**7. Ecological parameters and models developed**

**SPECIES SUBSTRATE**

*Hanseniaspora guilliermondii* Flower *Pichia nakasei* Rotten Wood *Saturnispora quitensis* Insecta *Candida pseudolambica* Excrement *Kluyveromyces marxianus* Rotten vegetal

*Trichosporon dermatis* Fruit *Hanseniaspora valbyensis* Leaf

(c)

**Figure 3.** (a) Shared species between Galápagos Islands and Mainland Ecuador and its occurrence in different sub‐ strates; (b) Species found in Galápagos and the substrates these yeast colonize; (c) Species found in Ecuador Mainland

*Candida boidinii Candida apicola Metschnikowia reukaufii Candida glabrata Trichosporon jirovecii Candida ecuadorensis Candida oleophila Candida gigantensis Candida pomicola Cryptococcus albidus Metschnikowia koreensis* 

218 Biodiversity - The Dynamic Balance of the Planet

*Pichia fabianii* 

*Rhodosporidium babjevae Rhodotorula slooffiae Hanseniaspora opuntiae Candida sorboxylosa Candida xylopsoci Candida boleticola Sporidiobolus ruineniae Candida carpophila Candida bombi Clavispora lusitaniae* 

and the substrates these yeasts colonize

The degree of specialization of a yeast species is given by its metabolic abilities and tolerance to environmental factors such as UV radiation [40], inhibition substances and even microbial predators [34], etc. Leaves are exposed to fluctuations of temperature and relative humidity values, which may have an impact on the yeast communities. Large fluxes of UV radiation are also one of the most prominent features of the leaves, fruits and other substrates in the environment to which microorganisms have presumably had to adapt [21, 51]. Many plants contain a number of compounds whose adaptive significance may be a defense against invertebrates and microorganisms; for instance, all parts of *Datura* sp. contain toxic belladonna alkaloids, the concentration of which is highest in the petioles of the flowers [52]. These compounds also act, in some cases, as selective agents which shape the yeast community composition [53].

The yeasts which are highly adaptable to different ecological niches—like *Candida tropicalis* are the ones that display a wide range of responses and developed defense strategies [45]. This particularly abundant and cosmopolitan yeast species is the most frequently isolated in mainland and in the islands according to CLQCA database. This yeast species has been found in flowers, rotten wood, insects, excrement, rotten vegetal matter, and fungus (Figure 3a). *Candida tropicalis* has been reported to grow even at pH so high as 10 [41], which is a remarkable feature in terms of tolerance facing unusually hard environmental conditions.

On the other hand there are yeasts that show a narrower repertoire of metabolism and even metabolic deficiencies such as *Saccharomycopsis fodiens*, a predacious yeast species that is deficient in sulfate uptake and require supplementation of organic sulfur sources [54]. This yeast species is highly specialized in predation of other yeasts and fungi. Nevertheless it appears to be quite rare in the environment and very few is known about its natural history and ecology. Only three isolates from Costa Rica, Australia and the Galápagos islands were found so far. A further expedition in Taiwan registered other isolates of this species associated to *Drosophila* flies [34].

#### **7.1. How the ecological niches are occupied by yeasts in mainland and the islands?**

It is certainly ventured to establish in an accurate way the ecological relationships of yeasts in the islands and the mainland with general data and relatively few samples. For this report we have addressed this issue by means of a global comparison of yeast species number that has been found in different substrates both in mainland and the islands. Despite the kind of substrate, we marked the repetitions of registers in substrates from each one of the species. This analysis gave us a general scheme of the degree of adaptation that is currently facing the yeasts.

In Figure 4 it is seen the general state of the yeasts based on the number of substrates they occur. This analysis was performed on those species found in mainland and the islands and those which are represented in both ecosystems.

species.

No endemism has been studied or detected in this survey. There is only one yeast isolate representing a hitherto non described species, this is *Lindnera* sp. that was collected from

An Overview of the Yeast Biodiversity in the Galápagos Islands and Other Ecuadorian Regions

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221

The fact that in mainland the competition for substrates may be much more intensive than in the islands [16] could lead to shape more generalist yeast communities, while in the islands the yeasts species show a different trend that may be explained by a lower competence level

From the data obtained in this work, it has been developed a simple model of calculation which allows us to establish the Index of Abundance (*Ia*) which is understood as the product of the total ecosystems where the species has been registered and the total different substrates that the species is able to colonize. The index maximum value is 1 and minimum is 0. The equation

Where *Ia* is the Index of Abundance; *Sc* is defined as the substrates colonized by the species; *O* is the occurrence in the different ecosystems that are being analyzed; *Sm* is the maximum number of substrates analyzed in the survey; and, *Om* represents the maximum occurrence and is equal to the total number of ecosystems analyzed (seven ecosystems in the case of this study).

