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Evidence record

Why are there more species in the tropics?

Every sentence on the exploration belongs to at least one claim below. Each says what kind of statement it is, what it rests on, what the evidence does not establish, and how far it was checked. Nothing here is a score, and none of it is a verdict on a belief or a theory.

Last checked 24 September 2026.

  • Partly checked: 13
  • Source checked: 32
  • A judgement, not a fact: 7

If something here is wrong, misquoted, out of date or unfair, write to support@unknownoceans.com and give the claim number, which does not change.

What the question takes for granted

A scientific question about a pattern that is measured and an explanation that is not. The pattern is among the best documented in ecology; its cause is argued between several accounts that need not exclude one another.

  • More species live in the tropics than at higher latitudes

    Established

    Established across hundreds of published gradients, with exceptions and with a strength that varies by scale, habitat and region. In the sea, whether richness dips at the equator is argued.

  • There is one cause to find

    Contested

    The question is usually asked as if it had a single answer. A 2019 review calls the leading hypotheses not mutually exclusive, and in mammals different orders reach a tropical peak by different routes.

  • The species counts being compared are complete enough to compare

    Contested

    Tropical groups are the least completely known, which can shape both richness counts and the rates estimated from them.

How the question is labelled

Claim: The oldest pattern in ecology

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

What this does not establish

Rests on the review’s abstract; the historical account in its body was not read. "Oldest" means longest recognised, not oldest in the history of life.

Claim 1 · checked 24 September 2026 · AI-assisted audit

Claim: The tropics

Kind
Framing. Signposting. It asserts nothing a source could check.

The question

Claim: Noticed for two centuries

Kind
Historical claim. A statement about the past that historical evidence can test.
Review
Source checked. The cited passage was read, and it says this.

Claim 3 · checked 24 September 2026 · AI-assisted audit

Claim: true for nearly every group of plants and animals counted

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    On the generality of the latitudinal diversity gradientDiscussion, "The Generality of the Latitudinal Gradient"

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Meta-analysis

    The source reads: The first major conclusion from this general analysis is therefore that the latitudinal decline of diversity is a ubiquitous phenomenon

  • Qualifies

    On the generality of the latitudinal diversity gradientDiscussion

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Meta-analysis

    The source reads: Aquatic macrophytes as a group tend to show significant diversity increases toward the poles

What this does not establish

The meta-analysis covered eukaryotes; about one study in twenty-three found richness rising towards the poles, and water plants as a group do.

Later work looked for

Crossref, 2005 on, "latitudinal diversity gradient meta-analysis": Kinlock and others (2018) confirm the generality with a weaker gradient; nothing that removes the claim.

Corrected

24 September 2026. Previously: “true for nearly every group ever counted” The meta-analysis behind the claim covered eukaryotes only; whether microbes follow the gradient is a separate and contested question.

Claim 4 · checked 24 September 2026 · AI-assisted audit

Claim: and explained by about thirty competing hypotheses

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

What this does not establish

The count depends on how hypotheses are split: one review says over 30, another at least 26. The first was read only as an abstract.

Claim 5 · checked 24 September 2026 · AI-assisted audit

Claim: Species richness rises towards the equator in almost every group on land and at sea

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

Weaker in fresh water than on land or in the sea, and with exceptions.

Later work looked for

Crossref, 2005 on, "latitudinal diversity gradient meta-analysis": Kinlock and others (2018) confirm it across marine and terrestrial realms; nothing that changes it.

Claim 6 · checked 24 September 2026 · AI-assisted audit

Claim: The pattern is among the most robust in biology

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    On the generality of the latitudinal diversity gradientDiscussion

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Meta-analysis

    The source reads: the latitudinal gradient of diversity is highly general and arguably the most common statistical pattern of spatial variation in diversity

Later work looked for

Crossref, 2005 on, "latitudinal diversity gradient meta-analysis": Kinlock and others (2018) find it general but weaker than first estimated; nothing that changes the claim.

