I am working with plants aner in our experiments we include all age classes.

An opportunity for you could also be to build two classes (young & adult) per species. This gives you the opportunity to analyse it in multiple ways - i) all together, ii) only regarding adults respectively young and iii) to compare if including young individuals changes the "only adult" results.

But as said right in the beginning I am working with plants and I am not an animal expert

Yes, as you say, juvenile animals tend to have a much lower chance of survival compared to adults. Depending on your situation, it might be appropriate to: 1) just count all adults, 2) just count biologically relevant units (e.g., family groups, breeding pairs, breeding females, or breeding males), 3) count all individuals (adults + juveniles). But, if you choose the last option of counting adults and juveniles, you should account for lower survival rates of juveniles. Ways to do this would be to just report juvenile numbers separately from adult numbers. Or else, as you described, you could give juveniles a score less than 1 (1 being adult survival). So to use your example, count a juvenile as 0.25 if it has a 1/4 chance of survival compared to an adult. If you do not have information on juvenile survival, you could use estimates of juvenile survival of a different similar species.

Actually, although I don't know anything about your system and situation, if I were you I would probably only use counts of adults to estimate abundance. And then maybe just report juvenile numbers separately somewhere in the results of the report.

Good luck!

I would avoid indices of abundance. They require the same assumptions as population estimates or occupancy estimates, but also assume a linear (or some other predictable) relationship between the index and actual abundance. If you do stick with your index, please validate it to ensure that this linear relationship actually exists.

Nowadays there are really robust methods of estimating population size that negate the need to use indices. Things like Marcus Rowcliffe's entropy model (Rowcliffe, J.M., Field, J., Turvey, S.T. & Carbone, C. (2008) Estimating animal density using camera traps without the need for individual recognition. Journal of Applied Ecology, 45, 1228-1236.) or occupancy modelling (MacKenzie, D.I., Nichols, J.D., Royle, J.A., Pollock, K.H. & Bailey, L.L. (2006) Occupancy Estimation and Modelling: Inferring Patterns and Dynamics of Species Occurrence. Elsevier, London, U.K.).

I have just recommended the previous answers, although they are not completely homogeneous. I am not a teriologist or a botanist, but essentially an entomologist. The biological model I use are the Scarabeid Beetles, holometabolous Insects, so the numbers I analyze refer only to adults. The problem is however very interesting - and important - in theoretical terms, and raises many doubts. A similar doubt, in the biogeographical field, is how to consider, as part of the population of a given area, the sedentary species. migratory ones. I will follow the debate with the utmost attention

Are you reporting the population as it was when you surveyed it, or predicting what it will be at some time in the future ?. If the first then you can ignore the likely future mortality of juveniles (which applies also to very old adults), but you should report juveniles and adults separately (and, I would suggest, males and females separately if you can discriminate them in your videos). If you need to forecast a future population then you will need values for parameters such as age-specific mortality, and you will not get those from a camera trapping survey.

Hi,

I agreed with the before comments. About your question i think your decision should be taken based on your main aim. If your goal is to understand some demographic pattern you should count separately youngs and adult animals, but i dont think is a good idea to arbitri decide the survive rate for of the age classes.

For the other hand, if you want to compare only abundance of species as a response variable, your counts must be based on independents register, becouse if you count a young animal like 0.25 probably you would get sub or overestimation of the N (estimate number of animals). Further , i recomend no to use relative abundance (RAI) because they do not take the imperfect of detection. You can get good result with other model like N-mixture models for count-data, Distance models and occupancy models (Royle-Nichols) for presence-absence data, so i encourage to use one of them.

I give you some papers related to your aim with Peccaries and tapirs mey be it can clariffied your doub.

Article Abundance variation of ungulates in two protected areas of t...

Article Density, relative abundance or occupancy of the collared pec...

regards, G

I agree with a previous responder on collecting data for all age classes, though I also research plants rather than animals. Best to collect the data and categorise and determine usefulness or otherwise later. Depending on your research aim, it may later emerge that numbers of different age classes may be indicators of species population health or of seasonal and environmental factors occurring.

The use of relative abundance indices has been actively discouraged in the literature over the last few years. The reason is that there is no clear relationship between true abundance and detections, especially on camera traps (Ie. You are not factoring in detection probability into this approach). One of the clearest and most striking field examples of this was some of Phil Henschels work on Leopards in Gabon - He almost never detected Sitatunga on roads and in primary forest, but they were in the landscape, just in the marshes where one would expect! As Matt says in some of the papers he listed the methods are now well understood and estimating densities is easy and robust!

Hello,

There is no right answer to your question. Perhaps its not even the right question. Imagine a life table from birth to old age. Now think in terms of comparing life tables rather than total abundance. Take the number of adult females as your index, then score the number of each other age-sex class as a multiple (infants = 2X AdF; yearlings = 1.8X AdF; AdM = 0.7 AdF. etc. This will give you a basis for assessing potential mortality rates and population growth rates as a basis for comparing between time periods or populations. This enables you to see each population as dynamic rather than static. Best of luck.

My two (or three) cents.

Preferable to estimate abundance directly, as Matt recommended, but occupancy itself is an index, so not suitable if estimating absolute abundance is a priority.

There are many situations when indices are the only viable choice and when they make more sense because they are easier/cheaper to collect. Occupancy is a prime example of this, and explains why so many resource agencies have adopted it.

The reason juveniles/subadults are generally not counted in carnivore surveys is because the primary methods we have for doing so (camera traps, track surveys) are generally biased, but if you can count them that is great! As others have indicated however, these indices should be presented separately if possible, and approach across sampling periods/sites should be standardised.