Home to Darwin’s famous first experiments on natural selection, the Galápagos Islands have a high number of unique and precious plant and animal species. However, a new study in this August’s Ecology by conservation biologists Alejandra Restrepo, Paul Colinavaux, and their colleagues found that the ecosystem of these islands, specifically the vegetation, has been altered due to climate change and human action.
Restrepo and Colinavaux’s team, made up of biologists from such organizations as the Charles Darwin Foundation and the Florida Institute of Technology, argue that human interaction in combination with global climate change patterns has contributed to a loss in plant species and a shakier balance of native plant populations. As a result, humans may have contributed to the irreparable destruction of the Galápagos’ unique ecosystem.
Curious about the effect of warmer temperatures and human factors on the Galápagos, researchers working with Restrepo and Colinavaux began to study the east island of San Cristobal, specifically El Junco Crater Lake. The only freshwater lake on the island, this lake was ideal to study due to the endemic plants found only there as well as historically noticeable effects from El Niño and La Nińa weather events. This allowed the scientists to test the effects of more intense rainy seasons and droughts due to climate change, comparing older and newer data. Researchers then set out to gather a pollen record of the plants inhabiting El Junco Lake. The pollen record allowed the scientists to compare recent success and spread of plant species affected by global warming and humans with ancient, fossilized pollen records before these factors. Pollen samples dating back up to 2690 years ago were collected around the lake and the team analyzed trends in pollen type over time, hoping to discover the effects of climate change on plant species.
Restrepo and Colinavaux’s findings certainly reflect the influence of warmer temperatures and stronger climate patterns such as El Niño on plant populations in the island. For example, the plant Croton scouleri needs abundant light to successfully survive and reproduce. The research team found a peak amount of Croton pollen spread in recent years, suggesting that harsher El Niño effects in the Galápagos have favored plants that require lots of light as opposed to other species. Furthermore, the researchers found increasing pollen around the lake from the Hippomane, Cryptocarpus, and Bursera species. This finding appears abnormal given that all three are non-native to the area and require transport by convection winds to the lake. Increased weather events caused by warming ocean waters have resulted in greater spread of non-native plants in areas of the Galápagos, altering the ecosystem perhaps for good.
The impact of human activity on plant species is not forgotten by the report. As humans have inhabited and interfered with the Galápagos, habitats have been destroyed and fragmented as well as invasive plant species introduced. From the pollen record, researchers noted that the plants Acalypha and Alternanthera, formerly significant producers of pollen, have been overtaken by invasive plant species since 1930. This decline can be tied to human action when considering that following 1800, humans introduced grazing animals and foreign seeds. As livestock favor the Acalypha plant, population numbers of Acalypha plummeted as foreign species took over. The grazing and roaming of animals also may have contributed to the spread of new species in areas where they were formerly absent, altering the local ecosystem.
In the future, the biologists argue that the effects of global warming and human intervention in the Galápagos should be actively improved, if not already permanent. Efforts are already underway to remove invasive species and grazing animals have been restricted. Despite this the stability of the islands’ ecosystem remains under question, as scientists are unsure of how much variation the new environment can sustain. Furthermore, the findings assert that human actions such as introduction of species are more significant than previously thought, even surpassing the influence of past climate change on the islands. From this study it seems clear that human interaction with delicate environments has many unforeseen consequences. In order to protect the plant species of unique geographies such as the Galápagos, both climate change and detrimental human actions must be mitigated.
Restrepo, Alejandra, Paul Colinvaux, Mark Bush, Alexander Correa-Metrio, Jessica Conroy, Mark R. Gardener, Patricia Jaramillo, Miriam Steinitz-Kannan, and Jonathan Overpeck. 2012. Impacts of climate variability and human colonization on the vegetation of the Galápagos Islands. Ecology 93:1853–1866.