Claim 7 · checked 24 September 2026 · AI-assisted audit

Claim: and among the least explained

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Claim 8 · checked 24 September 2026 · AI-assisted audit

Claim: the leading accounts differ on whether the tropics make new species faster, lose them more slowly, or have simply had longer.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Evolution and the latitudinal diversity gradient: speciation, extinction and biogeographyabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The time and area hypothesis holds that tropical climates are older and historically larger ... The diversification rate hypothesis holds that tropical regions diversify faster due to higher rates of speciation ... or due to lower extinction rates.

Claim 9 · checked 24 September 2026 · AI-assisted audit

Claim: Walk one of the richest hectares of Amazon forest, near Iquitos, and you will pass about 300 species of tree at least 10 centimetres thick.

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

  • Supports

    Tree species richness of upper Amazonian forestsabstract

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Research in plants · Measurement

    The source reads: The two plots from the everwet forests near Iquitos, Peru, are the most species-rich in the world, with ≈300 species ≥10 cm diameter in single hectares

What this does not establish

Two plots, censused in the 1980s and then the richest known. The abstract counts all plants of that diameter; the plot tables, which would separate trees from any climbers, are page scans and were not read.

Later work looked for

Crossref, 1990 on, "tree species richness one hectare Amazon plot": the top results were plot inventories elsewhere; nothing found that changes the figure.

Corrected

24 September 2026. Previously: “Walk a hectare of Amazon forest near Iquitos and you will pass about 300 tree species.” The figure is for the two richest plots Gentry censused, not any hectare, and counts only stems at least 10 cm in diameter.

Claim 10 · checked 24 September 2026 · AI-assisted audit

Claim: The whole of Europe has 454 native trees.

Kind
Present-day figure. A count, survey or report finding, as the named source gives it.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    European Red List of Treessection 3.1

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Reference work

    The source reads: In total, there are 454 species of native trees in Europe, found in 45 families.

  • Qualifies

    European Red List of Treessections 2.3 and 3.1

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Reference work

    The source reads: a woody plant with usually a single stem growing to a height of at least two metres ... Rosaceae, which has 216 tree species, the majority of which are from the genus Sorbus ... we have applied the species concept for both sexual and apomictic species

What this does not establish

The IUCN count includes asexual (apomictic) species, most of them in Sorbus, which make up much of the Rosaceae’s 216, and defines a tree by height and habit rather than by stem diameter, so the two figures are not like for like.

Later work looked for

Crossref, 2019 on, "European native tree species red list": nothing that revises the count.

Claim 11 · checked 24 September 2026 · AI-assisted audit

Claim: The gradient is not subtle and it is not in doubt.

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

Not in doubt as a general pattern today; its history in deep time and its shape in the sea are argued (claims 19 and 23).

Later work looked for

Crossref, 2005 on, "latitudinal diversity gradient meta-analysis": Kinlock and others (2018) confirm it; nothing that changes it.

Claim 12 · checked 24 September 2026 · AI-assisted audit

Claim: What produces it has been argued since Darwin and Wallace were alive.

Kind
Historical claim. A statement about the past that historical evidence can test.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Evolution and the latitudinal diversity gradient: speciation, extinction and biogeographyp. 316, "Evolutionary and biogeographical hypotheses – a brief history"

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: Both Darwin (1859) and Wallace (1878) suggested that adaptations in the temperate zone are governed by a harsh climate, while those in tropical regions are caused by biotic interactions

Claim 13 · checked 24 September 2026 · AI-assisted audit

The pattern

Claim: The pattern

Kind
Framing. Signposting. It asserts nothing a source could check.

The pattern is nearly universal

Claim: The pattern is nearly universal

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    On the generality of the latitudinal diversity gradientDiscussion

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Meta-analysis

    The source reads: These few positive gradients remain exceptional, though, and the latitudinal gradient of diversity is highly general

Later work looked for

Crossref, 2005 on, "latitudinal diversity gradient meta-analysis": Kinlock and others (2018) confirm the generality; nothing that changes it.

