The landscape looks different whether you look at it through the eyes of a frog, or a lizard, or a human being. Different species have unique responses to the same landscape variables, which can become a challenge when trying to preserve biodiversity in a fragmented landscape. What kind of management recommendations can be made when the landscape is being filtered through so many different lenses?
Many different conceptual models have been devised to predict how species will respond to fragmented landscapes. They often focus on the idea of isolated patches nestled within a matrix, although with varying outcomes.
For example, if only island biogeography theory is applied, empirical studies may focus only on large patches of suitable habitat and ignore the surrounding matrix. Conversely, using matrix models may lead to management recommendations that manipulate surrounding matrix rather than patches themselves. How biodiversity is preserved can then be dependent not on the best methods, but rather the initial bias of the conceptual model.
New research not only assesses multiple landscape conceptual models at once, but does so across multiple species to see how these models compare in their predictive ability. Researchers tested which models most accurately predict the response in abundance and species richness of frogs and reptiles in remnant box gum grassy woodlands, a critically endangered ecosystem community in southeastern Australia.
The five landscape conceptual models tested included:
- Island biogeography theory – species occur in remnant patches surrounded by a “sea” of inhospitable matrix
- Continuum model – species respond to environmental gradients (e.g. food, shelter, space, climate) in a species-specific, continuous manner
- Habitat Amount hypothesis – species richness is most influenced by the total amount of available habitat, rather than patch size or patch amount
- Matrix Tolerance model – a species’ ability to tolerate the matrix influences its abundance in patches and ultimately predicts how likely they are to persist under human modification
- Matrix Quality model – the type of matrix is most important for determining species persistence
So how did each model fare?
Island biogeography theory was least effective in predicting responses, and likely provides an overly simplistic view in assuming that the matrix is totally inhospitable. The Continuum model provided useful insights into how gradients of key factors influence the species and community responses, but responses varied across environmental variables and scale. The Habitat Amount hypothesis provided contradictory results for reptiles and did not conform to predictions for all but one frog species. Predictions of both the Matrix Tolerance model and the Matrix Quality model were supported, confirming the overall message that a species’ ability to use human-modified land cover increases the ability of the species to persist in highly modified landscapes, and that the type of human land use has a strong influence on spatial patterns of biodiversity.
The key lessons are that many species are likely responding to gradients of environmental conditions, and human-modified landscapes are less a discrete patch-matrix system and more a fluid mosaic of different habitat types. Using multiple landscape conceptual models can then provide complementary frameworks for discussing species’ response to fragmentation and formulating appropriate management actions.
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