## Density as a Misleading Indicator of Habitat Quality > [!Cite]- > Horne, B. Van. “Density as a Misleading Indicator of Habitat Quality.” _The Journal of Wildlife Management_ 47, no. 4 (October 1983): 893. [https://doi.org/10.2307/3808148](https://doi.org/10.2307/3808148). > > [link](https://www.jstor.org/stable/3808148?origin=crossref) [online](http://zotero.org/users/local/kycSZ2wR/items/SI2RHTSE) [local](zotero://select/library/items/SI2RHTSE) [pdf](file://C:\Users\erikt\Zotero\storage\YE36RQJ4\Horne%20-%201983%20-%20Density%20as%20a%20Misleading%20Indicator%20of%20Habitat%20Quali.pdf) ## Notes %% begin notes %% %% end notes %% %% begin annotations %% ## Annotations | evernote 2016.04.25 If habitat quality for a wildlife species is a measure of the importance of habitat type in maintaining a particular species, habitat quality should be defined in terms of the survival and production characteristics, as well as the density, of the species occupying the habitat. The foundation of any wildlife habitat management plan is the ability to assess habitat quality accurately. Without this key ingredient, the effort put into carefully prepared objectives and elegant categorizations of habitat types is largely wasted. Another example of a procedure at this 2nd level of resolution is the USFWS HEP (Flood et al. 1977). This procedure relies on assessment of habitat requirements of individual species taken from the literature, followed by assessment of habitat types based on the ability of each type to provide for these requirements. The two major problems with this approach are that our knowledge of species requirements is often poor and synergistic effects among resources are ignored.  It has been suggested that the accuracy of any habitat rating technique, such as HEP, should be tested by comparing habitat ratings to the observed relative abundances of a variety of wildlife species (Whelan et al 1979.) The assumed positive correlation of a species' abundance with habitat quality underlies most methods used for accessing habitat quality and is explicit for the species-specific level of resolution...The assumed relationship often breaks down...: Habitat use, especially in northern climates, in winter is critical, whereas most surveys are taken in warmer months. For northern deer, the availability of winter range may contribute disproportionately to carrying capacity (and thus survival and reproductive patterns) (Wallmo et al 1977).There may be multi-annual variability in local population densities that reflects small-scale variability in the food source, in predator populations, or in abiotic environnmental factors. For instance, site tenacity in breeding passerines can produce local densities that reflect past, rather than current, habitat quality.Social interactions may prevent subdominant animals from entering what is actually high-quality habitat, while at the same time suppressing reproduction in the high-quality habitat (although one may argue that this in fact does reflect habitat quality in terms of species success, see [[garshelis_2000]]). Fitness of an individual animal (Fisher 1930) is a relative measure that increases with increasing survival probability and increasing offspring reproduction.  I propose that habitat quality be defined as the product of density, mean individual survival probability, and mean expectation of future offspring for residents in one area as compared to other areas. In an extreme example, one could imagine a population where every individual immigrated and none emigrated or reproduced; the quality of the habitat would be zero.  Given this definition of habitat quality, the minimum viable population size will be greater in low-quality than in high-quality habitat, because low survival and reproduction rates in low-quality habitat mean that a higher density is needed to ensure persistence of the species in that habitat.  To measure habitat quality, one must determine the mean production and survival characteristics of each age-class and the number of resident individuals in each age-class in each habitat. Such a determination will be impractical for most studies. The above formula is thus presented to clarify the definition of habitat quality and provide an ideal standard.  Density-based estimates could be greatly improved through attention to immigration patterns, survival, and to production of juveniles that survive to reproduce. An accurate assessment of habitat quality requires the calculation of a grand mean and variance over several time periods. The number of time periods required for a useful measure of habitat quality will be greater for highly unpredictable habitats. Decoupling of habitat quality-density relationship is possible in three main environmental types - Highly seasonal habitat in which different habitat types may be preferred at different seasons - Unpredictability over time (e.g., overflow of populations into lower quality habitat) - Patchiness of habitats (such that overflow is possible) & three main species characteristics - social pattern of dominant interactions (primarily vertebrates) - high reproductive capacity - habitat generalists Intensive multi-annual demographic study of a single species over the range of habitats being measured is needed to interpret the broader surveys \[of species density and habitat quality\] Management plans adopted on the basis of a species survey or census taken during only one year, or on the basis of measured habitat characteristics coupled with inadequate knowledge of the factors actually determining habitat quality are particularly unsatisfactory. %% end annotations %% %% Import Date: 2024-08-15T10:45:29.776-06:00 %%