Claim 15 · checked 24 September 2026 · AI-assisted audit

Claim: Richness increases towards the equator for trees, birds, mammals and molluscs, on land and in the sea.

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

Each group has exceptions: hares and pikas peak in the north among mammals, and the molluscs cited include studies that found the opposite.

Later work looked for

Crossref, 2010 on, "latitudinal gradient extinction rate tropics": Rolland and others (2014) confirm the tropical peak in mammals; nothing that changes the list.

Corrected

24 September 2026. Previously: “Richness increases towards the equator for trees, birds, mammals and marine molluscs, on land and in the sea.” The meta-analysis names molluscs among the groups with strong declines but does not say the molluscs in question are marine; the marine realm is carried separately, by its comparison of marine and terrestrial gradients.

24 September 2026. Previously: “Richness increases towards the equator for trees, insects, birds, mammals and marine molluscs, on land and in the sea.” No source read carries insects as a group, and ichneumonid wasps are the classic case where the gradient is absent.

Claim 16 · checked 24 September 2026 · AI-assisted audit

Claim: A meta-analysis of nearly 600 published gradients found the decline holds across organisms, habitats and regions, more strongly at regional scales than at local ones.

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

The strength of the decline varied: it was weaker in fresh water and differed between continents. A 2018 reanalysis with newer methods found the gradient general but weaker.

Later work looked for

Crossref, 2005 on, "latitudinal diversity gradient meta-analysis": Kinlock and others (2018), 389 gradients since 2003, confirm the generality with smaller effects; recorded as qualifying.

Claim 17 · checked 24 September 2026 · AI-assisted audit

Claim: It reaches back before the dinosaurs

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

The ancient gradients were probably weaker than today’s, and whether they were continuous is argued (claim 19).

Later work looked for

Crossref, 2008 on, "latitudinal biodiversity gradient through deep time": Mannion and others (2014) find the gradient intermittent; page corrected and the review added.

Corrected

24 September 2026. Previously: “The gradient is older than the dinosaurs.” Stated as a continuous gradient. A later review of the fossil record finds the tropical peak absent for long greenhouse intervals.

Claim 18 · checked 24 September 2026 · AI-assisted audit

Claim: though perhaps not continuously: a 2014 review of the fossil record finds a tropical peak only in parts of the Palaeozoic and in the past 30 million years, with flatter gradients or temperate peaks in warmer times.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

  • Supports

    The latitudinal biodiversity gradient through deep timeabstract

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record · Review of the field

    The source reads: a tropical peak and poleward decline in species diversity has not been a persistent pattern throughout the Phanerozoic, but is restricted to intervals of the Palaeozoic and the past 30 million years ... warmer greenhouse regimes display temperate diversity peaks or flattened gradients

What this does not establish

The review was read only as an abstract. The fossil record is unevenly sampled by latitude, which affects every reading of it.

Other readings

The 2007 review reads the same record as a gradient with roots through the Mesozoic and into the Palaeozoic, weaker than today’s.

Corrected

24 September 2026. Previously: “” Added to report the rival reading of the fossil record (see claim 18).

Claim 19 · checked 24 September 2026 · AI-assisted audit

Claim: Exceptions exist

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Source checked. The cited passage was read, and it says this.

Later work looked for

Crossref, 2005 on, "latitudinal diversity gradient meta-analysis": nothing that removes the exceptions.

Claim 20 · checked 24 September 2026 · AI-assisted audit

Claim: and they are informative.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s own judgement, carried by what follows: the marine exception bears on temperature and on sampling (claims 22 to 25).

Claim 21 · checked 24 September 2026 · AI-assisted audit

Claim: In the sea the gradient often looks bimodal, with a dip in richness at the equator and peaks to either side whose positions vary by group.

