We are, at the same time, witnesses and drivers of the loss of biodiversity throughout the planet. We are experiencing a general reduction in the abundance of many populations that may lead to their disappearance. If this process is repeated enough it can lead to the extinction of species.
Much of our understanding of these declines comes from comparing estimates that describe distributions and abundances of populations and species over time. However, the data necessary to calculate these estimates have only begun to be collected very recently, in the last few decades. By the time these data became available, the impacts of human activities on many species had been occurring for centuries.
In other words, our perception of recent declines may be a mere miniature of actual declines. Even the supposed expansion processes of some species may be no more than mirages, the result of looking at a very limited time window.
In an article just published in the journal Animal Conservation We show that this is the case for the wolf (canis lupus) in Spain.
Is the wolf expanding?
The distribution of the wolf in Spain reached its minimum expression around 1980. Since then, the species has recolonized some areas, although the estimated number of groups has remained practically unchanged in the two national censuses carried out (completed in 1988 and 2014).
These recent changes have sometimes been interpreted as a expansion of the wolf and various voices have claimed the need for its population control. The inclusion of the wolf in the List of Wild Species under a Special Protection Regime imposes strong limitations on these controls. This has encountered opposition among some social groups.
In this context, it is very important to have an objective evaluation of the long-term trend of wolf distribution in Spain, beyond what has happened in recent years. But, in the absence of historical data, where can information on the historical distribution of the wolf be obtained?
The answer lies outside the realm of the natural sciences.
There were wolves in 65% of peninsular Spain
The geographical dictionary edited by Pascual Madoz in the mid-nineteenth century was a titanic collective effort, with more than 1,400 participants, to describe each Spanish population center and geographic feature. Among the elements included in the descriptions are often species of wild animals, fundamentally those considered useful (hunted or fished) and harmful (wolves and other carnivores).
For the work on the wolf, we reviewed the more than 11,000 pages of the 16 volumes of the dictionary, compiling and locating on the map more than 1,500 mentions of the wolf, distributed throughout all the provinces of continental Spain.
This information is in itself very interesting, but the distribution of the wolf cannot be derived from it, as other works have done, since in many places in Spain the Madoz dictionary does not offer any information on fauna and in them the lack of mention of the wolf cannot be taken by its absence.
To solve this problem, more than 5,200 references to other species of terrestrial fauna were also collected and located. Thus, we consider as wolf absence zones those places in which animal species were mentioned but not the wolf.
The collection of localities with and without wolves extracted from the Madoz dictionary was used together with variables that described environmental and human population characteristics to estimate the distribution of the wolf in Spain in the mid-nineteenth century, through statistical models. The results showed that the presence of wolves was lower in the flatter areas, more suitable for agriculture and with a higher density of human population.
The analysis of these data allows us to estimate that the species occupied around 317,000 km², that is, up to 65% of the surface of peninsular Spain. It should be noted that this estimate of the occupied area should be taken as a minimum value. The fact that the presence of the wolf was not mentioned in a locality could be due to the fact that the species was not known in the area (true absence) or because the local informant did not consider this information important and did not provide it (false absence).
The wolf is a long way from recovery
Comparing the current situation with the historical distribution described through models, the area occupied today would mean just over 30% of the historical one. With this framework, the supposed recent expansion would imply little more than a stabilization of the sharp decline suffered by the species.
A true recovery of the species and its crucial ecological functions would imply its return to the areas of historical presence outside the northwestern quadrant of Spain, as contemplated by the recently approved Spanish strategy for the management and conservation of the wolf.
This horizon implies numerous challenges for the coexistence of humans and wolves, especially in places where the presence of the species is no longer part of the collective memory, but it also offers new possibilities in these areas.
The recently published work shows the potential of historical sources to understand the natural environment and inform its current management. Properly exploiting these sources implies a great effort and requires the application of appropriate statistical techniques to correct the gaps and biases contained in historical documents. But the effort is worth it if we manage to extend the time horizon in which we assess the state and trends of ecosystems and the species that occupy them.