling due to human actions, and climate change may be the final nail on the coffin.”

She added: “Researchers often publish results on the effects of climate on survival or on reproduction - and not both.

“Only in rare cases does a climatic variable, say, temperature, consistently negatively or positively affect all studied rates of survival and reproduction.”

Highlighting the complexity of the web of factors at play, and the research deficit scientists are facing, the research team explained that higher temperatures due to the climate crisis could decrease the number of offspring a mammal might have. However, if the offspring have a better chance of survival because of less competition, the population size may not necessarily be affected.

On the other hand, if higher temperatures impact both reproduction and survival, a study of only one of these could underestimate the effects on a population.

For example, the researchers said Svalbard reindeer, which have appeared to be vulnerable to the climate crisis, may actually see their numbers stabilise, while animals such as meerkats, which are well adapted to hot, dry habitats, could see numbers crash.

Dr Paniw told The Independent: “Extreme climate events are projected to increase under climate change, and such events have led to population crashes of reindeer in the past. A recent study – a full life-cycle, long-term demographic study - has shown however that due to density feedbacks and differential effects on age classes, climate change may actually stabilise the reindeer population studied. This is because climate change affects the least resilient age classes and decreases population density and, with it, competition, which in turn allows more resilient age classes to bounce back.”

“However, that does not mean that we overestimate climate change effects on mammals in general. Let’s look at the meerkats as an example: This arid-environment specialist is adapted to extreme weather such as seasonal droughts. But, it has recently been shown that more variable rainfall regimes interacting with generally hotter seasons, as projected under climate change, could potentially really destabilise social groups and the local study population. In other words, compound effects of interacting factors may exacerbate climate risks. This is particularly true in tropical regions, where habitat degradation may severely affect mammals – and combined with climate change may put a lot of pressure on species. But unfortunately, it is exactly in these regions where we have the least data.”

The research also said there was a concerning mismatch between regions where studies on climate change impacts on mammals were taking place, and the regions recognised as being the most vulnerable to climate change.

The researchers warned that this means we currently know very little about the complex climate impacts in the most climate-vulnerable regions of the globe.

“We were surprised by the lack of data on high-altitude (alpine) mammals,” said Dr Paniw.

“Climate change is expected to be very pronounced in higher elevations, and there have been quite a few studies on plants investigating the population-level consequences of range shifts towards higher altitudes with a generally warming climate.

“In our review, we had a few alpine species – for example, yellow-bellied marmots, plateau pikas – but I was expecting a study or two on iconic species such as perhaps snow leopards.

“Maybe even more so, I was expecting more studies on hibernating rodents, and perhaps even bears. As temperatures are warming, cues to wake up after a long winter may come earlier, but that doesn’t mean that food is available once the animals wake up. This can have severe effects on populations.”

The authors said their research highlights the need for more research on mammal populations that accounts for multiple demographic responses across entire lifecycles.

“To inform evidence-based conservation, we need to prioritise more holistic approaches in data collection and integration in order to understand the mechanisms that drive population persistence,” said Dr Paniw.

“There are many reasons why this data isn’t being captured. An important aspect is that collecting such data requires long-term investment without immediate returns, which has not been favoured by many funding agencies and is also logistically challenging. These challenges are compounded in climate-vulnerable regions, which include many countries with underfunded infrastructure for long-term ecological research.”

The study also raises serious concerns that there are even bigger data gaps for animal groups that are less well studied than terrestrial mammals, such as insects and amphibians.

Such data is urgently needed to inform which species are most vulnerable to climate-driven extinction.

“We must start new collaborations, gather existing and collect new data in climate-vulnerable regions such as the tundra, seasonal tropical forests, the Mediterranean,” said Dr Paniw.

“And we must also focus on different taxa – bats, for instance, where we have very little data, or hibernating mammals.”

The research is published in the British Ecological Society’s Journal of Animal Ecology.