The Peruvian Andes are a biodiversity hotspot with 25 000 species of plants, 700 bird species, 450 mammal species and 2000 fish species. While most of these are in the Amazonian (East) side of the Andes, the West side has its fair share of this diversity, mainly in its vast montane forests. Of these species, 122 are threatened due to land use change, deforestation, melting glaciers and drought (local climate change). When exploring the biodiversity gradient of the Andes, it is important to understand the concept of species richness which is the total number of species in a particular total area. This paper will explore the general relationship of biodiversity and elevation, how landscape changes have shaped the biodiversity of the Marañón valley and Andean ecosystems at risk.
Considering that the West Peruvian Andes are generally a desert ecosystem, many of the species that reside there have evolved adaptations for water conservancy and extreme temperatures. Temperature poses direct physiological constraints on many organisms as well as indirect constraints through food and resource availability. Many plants cannot grow in extreme aridity, however the plants that do grow, have adapted to the lack of moisture through the development of a variety of mechanisms including succulence, wide spacing (to reduce competition for moisture), allelopathy, deciduous habits, thorns, and rapid life cycles. Insect abundances are also limited by water availability, as many need small pools of water to lay eggs or for larvae to grow.
Water availability and temperature are therefore the primary influences on species richness, as the physiologies of organisms are adapted to particular ranges of conditions and their food (plants and insects) are also constrained by water and temperature. The water and temperature gradients of the West Peruvian Andes can be observed in Figure 1. Peak in water availability (precipitation), as determined by McCain (2006) is at approximately 1500 -2000m, and in many cases, species richness also peaks at this elevation. Below is an example of how bat species richness in the Andes is influenced by the temperature and water availability gradients.
Species diversity in the Marañón valley contains a very high level of endemic species richness, mainly in terms of plant species. In a study conducted by Särkinen et al. (2011), it was found to harbor nine endemic Mimosa species and about three more widespread species with their distribution shown below. This valley is also home to many endemic species of Inca-finches, scaled lizards, land snails, and harlequin frogs. Distribution of these species appears to be fragmented, with species occurring in isolated patches. When observing and comparing the phylogenetic trees of Andean Mimosa, as well as Coursetia, Poissonia, and Cyathostegia, the sequence divergence patterns and the presence of monophyly (each taxa containing all descendants of a single common ancestor in the narrowly restricted) in geographically isolated species suggests that these species have been isolated for a long time, but all originated from the same area. This is referred to as geographic speciation, in which physical isolation is the key component in splitting the single ancestor into two species. In addition, Särkinen et al. (2011) observed high local endemism, as well as high elevation habitats fostering narrowly restricted species. These results suggest that the species diversification over large time scales was largely driven by landscape features isolating populations, specifically the high Andean Cordilleras.
As mentioned above, although the Peruvian Andes are home to a vast number of species, many are endangered. In Peru, ~75% of endangered species are protected by one of many national and international agreements and treaties that Peru is involved with. The Marañón valley has been deemed a biodiversity hotspot of global conservation priority because of its high number of endemic fauna and flora, but its dry forests are still largely unprotected. These species are at risk mainly because of human-induced climate change.
Climatic studies of Peru and surrounding areas, have shown that general conditions are shifting toward being warmer and drier. Shifts in precipitation patterns and type of precipitation (solid, liquid or mist) could cause increased erosion and landslides in some places, and severe drought in others. These changes will likely affect the abiotic functions of ecosystems as well as ecosystems that span the steep slopes of the montane or cloud forests. Cloud forests are particularly vulnerable, because the structure and functioning of the ecosystems are dependent on the level of cloud bases, which is predicted to shift with climate change. Rising cloud bases could lead to decreased moisture in some areas. This has severe consequences on epiphyte species that have evolved epiphytic characteristics because of abundant moisture. These effects do not occur in isolation, as collapse of the base of the food chain (plants) tends to lead to trophic cascades.
In terms of aquatic ecosystems, rising temperatures and lower precipitation levels could result in diminished wetlands and lower dissolved oxygen levels. High temperatures will reduce the capacity of water bodies to dissolve oxygen, leading to increased mortality of many organisms with narrow temperature ranges organisms. As wetlands dry up, the habitat of many species is destroyed and they could even shift from carbon sinks to become potential carbon sources, further amplifying the effects of climate change.
Changes in the physical environment could also lead to contractions or expansions in species ranges in terms of area, and disappearance or migration of species. A recent study by von May et al. (2008) showed three frog species expanded their historical ranges to higher elevations because of recent de-glaciation, while three other species migrated to other areas. Species shifting ranges and relocating themselves will have many (unknown) effects on ecosystems structure and functioning. It also leads to the creation of many no-analog ecosystems, for which there are many uncertainties about whether or not functional roles of shifting species will be replaced by new species migrating into ecosystems.
Biodiversity of the Peruvian Andes has always been and will continue to be shaped by the climatic conditions (temperature and precipitation) and landscape features. Current climate change continue to put pressure on many ecosystems, particularly ecosystems that contain organisms with narrow temperature ranges and low resilience. Further climate changes could lead to changes in the landscape features and continuity, leading to isolation or even uniting of previously isolated species, highlighting the immense dynamism of these ecosystems.
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McCain, C. M. (January 01, 2007). Could temperature and water availability drive elevational species richness patterns? A global case study for bats. Global Ecology and Biogeography, 16, 1, 1-13.
Sarkinen, T. E., Simon, M. F., Hughes, C. E., Marcelo-Pena, J. L., Daza, Y. A., & Toby, P. R. (February 01, 2011). Underestimated endemic species diversity in the dry inter-Andean valley of the Río Marañón, northern Peru: An example from Mimosa (Leguminosae, Mimosoideae). Taxon, 60, 1, 139-150.
von May, Rudolf, et al. “Current state of conservation knowledge on threatened amphibian species in Peru.” Tropical Conservation Science 1.4 (2008).