Suitability of lands for amphibians habitat

Amphibians, like all the other wild animals, while playing their important role in the ecosystem and supporting biological balance, suffer from human actions. Among their troubles are habitat loss and fragmentation, diseases, invasive species, light pollution, and, as animals that highly depend on water, they are the first to suffer from the pollution of the rivers, lakes, and stormwater. The goal of this project was to look at the condition of amphibians' habitat in Los Angeles County and to find places of their possible presence and undesirable interactions with humans.

Methodology

Only species that lay eggs in water and go through the aquatic larval stage were chosen for the research as they have definite enough needs in terms of habitat. Among observed in the area are: Baja California tree frog, California tree frog, Western toad, California newt, California toad, Southern mountain yellow-legged frog, African clawed frog, California red-legged frog, Western spadefoot, Northern leopard frog.

Polluted waterways, busy roads, and developed areas were included as stress factors for amphibians which worsen the suitability of their habitat. They were given a negative weight in the computation of habitat suitability. The land cover was classified according to suitability for amphibians habitat, given that wetlands, forests, and grasslands are perfect places for them to live, while pastures and cultivated crops are less suitable as pastures lack hiding places and debris for water to accumulate under and crops are treated with insecticides and pesticides which are known to have a horrible effect on amphibians existence. Areas around the water were given an extra point in the classification because the studied animals do not travel far away from them and also spend a significant part of their lives in water hatching eggs and growing out from larvae. Only rivers and streams flowing on the surface were selected, marine wetlands were excluded. The great area on the upper right part belongs to the desert ecosystem where the terrain is unsuitable for water-dependent amphibians and includes the desert part of the hydrological system where many lakes are actually saline and dry. That is why this area is given a negative weight for the computation.

Result

The map presented above is the result of the computations. The cell size of the layer is 30x30 meters, and the layer covers the territory of ~112 kilometers around the central point of LA County. The area is classified into 5 types according to suitability for amphibians' habitat.

  • Class 5 is the best and necessary conditions — it can be met around clean rivers and lakes and in the wetlands.
  • Next, the 4th class consists mostly of forests, grasslands, and shrub.
  • The 3rd class is mostly presented by cultivated crops and open spaces like private house backyards and parks
  • A large part of the second class is taken by the desert — it is naturally unsuitable for amphibians. Another contribution is made by developed areas.
  • The worst places for amphibians to be are around roads, polluted rivers, and in places that combine all the stress factors.

This way, the invasion of human activities is seen clearly. Urbanized areas surround forested mountains, dividing the natural areas into barely connected or disconnected parts. Highways strengthen this effect by creating borders between these parts completely insurmountable by tiny amphibians. So even mountains, that seem to be an ideal habitat for any wild animal, are in fact crossed by multiple highways.

Amphibians observed in the area

Available data on the presence of amphibians in the area is provided by Reptiles & Amphibians of Southern California project. We should remember that the data can have imprecisions and even deliberately obfuscated coordinates.

“Urban” species

Things happening in the wild areas are expected — there are unmistakably observable concentrations of animals, especially along the rivers.

However, the most interesting situation is probably in the urban area where amphibians were met too. Zooming in, we can see that they mostly stay in the “oases” of nature in the city — big parks, natural reserves, and conservation areas but also can be met around the city. Please notice a marvelous group of Baja California Tree Frogs in the Madrona Marsh Preserve and in Canada de Palos Verdes Creek. Even though these protected areas seem like good places for amphibians to live, the problem is that they are an example of a completely disconnected habitat — isles of natural land cover surrounded by traffic, noise, and human presence. It gives no chance for migration and breeding with species from another pond.

In general, amphibians seem to be found in places not severely intruded by humans as most of them have higher habitat classes.

Distribution of habitat suitability counts among amphibians’ observations. The histogram is skewed to bigger numbers which means amphibians were mostly met in habitat suitable for them. Also, such a distribution of classes helps make sure that the classification is right.

Interactive map

https://arcg.is/18ie4v
You can take a closer look at the variables in this interactive web map, and play with layers.

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