The effects of President Trump’s immigration crackdown can be seen at deserted Mexican border shelters, in the plummeting numbers of illegal crossings and at workplaces raided by federal agents.

But to get a glimpse of the alarm jolting Latin American immigrant communities in the United States, migrants, rights workers and experts say, follow the money.

“There is fear,” said Julio Fuentes, a 35-year-old undocumented migrant from Guatemala who works in California as a plumber. “Because if they catch you, then you can’t do anything. And they send you home with nothing.”

Over the last several months, the amount of money sent by migrants like Mr. Fuentes back to their native countries in Latin America has jumped by billions of dollars in total, according to financial institutions in the region. Migrants typically send a few hundred or a few thousand dollars at a time through cash at transfer shops or through digital methods.

Across several Central American nations money transfers have jumped 20 percent.

The reason, officials, migrants and analysts say, is that people afraid of being deported are trying to get as much money out of the country as possible, while they still can.

The money transfers, called remittances, are a critical lifeline for many countries and families around the world, especially in Central America and the Caribbean. There, the funds sometimes make up a huge chunk of a nation’s economy — as much as a quarter of a country’s gross domestic product, as in Honduras and Nicaragua.