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

  • Supports

    Bimodality of latitudinal gradients in marine species richnessabstract

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Research in animals · Observational study: associations, not causes

    The source reads: we found that almost all datasets were significantly bimodal with a dip in species richness near the equator. The locations of mid-latitude peaks varied between taxa

What this does not establish

The survey was read only as an abstract. Whether the dip is real or a sampling gap is argued (claim 23).

Later work looked for

Crossref, 2005 on, "latitudinal diversity gradient meta-analysis species richness": Menegotto and Rangel (2018) argue the dip is largely a sampling artefact; page corrected to report both.

Corrected

24 September 2026. Previously: “In the sea the gradient is often bimodal” A rival analysis attributes most of the dip to sparse tropical sampling.

Claim 22 · checked 24 September 2026 · AI-assisted audit

Claim: How much of the dip is real is argued: a 2018 analysis traces most of it to how thinly tropical waters have been sampled.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Mapping knowledge gaps in marine diversity reveals a latitudinal gradient of missing species richnessabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Observational study: associations, not causes

    The source reads: The tropical gap in species distribution seems a consequence of reduced sampling effort at low latitudes. Overall, our results suggest that spatial gaps in species distribution are the main cause of the bimodal pattern of marine diversity

  • Supports

    Mapping knowledge gaps in marine diversity reveals a latitudinal gradient of missing species richnessIntroduction, last paragraph

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Observational study: associations, not causes

    The source reads: We concluded that a bimodal pattern in marine species richness arise because of a tropical gap in species distribution, which is strongly associated with low sampling effort in the tropics.

    Occurrence records of about 35,000 marine species, in 5° latitude bands.

  • Qualifies

    Mapping knowledge gaps in marine diversity reveals a latitudinal gradient of missing species richnessabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals

    The source reads: only increasing sampling effort at low latitudes will reveal if the absence of species in the tropics, and the consequent dip in species richness, are artefacts of sampling bias or a natural phenomenon

What this does not establish

An analysis of occurrence records, not a new survey. Its authors say the question will be settled only by more sampling at low latitudes, and not every group is bimodal: copepods, stony corals and tunas have a single peak.

Other readings

The 2016 survey reads the dip as real and tied to temperature; the plankton record (claim 24) shows a dip in a well-preserved group.

Corrected

24 September 2026. Previously: “” Added: the bimodal gradient is contested, and the page reported one side.

Claim 23 · checked 24 September 2026 · AI-assisted audit

Claim: Fossil plankton, which preserve exceptionally well, show the dip opening as the ocean warmed after the last ice age

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

  • Supports

    Past and future decline of tropical pelagic biodiversityabstract and Significance

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record · Observational study: associations, not causes

    The source reads: a unimodal (or only weakly bimodal) diversity gradient, with a plateau in the tropics, occurred during the last ice age and has since then developed into a bimodal gradient through species distribution shifts driven by postglacial ocean warming

  • Supports

    Past and future decline of tropical pelagic biodiversitySignificance

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record

    The source reads: the calcified shells of planktonic foraminifers, abundant unicellular organisms in the world's oceans, which are exceptionally well preserved in marine sediments as fossils

What this does not establish

One group, planktonic foraminifera. Read only as an abstract and Significance statement.

Later work looked for

Crossref, 2017 on, "marine latitudinal diversity gradient bimodal equator": nothing found that revises the plankton result.

Corrected

24 September 2026. Previously: “Fossil plankton show that dip opening as the ocean warmed after the last ice age, which suggests the equator may already be too hot for some of what lives there.” The "too hot" inference is the 2016 survey’s, not the plankton study’s, and is now attributed to it.

Claim 24 · checked 24 September 2026 · AI-assisted audit

Claim: and the survey that described the bimodality suggests the equator may already be too hot for some species.

Kind
Hypothesis. A proposed explanation, not an established one.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

What this does not establish

A suggestion from a pattern, not a measured limit. Read only as an abstract.

