Islands harbor a large part of the world's threatened biodiversity, mostly due to the degradation and loss of habitats, the exploitation of natural resources, and the introduction of invasive alien species. Understanding how island communities are assembled and how they function will help prevent the loss of this valuable biodiversity, which consists not only of a list of species, but also of the interactions among them. Islets (with an area <3 km2) can be considered biodiversity sanctuaries: many species and interactions can only survive in them, as they tend to suffer less anthropogenic disturbances than larger islands. Islets can actually be considered potential reservoirs for future translocations and reintroductions of locally extinct species in larger neighbour islands, and they function as well as refuges of vulnerable interactions.
The main objective of our project (ISLET-FOODWEB) is to study the structure of the entire trophic network of different islets belonging to six different archipelagos of the world. One ultimate goal of our project is to identify the inflection point beyond which the functioning of the islet ecosystem can collapse due to a disturbance, such as the loss of a key species. For this we’ll also use a network approach, genetic tools to identify mycorrhizal fungi, and ecological modeling to simulate different extinction scenarios. In this blog, we’ll start by telling you what we have been doing and finding in Daphne Major, of the islets we have chosen for this project.
The main objective of our project (ISLET-FOODWEB) is to study the structure of the entire trophic network of different islets belonging to six different archipelagos of the world. One ultimate goal of our project is to identify the inflection point beyond which the functioning of the islet ecosystem can collapse due to a disturbance, such as the loss of a key species. For this we’ll also use a network approach, genetic tools to identify mycorrhizal fungi, and ecological modeling to simulate different extinction scenarios. In this blog, we’ll start by telling you what we have been doing and finding in Daphne Major, of the islets we have chosen for this project.
The core team of the project is constituted by Anna Traveset, Research Professor of the Spanish Research Council (CSIC) at IMEDEA, and leader of the expedition; Manuel Nogales, Scientific Researcher of CSIC at IPNA (Tenerife, Canary Islands); Ruben Heleno, Researcher at the University of Coimbra (Portugal); and Sandra Hervías, Post-doctoral researcher at IMEDEA. In the first expedition to Daphne we were accompanied by Roberto Jiménez and in the second by Carlos Vera, both belonging to the staff of the Galapagos National Park (GNP).
Daphne Major is a 34ha island at the heart of the Galapagos archipelago in the Pacific ocean. It is the island where Peter and Rosemary Grant conducted one of the most outstanding natural experiments, monitoring an entire community of finches for over 40 years, that allowed them to see ‘evolution in action’.
The bird populations are thus very well known after so many expeditions by ornithologists, but not so the rest of biodiversity. So we hope to find many new species, mostly invertebrates, not yet cited in this island.
The first expedition is from November 16th to 20th 2018, during the dry season, whereas the second is from March 29th to April 2th 2019, at the peak of the rainy season. Thus, we are five days each time on the island. We believe it is enough time to record many interactions taking place in each period in such small area by five people. Moreover, conditions are hard in this uninhabited island, and we think it is a reasonable time to endure without taking a shower! Note that we cannot have a swim here, as there are no beaches, plus the island is surrounded by abundant sharks (that we can easily see!) waiting for some of us to fall into the water!
We get to Daphne around 08:00 am with one of the boats of the PNG, The Ranger I, which we have boarded in the Itabaca channel.
There is only one place to disembark in the entire islet and it is the one we use! It is not much difficult, compared to other islets in which we have disembarked, but is slippery and the slope is strong.
There is no much shade in the island, so we have to use one of the caves that we’ll use as our kitchen for the next 5 days. We feel sorry to bother a sea lion that was sleeping in the cave and must now leave to another one…
Later we go up to the crater and there we install our tends, in the craterlet. We’ll share this ‘plaza’ with a family of frigate birds.
In the November expedition, we assume that it is a relatively normal dry season, in which it has rained very little. Our first impression is that there is 'little life' on the island. We see a basically gray landscape on which only the green of the Opuntia, the red of Sesuvium, and the white of the guano of the marine birds stand out. When we come back in March, the landscape is a bit more greenish but not so much as we expected, given that in February it had rained for several days.
Along the entire coast we see Nazca boobies (there is a large colony on the island, possibly around 200 individuals?) preparing the nest, although we also see offspring in some of these. Blue-footed boobies are very scarce in Daphne Major. In March, the nests will have either eggs (1 or 2) or fledglings.
We are also struck by the large number of bird carcasses (especially marine) found throughout the island, especially frigates, but also Nazca boobies, pelicans, tropical birds, petrels, terns, finches (some of the latter are ringed by the Grant couple; we find at least 4 individuals of the large fround finch (Geospiza magnirostris!), and also of the barn owl (Asio flammeus).
We are also struck by the large number of bird carcasses (especially marine) found throughout the island, especially frigates, but also Nazca boobies, pelicans, tropical birds, petrels, terns, finches (some of the latter are ringed by the Grant couple; we find at least 4 individuals of the large fround finch (Geospiza magnirostris!), and also of the barn owl (Asio flammeus).
Here and there we see lots of lizards, Microlophus indefatigabilis, some on the plants, others searching for food on the ground, and others even approaching the sea lion droppings to see what they can get there!
We install the Malaise trap to capture insects, as well as the mist nests to capture birds.
The first day we capture no insects with this trap. With the mist nets we do capture about 20 finches and one dove. We measure them, ring them, and gather samples from their beaks to assess whether they carry pollen grains. We also get their droppings in the bags we keep them for a while until they defecate.
We wake up at 06:00 and open the mist nets again. We capture some more finches. Sometimes it is not easy to identify to the species level. In these cases we take pictures and will check more carefully later on.
Our plan today is to start working on the eight transects we have drawn through the islet. In these transects (100 m long) we’ll measure vegetation cover, plus we’ll obtain the invertebrate samples (spinning stones and gathering all alive and dead animals).
Moreover, we begin censusing pollinators on the 10 flowering species we have found in November. We aim at doing censuses of 1 hour per species. In March, the number of plants in flower are much higher (XX species).
At night we take our lanterns and go to see what is going on in ‘dark conditions’. We see abundant scorpions, and geckos! We have also set up a light trap and we hope it will attract moths and nocturnal insects.
We have found many insects in our light traps, many small moths but also beetles and ants. We begin capturing lizards to get their scats and we also sample whether they carry pollen i their snouts. We employ the same method as for birds, using glicerogelatine to trap the pollen grains which we’ll later identify under the microscope in the laboratory. In about an hour, we have collected 15 individuals! We mark them with nail paint to avoid re-capturing the same individuals. We have become real experts capturing lizards with our ‘fishing ties’ We collect too, lizard dropping from all over where we find them. Identifying what is in them is crucial to know their diet. We also collect from all over the island, all bird regurgitations we find. In the owl nests, such regurgitations are common, usually full of bird bones. We search in all caves we find as owls are usually found there. At night, a curious owl wants to stay with us in the camp.
We keep working on all the different tasks we must finish (censusing pollinators, capturing birds, lizards, picking lizard and gecko droppings, etc. ). We keep finding interesting interactions, also on herbivory: birds and lizards eating flowers and fruits of Chamaesyce and Tiquilia, doves feeding upon Opuntia seeds, large ground finch searching for beetle larvae in the branches of Bursera, etc.
Time to pack everything, although we keep finishing censusing pollinators on some of the plant species. We leave Daphne around 13:30. It has been a very fruitful expedition. We have collected lots of material and lots of interactions to start building the trophic web of this little interesting islet!