Hello. I hope my answer isn't getting to you too late. I haven't worked with this particular equation, but from other experiences with ecology statistics, I think I can give you a general response on how to use it.

Going by your book, we have:

HPI = Habitat Preference Index

Px = percentage of the population in the x habitat

Pa = percentage of the x habitat relative to the total study area

Let's try to apply it to an example with random numbers. We'll say we have a deer population of 50 individuals that inhabits an area of 10km2. Then, we'll say around 40% of this area is characterized by a "wetland" type habitat, the rest being grassland. Your question then is: "¿What percentage of this population prefers the wetland over the grassland?"

(Obviously we're leaving aside factors like the time of stay or migration from or to each area, but this is for simplicity's sake of the example)

Let's say then, that you've registered 30 of those deer individuals that choose to live in the wetland habitat rather than the grassland. That means that of your total of 50, 60% of your population prefers wetland. With this, we can replace the numbers on your equation:

Px = 60% Pa = 40%

HPI = 60% / 40% = 1.5

Your HPI would be 1.5 in this case. Your book should have a table or similar reference for you to compare this result with the general index and interpret your particular study with it.

I hope this was of help, if you believe I've made a mistake anywhere, please do tell me. Good luck on yout research.

Thank you for the analogical answer, Maria. i've been changing my equation for my method. now, i used to Neu Index. bcs i can't find any source about HPI from another literature... maybe, do you know something about the Neu Index? if u know, reply me pls.. thx