Claim 25 · checked 24 September 2026 · AI-assisted audit

Three kinds of explanation

Claim: Three kinds of explanation

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Claim 26 · checked 24 September 2026 · AI-assisted audit

Claim: A 2007 review sorted the proposals into three kinds: ecological limits on how many species a place can hold, differences in the rate at which lineages diversify, and differences in how long the tropics have been there to diversify in.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Evolution and the latitudinal diversity gradient: speciation, extinction and biogeographyp. 316, Introduction

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: ecological hypotheses that focus on mechanisms of species coexistence and the maintenance of species diversity (Fig. 1a), evolutionary hypotheses that focus on rates of diversification (Fig. 1b), and historical hypotheses that focus on the duration and extent of tropical environments

Claim 27 · checked 24 September 2026 · AI-assisted audit

Claim: Counted region by region, movement between regions is a fourth term

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Claim 28 · checked 24 September 2026 · AI-assisted audit

Claim: and leaving it out is how the same data has been read two ways.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s reading of the review: older polar genera look like evidence about local extinction until movement from the tropics is counted, which is how the cradle and museum readings could both be drawn.

Claim 29 · checked 24 September 2026 · AI-assisted audit

Claim: The review found accumulating evidence for higher diversification in the tropics, from phylogenies and from fossils, and attributed it in part to faster tropical speciation.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Evolution and the latitudinal diversity gradient: speciation, extinction and biogeographyp. 326, Conclusions

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: There is also accumulating evidence for higher rates of diversification in the tropics compared with the temperate zone in many taxa, and this appears to be due, in part, to greater tropical speciation. This evidence is based on both palaeontological and phylogenetic studies

What this does not establish

What the review found in 2007. Later phylogenies disagree by group (claim 38).

Claim 30 · checked 24 September 2026 · AI-assisted audit

Claim: How extinction rates vary with latitude, it said, was little known.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Corrected

24 September 2026. Previously: “Latitudinal differences in extinction rate were what it knew least about.” The review says little is known; it does not rank this as the least known.

Claim 31 · checked 24 September 2026 · AI-assisted audit

Claim: It also counted the greater age and former extent of tropical environments as part of the answer, an idea that had had far less attention than ecological ones.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

The review also says the longer duration does not by itself explain the gradient.

Corrected

24 September 2026. Previously: “And tropical environments having been older and more widespread for much of Earth’s history is a real contributor that is often left out.” Attributed to the review, and "often left out" narrowed to what it says: such hypotheses had received far less attention than ecological ones.

Claim 32 · checked 24 September 2026 · AI-assisted audit

Claim: Where the difference would have to come from

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: More are made

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: Higher temperatures were proposed to raise evolutionary speed

Kind
Hypothesis. A proposed explanation, not an established one.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

The review lists it as a hypothesis and notes it applies only to cold-blooded organisms, while warm-blooded ones show the gradient too.

Corrected

24 September 2026. Previously: “Higher temperatures raise evolutionary speed” A hypothesis was stated as fact.

Claim 35 · checked 24 September 2026 · AI-assisted audit

Claim: and early evidence pointed to faster molecular evolution in some tropical taxa

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Corrected

24 September 2026. Previously: “and molecular evolution does run faster in some tropical taxa” The review calls this early evidence; the page stated it as settled.

Claim 36 · checked 24 September 2026 · AI-assisted audit

Claim: Narrower physiological tolerances and a larger tropical area were proposed to give more opportunity for populations to be isolated

Kind
Hypothesis. A proposed explanation, not an established one.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

The review says the data to test the physiological version, nearly forty years old in 2007, did not exist.

Corrected

24 September 2026. Previously: “Narrower physiological tolerances and a larger tropical area give more opportunity for populations to be isolated” Two hypotheses were stated as fact.

Claim 37 · checked 24 September 2026 · AI-assisted audit

Claim: Phylogenies disagree: mammals form new species faster in the tropics, marine fishes fastest outside them

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

What this does not establish

Rates are inferred from time-calibrated trees of living species, not observed. The fish study was read only as an abstract.

