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D. S. de Ron et al. 2010. Habitat suitability models for two species of forest raptors in Catalonia
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Equation 1 shows that final model includes only land uses variables, not topographic or climatic
ones. Two single variables (A, F) and three interactions between A, F y C slightly explain actual
distribution of common buzzard in the study area (Table 3). There is no evident explanation to
the incidence of interaction variables, whereas the positive effect of forest areas is obvious but
the same effect of artificial in not so much explainable.
4. Discussion
The paper explores the use of recently sampled data of nesting birds in Catalonia in relation
with main land uses and other topographic and climatic variables. Presence/absence data at 1 x 1
km 2 resolution and frequency data at 10 x 10 km 2 where used for modeling Habitat Suitability
for two forest raptors species. Surprisingly, no relationships where found at the more detailed
scale, and only a slight relation could be modeled (Figure 2) for the more abundant raptor
species (common buzzard) at a coarser resolution level.
These are not good news because high spatial resolution data of species distribution should be
the basis for modeling connectivity, habitat fragmentation and other indicators relatives to
species conservation. If we could not model in relation with the main territorial requirements of
a species, and where they are located across the territory, it would be difficult to predict species
colonization movements or habitat loss driving forces.
It should be possible that the two main reasons that affect the absence of correlation found at 1 x
1 km 2 resolution, is that the sampled territory is less than 10 % of total territory and land uses
distribution in species presence plots and total plots is quite similar, where no determinant for
other species and other sampling areas at the same resolution levels, but there are not very much
reasons to be optimist with the problem of true or false absences. Manel et al (2001) showed
some problems that are not been solved in data acquisition methods, and modeling HSM with
this kind of data is not so accurate.
Next question is relative to habitat saturation by a target species in a territory. This relationship
depends not only of potential habitat or potential niche but also of the effective niche. There are
some biotic interdependence that land uses variables or climatic and topographic ones do not
reflect. Human pressure in Spain over raptor species had historically reduced their distribution
areas, driving some of them near extinction. Absence of preys is other meaningful reason that
we could not evaluate in these models, and for the migrant species maybe questions relative to
synchronization of movements are important too.
Finally, we could conclude that the use of presence/absence data at 1 x 1 km 2 resolution for
two raptors species in Cataluña, in relation with land use, climatic and tophographic variables
had not improved the slight predictive power of the HSM at 10 x 10 km 2 resolution. Including
variables of avian richness, potential prey’s richness or some relative could be improving the
response of models but, in general, data relative to these variables are not available at broad
scales.
References
Alderman, J., McCollin, D., Hinsley, S. A., Bellamy, P. E., Picton, P. & Crockett, R. 2005.
Modelling the effects of dispersal and landscape configuration on population distribution
and viability in fragmented habitat. Landscape Ecology. 20: 857-870
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.