The *Ia* provides figures to compare the relative abundance of each yeast species in the ecosys‐ tems. Moreover it gives an idea about the generalist species, where the higher the *Ia*, the lower

On the other hand, it is also necessary to define the extent of specialization of each yeast species.

is defined as the Index of Specialization; and *Ia* is the Index of Abundance.

of seven ecosystems and 10 substrates (no yeast have been collected in all the substrates). It can be seen that *C. tropicalis* has been found in nine of 10 substrates compared in this survey,

occurrence and 0 means the lack of register of the species in the particular substrate. The

number of substrates colonized by the species was taken from Figure 3a, 3b, and 3c.

*Si* <sup>=</sup> -**log**<sup>10</sup> *<sup>I</sup> <sup>a</sup>*

) is calculated from the following equation (3):

are inversely proportional to those of *Ia* given that the higher the abundance,

calculations can be seen based on the data from CLQCA and the analysis

(*Sm*\**Om*) (2)

<sup>2</sup> (3)

*.* The number 1 represents the positive

*Ia* <sup>=</sup> (*Sc*\**O*)

*Scalesia* sp. rotten wood. This genus of tree is endemic to the Galápagos Islands.

and lower diversity in terms of ecological niches as compared to mainland.

**7.2. Yeast specialization in Ecuadorian environments**

(2) to calculate such index is as follows:

the specialization (more generalist species).

being the species with the higher *Ia* and lower *Si*

The Index of Specialization (*Si*

the lower the specialization.

Where *Si*

The values of *Si*

In Table 6 the *Ia* and *Si*

represented by various yeasts that are able to colonize up to 9 different substrates. Only 1 yeast species looks confined to one kind of substrate. In the case of the species found in **Figure 4.** Global comparison in terms of adaptability to different substrates of yeast species.

mainland exclusively, the figures are different, since the adaptability to various substrates looks lower, while the colonization of a single substrate is higher than the previous case, namely 22 yeasts occupy only one kind of substrate. As for the Galápagos yeasts the degree of adaptability is seen in more species but the specialization is much higher than in the before mentioned cases, this is 30 yeast species are confined to one specific substrate. The yeast species shared between Galápagos and the mainland are mostly generalistic and show a wide range of substrates as ecological niches occupied. In contrast, the majority of the yeast species which have been found exclusively, both in the islands and the mainland, is less generalistic and occupy a narrow range of substrates. In other words, we can see that those yeast species which are more adapted to the mainland and the island ecosystems will probably find some ecological barriers that may impede the colonization of those Noteworthy, those yeast species which are common to Galápagos and mainland are repre‐ sented by various yeasts that are able to colonize up to 9 different substrates. Only 1 yeast species looks confined to one kind of substrate. In the case of the species found in mainland exclusively, the figures are different, since the adaptability to various substrates looks lower, while the colonization of a single substrate is higher than the previous case, namely 22 yeasts occupy only one kind of substrate. As for the Galápagos yeasts the degree of adaptability is seen in more species but the specialization is much higher than in the before mentioned cases, this is 30 yeast species are confined to one specific substrate.

**Figure 5.** Global comparison in terms of adaptability to different substrates of yeast

Noteworthy, those yeast species which are common to Galápagos and mainland are

ecosystems which they do not belong to. This can be regarded as a disharmony example. No endemism has been studied or detected in this survey. There is only one yeast isolate representing a hitherto non described species, this is *Lindnera* sp. that was collected from *Scalesia* sp. rotten wood. This genus of tree is endemic to the Galápagos Islands. The fact that in mainland the competition for substrates may be much more intensive than in the islands [16] could lead to shape more generalist yeast communities, while in the islands the yeasts species show a different trend that may be explained by a lower competence level and lower diversity in terms of ecological niches as compared to mainland. **Yeast specialization in Ecuadorian environments**  From the data obtained in this work, it has been developed a simple model of calculation The yeast species shared between Galápagos and the mainland are mostly generalistic and show a wide range of substrates as ecological niches occupied. In contrast, the majority of the yeast species which have been found exclusively, both in the islands and the mainland, is less generalistic and occupy a narrow range of substrates. In other words, we can see that those yeast species which are more adapted to the mainland and the island ecosystems will probably find some ecological barriers that may impede the colonization of those ecosystems which they do not belong to. This can be regarded as a disharmony example.