Other readings

A 2017 review reads the recent rates as often highest where richness is low, and as shaped by the gradient as much as shaping it.

Later work looked for

Crossref, 2010 on, "latitudinal gradient extinction rate tropics", found Rolland and others (2014); the fish study (2018) and the 2017 review were then read by DOI. Page corrected.

Corrected

24 September 2026. Previously: “Phylogenies support faster tropical diversification” Later phylogenies split by group: faster tropical speciation in mammals, faster high-latitude speciation in marine fishes.

Claim 38 · checked 24 September 2026 · AI-assisted audit

Claim: and a link from faster molecules to faster speciation had not been shown by 2007

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Corrected

24 September 2026. Previously: “but nobody has shown the link from faster molecules to faster speciation” The source is a 2007 review; "nobody has shown" stated it as current. Dated to the review.

Claim 39 · checked 24 September 2026 · AI-assisted audit

Claim: Fewer are lost, and there has been longer

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: Stable tropical climates were proposed to reduce the chance of extinction, by Darwin and by Wallace among others

Kind
Historical claim. A statement about the past that historical evidence can test.
Review
Source checked. The cited passage was read, and it says this.

Claim 41 · checked 24 September 2026 · AI-assisted audit

Claim: Pleistocene glacial cycles fell disproportionately on lineages living at high latitudes

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Claim 42 · checked 24 September 2026 · AI-assisted audit

Claim: Tropical conditions have covered more of the planet for more of its history

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Claim 43 · checked 24 September 2026 · AI-assisted audit

Claim: and how extinction varies with latitude is notoriously hard to estimate

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Corrected

24 September 2026. Previously: “and how extinction rate varies with latitude is the least known part of the problem” The review does not rank it as the least known; it says estimates are scarce and hard to make.

Claim 44 · checked 24 September 2026 · AI-assisted audit

Reading it out of the fossils

Claim: Reading it out of the fossils

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: A 2006 study took the question to the marine fossil record, tracking genera and subgenera of bivalves through the past 11 million years and counting origination, extinction and immigration separately.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

  • Supports

    Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradientabstract

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record · Observational study: associations, not causes

    The source reads: Using a spatially explicit approach that incorporates not only origination and extinction but immigration, a global analysis of genera and subgenera of marine bivalves over the past 11 million years

What this does not establish

The study was read only as an abstract.

Claim 46 · checked 24 September 2026 · AI-assisted audit

Claim: It found that taxa preferentially originate in the tropics and expand towards the poles without losing their tropical presence, a pattern the authors called out of the tropics.

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

  • Supports

    Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradientabstract

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record · Observational study: associations, not causes

    The source reads: supports an “out of the tropics” model, in which taxa preferentially originate in the tropics and expand toward the poles without losing their tropical presence

What this does not establish

Marine bivalve genera and subgenera, over 11 million years. The study was read only as an abstract.

Later work looked for

Crossref, 2007 on, "out of the tropics bivalves latitudinal diversity gradient": the authors’ 2013 PNAS follow-up and Rolland and others (2014), who find out-of-the-tropics range expansion in mammals; nothing that reverses it.

Claim 47 · checked 24 September 2026 · AI-assisted audit

Claim: That makes the tropics a cradle and a museum at once, against a dichotomy that had stood since 1974.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

What this does not establish

The authors’ conclusion, read only in the abstract. The 1974 dichotomy is Stebbins’s cradle or museum question, named in the 2007 review.

Claim 48 · checked 24 September 2026 · AI-assisted audit

Claim: A study of one genus of tropical American leaf beetles reached the same answer the same year

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

  • Supports

    Tropical forests are both evolutionary cradles and museums of leaf beetle diversityabstract

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Research in animals · Model

    The source reads: approved May 26, 2006 ... From an extensively sampled molecular phylogeny of herbivorous Neotropical leaf beetles in the genus Cephaloleia ... These results demonstrate that, for Cephaloleia and perhaps other lineages of organisms, tropical forests are at the same time both evolutionary cradles and museums of diversity.

