Add feature weights
Conservation planning problems that aim to maximize the representation of features given a budget often will not able to conserve all of the features unless the budget is very high. In such budget-limited problems, it may be desirable to prefer the representation of some features over other features. This information can be incorporated into the problem using weights. Weights can be applied to a problem to favor the representation of some features over other features when making decisions about how the budget should be allocated.
## S4 method for signature 'ConservationProblem,numeric' add_feature_weights(x, weights) ## S4 method for signature 'ConservationProblem,matrix' add_feature_weights(x, weights)
x |
|
weights |
|
Weights can only be applied to problems that have an objective
that is budget limited (e.g. add_max_cover_objective()
).
They can be applied to problems that aim to maximize phylogenetic
representation (add_max_phylo_div_objective()
) to favor the
representation of specific features over the representation of
some phylogenetic branches. Weights cannot be negative values
and must have values that are equal to or larger than zero.
Note that planning unit costs are scaled to 0.01 to identify
the cheapest solution among multiple optimal solutions. This means
that the optimization process will favor cheaper solutions over solutions
that meet feature targets (or occurrences) when feature weights are
lower than 0.01.
Object (i.e. ConservationProblem
) with the weights
added to it.
The argument to weights
can be specified using the following formats.
numeric
containing weights for each feature. Note that this type of argument cannot be used to specify weights for problems with multiple zones.
matrix
containing weights for each feature in each zone.
Here, each row corresponds to a different feature in argument to
x
, each column corresponds to a different zone in argument to
x
, and each cell contains the weight value for a given feature
that the solution can to secure in a given zone. Note that
if the problem contains targets created using
add_manual_targets()
then a matrix
should be
supplied containing a single column that indicates that weight for
fulfilling each target.
# load ape package require(ape) # load data data(sim_pu_raster, sim_features, sim_phylogeny, sim_pu_zones_stack, sim_features_zones) # create minimal problem that aims to maximize the number of features # adequately conserved given a total budget of 3800. Here, each feature # needs 20% of its habitat for it to be considered adequately conserved p1 <- problem(sim_pu_raster, sim_features) %>% add_max_features_objective(budget = 3800) %>% add_relative_targets(0.2) %>% add_binary_decisions() %>% add_default_solver(verbose = FALSE) # create weights that assign higher importance to features with less # suitable habitat in the study area (w2 <- exp((1 / cellStats(sim_features, "sum")) * 200)) # create problem using rarity weights p2 <- p1 %>% add_feature_weights(w2) # create manually specified weights that assign higher importance to # certain features. These weights could be based on a pre-calculated index # (e.g. an index measuring extinction risk where higher values # denote higher extinction risk) w3 <- c(0, 0, 0, 100, 200) p3 <- p1 %>% add_feature_weights(w3) ## Not run: # solve problems s1 <- stack(solve(p1), solve(p2), solve(p3)) # plot solutions plot(s1, main = c("equal weights", "rarity weights", "manual weights"), axes = FALSE, box = FALSE) ## End(Not run) # plot the example phylogeny ## Not run: par(mfrow = c(1, 1)) plot(sim_phylogeny, main = "simulated phylogeny") ## End(Not run) # create problem with a maximum phylogenetic diversity objective, # where each feature needs 10% of its distribution to be secured for # it to be adequately conserved and a total budget of 1900 p4 <- problem(sim_pu_raster, sim_features) %>% add_max_phylo_div_objective(1900, sim_phylogeny) %>% add_relative_targets(0.1) %>% add_binary_decisions() %>% add_default_solver(verbose = FALSE) ## Not run: # solve problem s4 <- solve(p4) # plot solution plot(s4, main = "solution", axes = FALSE, box = FALSE) # find out which features have their targets met r4 <- eval_target_coverage_summary(p4, s4) print(r4, width = Inf) # plot the example phylogeny and color the represented features in red plot(sim_phylogeny, main = "represented features", tip.color = replace(rep("black", nlayers(sim_features)), which(r4$met), "red")) ## End(Not run) # we can see here that the third feature ("layer.3", i.e. # sim_features[[3]]) is not represented in the solution. Let us pretend # that it is absolutely critical this feature is adequately conserved # in the solution. For example, this feature could represent a species # that plays important role in the ecosystem, or a species that is # important commercial activities (e.g. eco-tourism). So, to generate # a solution that conserves the third feature whilst also aiming to # maximize phylogenetic diversity, we will create a set of weights that # assign a particularly high weighting to the third feature w5 <- c(0, 0, 1000, 0, 0) # we can see that this weighting (i.e. w5[3]) has a much higher value than # the branch lengths in the phylogeny so solutions that represent this # feature be much closer to optimality print(sim_phylogeny$edge.length) ## Not run: # create problem with high weighting for the third feature and solve it s5 <- p4 %>% add_feature_weights(w5) %>% solve() # plot solution plot(s5, main = "solution", axes = FALSE, box = FALSE) # find which features have their targets met r5 <- eval_target_coverage_summary(p4, s5) print(r5, width = Inf) # plot the example phylogeny and color the represented features in red # here we can see that this solution only adequately conserves the # third feature. This means that, given the budget, we are faced with the # trade-off of conserving either the third feature, or a phylogenetically # diverse set of three different features. plot(sim_phylogeny, main = "represented features", tip.color = replace(rep("black", nlayers(sim_features)), which(r5$met), "red")) ## End(Not run) # create multi-zone problem with maximum features objective, # with 10% representation targets for each feature, and set # a budget such that the total maximum expenditure in all zones # cannot exceed 3000 p6 <- problem(sim_pu_zones_stack, sim_features_zones) %>% add_max_features_objective(3000) %>% add_relative_targets(matrix(0.1, ncol = 3, nrow = 5)) %>% add_binary_decisions() %>% add_default_solver(verbose = FALSE) # create weights that assign equal weighting for the representation # of each feature in each zone except that it does not matter if # feature 1 is represented in zone 1 and it really important # that feature 3 is really in zone 1 w7 <- matrix(1, ncol = 3, nrow = 5) w7[1, 1] <- 0 w7[3, 1] <- 100 # create problem with weights p7 <- p6 %>% add_feature_weights(w7) ## Not run: # solve problems s6 <- solve(p6) s7 <- solve(p7) # plot solutions plot(stack(category_layer(s6), category_layer(s7)), main = c("equal weights", "manual weights"), axes = FALSE, box = FALSE) ## End(Not run) # create minimal problem to show the correct method for setting # weights for problems with manual targets p8 <- problem(sim_pu_raster, sim_features) %>% add_max_features_objective(budget = 3000) %>% add_manual_targets(data.frame(feature = c("layer.1", "layer.4"), type = "relative", target = 0.1)) %>% add_feature_weights(matrix(c(1, 200), ncol = 1)) %>% add_binary_decisions() %>% add_default_solver(verbose = FALSE) ## Not run: # solve problem s8 <- solve(p8) # plot solution plot(s8, main = "solution", axes = FALSE, box = FALSE) ## End(Not run)
Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.