Analyze This: Amphibian populations are on the decline | Science News for Students

Analyze This: Amphibian populations are on the decline

The chytrid fungus has been wiping out frogs around the world
May 29, 2019 — 6:30 am EST
an endangered mossy red-eyed frog (Duellmanohyla soralia) sitting on a green leaf

This is an endangered mossy red-eyed frog (Duellmanohyla soralia) from Honduras. Its species is among at least 500 whose numbers have declined due to chytrid fungal infections, a new tally shows. 

Jonathan E. Kolby/Honduras Amphibian Rescue & Conservation Center

A deadly disease has been traveling the world for more than three decades now. Called Batrachochytrium dendrobatidis, or Bd, it’s a fungal pathogen that infects the skin of frogs, toads and other amphibians. A related fungus, B. salamandrivorans, infects salamanders and newts. Together, these pathogens are known as chytrids (KIH-trids) because the disease they cause is called chytridiomycosis (Kih-TRIH-dee-oh-my-oh-KOH-sis).

Scientists have known that these pathogens can be deadly. They have documented the effects that chytrids have had on amphibian populations. Now researchers have tallied up the effects of one chytrid, Bd, on species around the world. Their report appeared March 29 in the journal Science.

Bd has played a role in the decline of some 500 amphibian species in the past 50 years, the scientists found. Australia and the Americas have been especially hard hit. But these declines have been occurred around the world, except in Asia. That’s where the fungus is thought to originate.

The pathogen may be responsible for the extinction of as many as 90 species, the researchers report. Others are still in peril. About 40 percent of those 500 species are still declining in numbers. And about one in every four of those species now hold on at less than a tenth of their former population size.

Amphibian declines due to chytrid fungus in Mesoamerica

a graph showing how chytrid fungal infections have impacted amphibian species in Mesoamerica
Central America, Mexico and the Caribbean Islands — a region known as Mesoamerica — has been hard hit by chytrid fungal infections. This chart divvies up species into how much their population numbers have declined due to the fungus.
Graph: B.C. Scheele et al/Science 2019, Frog: B. Gratwicke/Smithsonian Conservation Biology Institute 

Data Dive: 

1. What does each bar in the chart above represent?

2. According to the chart, how many species in Mesoamerica have gone extinct or are presumed extinct due to the chytrid fungus?

3. Can you determine from this chart if there are any species that have not been affected by the chytrid fungus? Explain your answer.

4. What is the overall message of this chart? What does it tell you about the effect of the chytrid fungi in Mesoamerica?

5. Critique the chart. How could you improve it? Is there another way that you could present this data?

Analyze This! explores science through data, graphs, visualizations and more. Have a comment or a suggestion for a future post? Send an email to

Power Words

(more about Power Words)

amphibians     A group of animals that includes frogs, salamanders and caecilians. Amphibians have backbones and can breathe through their skin. Unlike reptiles, birds and mammals, unborn or unhatched amphibians do not develop in a special protective sac called an amniotic sac.

chytrid fungus     A common shortened name for fungi — Batrachochytrium dendrobatidis and B. salamandrivorans —  that can create a lethal infection in amphibians, especially frogs. The formal name of the infection is chytridiomycosis.

extinct     An adjective that describes a species for which there are no living members.

extinction     The permanent loss of a species, family or larger group of organisms.

fungus     (plural: fungi) One of a group of single- or multiple-celled organisms that reproduce via spores and feed on living or decaying organic matter. Examples include mold, yeasts and mushrooms.

infect     To spread a disease from one organism to another. This usually involves introducing some sort of disease-causing germ to an individual.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

pathogen     An organism that causes disease.

population     (in biology) A group of individuals from the same species that lives in the same area.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

Further Reading


Journal:​ ​​ B.C. Scheele et al. Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversityScience. Vol. 363, March 29, 2019, p. 1459. doi: 10.1126/science.aav0379.