What this does not establish

One Neotropical genus, from a molecular phylogeny. Read only as an abstract.

Corrected

24 September 2026. Previously: “Leaf beetles gave the same answer the same year” The study covers one genus, Cephaloleia, not leaf beetles in general. The study is now cited.

Claim 49 · checked 24 September 2026 · AI-assisted audit

Claim: and the 2007 review took the pair as where the evidence stood.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Evolution and the latitudinal diversity gradient: speciation, extinction and biogeographyp. 326, Conclusions

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: Current evidence points to the tropics as both a museum and a cradle (sensu Stebbins 1974); taxa not only preferentially originate in the tropics but tend to also persist there longer (Jablonski et al. 2006; McKenna & Farrell 2006).

Corrected

24 September 2026. Previously: “and the 2007 review took the pair as where the evidence now stands.” A 2007 judgement was written in the present tense.

Claim 50 · checked 24 September 2026 · AI-assisted audit

The explanations

Claim: The explanations

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: Speciation, extinction, time, and what moves in from somewhere else.

Kind
Framing. Signposting. It asserts nothing a source could check.

Why the answer matters practically

Claim: Why the answer matters practically

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: If tropical richness reflects a slow accumulation over tens of millions of years, it cannot be rebuilt on any human timescale once lost.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s own inference from the time and area account, where diversity accumulates over geological time.

Claim 54 · checked 24 September 2026 · AI-assisted audit

Claim: If it reflects faster speciation, the loss is no less severe, because even fast speciation runs on a geological clock.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s own inference. It follows from the review’s note that most speciation takes far longer than ten thousand years.

Corrected

24 September 2026. Previously: “If it reflects ongoing rapid speciation, the loss is still severe and the recovery is at least conceivable.” Recovery being "conceivable" implied a human timescale that no source supports; faster tropical speciation is still far slower than that.

Claim 55 · checked 24 September 2026 · AI-assisted audit

Claim: The two stories still differ in what conservation is protecting: an archive in one, a source of new species in the other.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s own reading of the museum and cradle accounts (claims 48 and 50), put in conservation terms.

Corrected

24 September 2026. Previously: “The two stories have very different implications for what conservation is protecting.” Rewritten to follow from the corrected sentence before it, and to say what the difference is.

Claim 56 · checked 24 September 2026 · AI-assisted audit

Claim: The bivalve study put it flatly: a tropical diversity crisis would have evolutionary effects at every latitude.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

What this does not establish

The authors’ inference from marine bivalves, read in the abstract.

Claim 57 · checked 24 September 2026 · AI-assisted audit

Whether one explanation is required

Claim: Whether one explanation is required

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: Different groups may reach the same pattern by different routes

Kind
Hypothesis. A proposed explanation, not an established one.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

Shown within mammals, from rates inferred on a phylogeny. That it holds across the tree of life is the proposal, not a finding.

Claim 59 · checked 24 September 2026 · AI-assisted audit

Claim: in which case looking for a single cause is a mistake in the framing of the question rather than a failure to find the answer.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s conditional reading. The 2019 review calls the hypotheses non-mutually exclusive.

Claim 60 · checked 24 September 2026 · AI-assisted audit

Claim: A 2019 review says plainly that no consensus has been reached and that the observed patterns are often consistent with several explanations at once.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Corrected

24 September 2026. Previously: “Reviews now say plainly” The claim rests on one review, published in 2019.

Claim 61 · checked 24 September 2026 · AI-assisted audit

Claim: That is less satisfying and better supported.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s judgement, following from claims 59 and 61: several explanations at once fit the evidence better than any one of them.

Claim 62 · checked 24 September 2026 · AI-assisted audit

What was read