Reddit reviews The Emperor's Beard: Dom Pedro II and His Tropical Monarchy in Brazil

Hey, it's no problem - the numbers do tend to vary. Let's look over the losses listed in the texts I have on hand, because I don't trust Wikipedia and refuse to click on your link:

In Independence or Death!, the author says that Paraguay suffered an almost 50% casualty rate, leaving a population of 221,000, with only 28,000 of them men (12.6%) (p 198). However, all the way back on page 7, he says that the estimated population of Paraguay in 1864 ranged between 450,000 and 1.5 million, "with the former being more correct." If this is the case, then his postwar population estimate would be based on the absolute lowest estimate available, so take it with a grain of salt.

Paraguay: Power Game, a slim monograph, agrees with this number on page 20, but I don't consider it to be a trustworthy source since it is highly revisionist and clearly written to emphasize Paraguayan victimhood at the hands of foreign powers: it promotes the idea that the real cause of the war was that Brazil, Argentina, and the United Kingdom wanted access to Paraguay's natural resources, and that the UK was threatened because Paraguay was "creating a more autonomous economic model," as Lilia Schwarcz puts it in The Emperor's Beard (she doubts this theory). This is obvious BS given the fact that, on the very same page as that claim, the authors say that Lopez was the one who invaded Argentina and Brazil).

Fear and Memory in the Brazilian Army and Society has a short segment on the war, and although it gives no absolute numbers it says that 60%-69% of the Paraguayan population died, and that there was a gender imbalance of 1-4/5 men to women following the war.

In this biography of marshal Lopez, the population is first said to have been halved, but in the same paragraph it is also said to have been reduced by three quarters, with a 1-2 male-female imbalance. The total postwar population is said to be 116,000, although "[o]thers think the number [is] somewhat larger." (p 193)

He cites this paper, but the paper itself estimates the population to be between 141,351 and 166,351; he appears to have deliberately left out the authors' correction for regions which didn't participate in the 1870 census, and the gender imbalance is said to be 4/5 to 1. I don't trust this book much, since the author seems to personally hate Lopez - every single page drips with vitriol. Biographies of Hitler are less biased. Also, this paper casts doubt on their claims.

Based on all this I think we can kinda-sorta guesstimate that around half to three fifths of Paraguayans died, with four out of five men dying, but that a there is a lot of hedge betting going on. There are other papers on this subject and I've avoided Spanish and Portuguese texts because my Portuguese is very bad and I don't speak Spanish at all, so there are some limitations. Also, I'd be happy to share the papers with you if you don't have access to JSTOR yourself, but I think I'll take a break. If I've messed up in some monumental way, please report me to /r/badhistory. :)