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From species detection to population size indexing: the use of sign surveys for monitoring a rare and otherwise elusive small mammal
Publication . Peralta, Dinora; Vaz‑Freire, Teresa; Ferreira, Clara; Mendes, Tiago; Mira, António; Santos, Sara; Alves, Paulo C.; Lambin, Xavier; Beja, Pedro; Paupério, Joana; Pita, Ricardo
Monitoring the occupancy and abundance of wildlife populations is key to evaluate their conservation status and trends.
However, estimating these parameters often involves time and resource-intensive techniques, which are logistically challeng-
ing or even unfeasible for rare and elusive species that occur patchily and in small numbers. Hence, surveys based on field
identification of signs (e.g. faeces, footprints) have long been considered a cost-effective alternative in wildlife monitoring,
provided they produce reliable detectability and meaningful indices of population abundance. We tested the use of sign sur-
veys for monitoring rare and otherwise elusive small mammals, focusing on the Cabrera vole (Microtus cabrerae) in Portugal.
We asked how sampling intensity affects true positive detection of the species, and whether sign abundance is related to
population size. We surveyed Cabrera voles’ latrines in 20 habitat patches known to be occupied, and estimated ‘true’ popula-
tion size at each patch using DNA-based capture-recapture techniques. We found that a searching rate of ca. 3 min/250m2 of
habitat based on adaptive guided transects was sufficient to provide true positive detection probabilities > 0.85. Sign-based
abundance indices were at best moderately correlated with estimates of ‘true’ population size, and even so only for search-
ing rates > 12 min/250m 2 . Our study suggests that surveys based on field identification of signs should provide a reliable
option to estimate occupancy of Cabrera voles, and possibly for other rare or elusive small mammals, but cautions should
be exercised when using this approach to infer population size. In case of practical constraints to the use of more accurate
methods, a considerable sampling intensity is needed to reliably index Cabrera voles’ abundance from sign surveys.
dispfit: An R package to estimate species dispersal kernels
Publication . Proença-Ferreira, António; Borda-de-Água, Luís; Porto, Miguel; Mira, António; Moreira, Francisco; Pita, Ricardo
Dispersal of organisms is a ubiquitous aspect of the natural world, with wide implications across scales and
organization levels. Interest in dispersal has risen sharply over the past 30 years, mostly due to the multiple and
rapid global changes ecosystems face. Among the various aspects that may characterize a dispersion event,
dispersal distance is considered a key descriptor in a wide variety of studies across taxonomic groups. Typically,
dispersal distances are defined in the form of dispersal kernels describing the dispersal distance distribution
according to probability density functions. Although numerous methods providing dispersal data exist, there is
still a lack of intuitive and comprehensive approaches and tools to estimate dispersal kernels from such data.
Here we present the dispfit package, an R software application developed to fill this gap. dispfit fits and compares
different families of parameterized functions to describe and predict dispersal distances. It includes 9 well-known
and commonly used distributions, computes goodness-of-fit and model selection statistics, and estimate each
distribution's parameters, along with their first four moments (mean, standard deviation, skewness, and kurtosis).
We describe the main functions included in dispfit and provide an example to illustrate the workflow of the
typical analyses performed within the package. We believe that dispfit will critically contribute to improving the
modelling of species' dispersal distances, thus enhancing the understanding of the ecological and evolutionary
processes involving dispersal movement.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
Projetos de Investigação Científica e Desenvolvimento Tecnológico - 2014 (P2020)
Número da atribuição
PTDC/BIA-BIC/6582/2014