Why older species may be better survivors

Species don’t all carve out territory the same way. A sweeping analysis across the tree of life shows that, on average, older lineages occupy larger geographical ranges than younger ones.

The relationship isn’t uniform – marine mammals buck the trend, and islands add their own twists – but evolutionary time consistently emerges as a powerful predictor of how far a species spreads.

An international team led by scientists at the German Center for Integrative Biodiversity Research (iDiv), Leipzig University, and the Naturalis Biodiversity Center compared evolutionary age and present-day range size for more than 26,000 species.

A panoramic look across 26,000 species

The dataset spanned seven major groups – birds, reptiles, amphibians, reef fishes, palms, and both terrestrial and marine mammals – providing one of the broadest tests yet of how age shapes distribution.

The headline result is straightforward: older species tend to have larger ranges. That pattern appeared across every group except marine mammals. The logic is intuitive but has not been demonstrated at this scale.

“Older species are expected to have larger distributions because they have had more time, sometimes several millions of years, to expand their ranges since first appearing,” explained first author Adriana Alzate, a scientist at Naturalis.

“Over evolutionary timescales, these species have had more opportunities to reproduce, disperse, colonize, and adapt to diverse environments, allowing them to occupy broader geographical areas.”

Dispersal power changes the pace

Time alone doesn’t tell the whole story. How easily a species moves through landscapes – its dispersal ability – can speed or slow the march outward.

Strong fliers such as birds with long, pointed wings, and plants whose seeds travel with large, wide-ranging animals, often achieve broad ranges quickly. Poor dispersers, including many amphibians, expand more slowly; for them, age exerts a stronger influence because overcoming barriers takes generations.

The study’s cross-taxa lens makes those contrasts visible. Two species of similar age can differ dramatically in range simply because one can vault barriers while the other cannot. That natural experiment plays out worldwide, from continental interiors to archipelagos.

Islands rewrite the rules

Geography sets hard limits, and nowhere is that clearer than on islands. Native species confined to islands necessarily have smaller maximum ranges than their mainland relatives.

The team confirmed that basic constraint, but they also uncovered an unexpected nuance: the gap between young and old species’ ranges is even larger on islands than on continents.

“Island dynamics and ontogeny modulate the relationship between age and range size. Release from predators and competitors may have enabled early island colonizers, typically ecological generalists, to achieve broader ranges than expected based on age only,” said co-author Roberto Rozzi, a scientist at iDIV.

In other words, the first arrivals – often flexible in diet and habitat – can spread widely within the island system, cementing a strong age–range link even under geographic caps.

Why range size matters for survival

Range size isn’t just a biogeographic curiosity; it’s one of the strongest predictors of extinction risk. Species with narrow distributions usually have smaller total populations and fewer local strongholds.

They are more vulnerable to droughts, storms, disease outbreaks, invasive species, and human disturbance. With more than 40,000 species currently facing extinction, understanding what governs range size can sharpen conservation priorities.

That’s especially important as climate change scrambles habitats. If older species generally occupy larger, more environmentally diverse ranges, they may carry genetic variation that helps them cope with shifting conditions.

“This is even more important in the context of changing environmental conditions, because not all species may be able to keep up with these changes,” said senior author Renske Onstein, a biologist at iDIV.

“Possibly, older species have the genetic makeup to more readily adapt and therefore persist in their relatively large ranges. This needs further testing with genetic data, for example, providing exciting possibilities for future research.”

Takeaways for conservation strategies

The study highlights three practical lessons for managers. First, evolutionary age can be a useful flag when assessing exposure to risk: younger, poor-dispersing species with small ranges may need faster, more targeted intervention.

Second, island biotas demand tailored strategies that account for their tight geographic limits and unique dynamics.

Third, bolstering connectivity – through corridors and habitat restoration – can partially compensate for weak dispersal, giving species the chance to expand or shift ranges as climates warm.

Crucially, the work also warns against one-size-fits-all assumptions. Marine mammals, for instance, didn’t follow the main pattern, likely reflecting the fluidity of ocean habitats and the long-distance movements of many whale and dolphin species. The lesson is to treat age as a powerful factor, not a universal rule.

A clock, a map, and a moving target

Range size emerges from the interplay of time, traits, and terrain. Evolutionary “clock time” creates opportunities; dispersal traits determine how readily species seize them; geography dictates what’s possible.

By stitching those pieces together across tens of thousands of species, the researchers show that age leaves a durable imprint on where life lives today.

For conservation in a rapidly changing world, that imprint is more than academic. It helps explain why some species are widespread while their close relatives cling to a single valley or reef.

And it offers a clearer map of where limited resources can do the most good – before small ranges become no ranges at all.

The study is published in the journal Nature Communications.

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