which allows us to establish the Index of Abundance (*Ia*) which is understood as the product of the total ecosystems where the species has been registered and the total different No endemism has been studied or detected in this survey. There is only one yeast isolate representing a hitherto non described species, this is *Lindnera* sp. that was collected from *Scalesia* sp. rotten wood. This genus of tree is endemic to the Galápagos Islands.

The fact that in mainland the competition for substrates may be much more intensive than in the islands [16] could lead to shape more generalist yeast communities, while in the islands the yeasts species show a different trend that may be explained by a lower competence level and lower diversity in terms of ecological niches as compared to mainland.

#### **7.2. Yeast specialization in Ecuadorian environments**

**Figure 5.** Global comparison in terms of adaptability to different substrates of yeast

**Adaptability of yeast to substrates**

Species found in Mainland and Galápagos Species found only in Galápagos

Species found only in Mainland

0 1 2 3 4 5 6 7 8 9 10

**Number of Substrate**

**Figure 4.** Global comparison in terms of adaptability to different substrates of yeast species.

Noteworthy, those yeast species which are common to Galápagos and mainland are represented by various yeasts that are able to colonize up to 9 different substrates. Only 1 yeast species looks confined to one kind of substrate. In the case of the species found in mainland exclusively, the figures are different, since the adaptability to various substrates looks lower, while the colonization of a single substrate is higher than the previous case, namely 22 yeasts occupy only one kind of substrate. As for the Galápagos yeasts the degree of adaptability is seen in more species but the specialization is much higher than in the before mentioned cases, this is 30 yeast species are confined to one specific substrate. The yeast species shared between Galápagos and the mainland are mostly generalistic and show a wide range of substrates as ecological niches occupied. In contrast, the majority of the yeast species which have been found exclusively, both in the islands and the mainland, is less generalistic and occupy a narrow range of substrates. In other words, we can see that those yeast species which are more adapted to the mainland and the island ecosystems will probably find some ecological barriers that may impede the colonization of those ecosystems which they do not belong to. This can be regarded as a disharmony example. No endemism has been studied or detected in this survey. There is only one yeast isolate representing a hitherto non described species, this is *Lindnera* sp. that was collected from

Noteworthy, those yeast species which are common to Galápagos and mainland are repre‐ sented by various yeasts that are able to colonize up to 9 different substrates. Only 1 yeast species looks confined to one kind of substrate. In the case of the species found in mainland exclusively, the figures are different, since the adaptability to various substrates looks lower, while the colonization of a single substrate is higher than the previous case, namely 22 yeasts occupy only one kind of substrate. As for the Galápagos yeasts the degree of adaptability is seen in more species but the specialization is much higher than in the before mentioned cases,

*Scalesia* sp. rotten wood. This genus of tree is endemic to the Galápagos Islands.

level and lower diversity in terms of ecological niches as compared to mainland.

**Yeast specialization in Ecuadorian environments** 

do not belong to. This can be regarded as a disharmony example.

this is 30 yeast species are confined to one specific substrate.

The fact that in mainland the competition for substrates may be much more intensive than in the islands [16] could lead to shape more generalist yeast communities, while in the islands the yeasts species show a different trend that may be explained by a lower competence

The yeast species shared between Galápagos and the mainland are mostly generalistic and show a wide range of substrates as ecological niches occupied. In contrast, the majority of the yeast species which have been found exclusively, both in the islands and the mainland, is less generalistic and occupy a narrow range of substrates. In other words, we can see that those yeast species which are more adapted to the mainland and the island ecosystems will probably find some ecological barriers that may impede the colonization of those ecosystems which they

From the data obtained in this work, it has been developed a simple model of calculation which allows us to establish the Index of Abundance (*Ia*) which is understood as the product of the total ecosystems where the species has been registered and the total different

species.

0

5

10

15

20

**Number of Species**

25

30

35

220 Biodiversity - The Dynamic Balance of the Planet

From the data obtained in this work, it has been developed a simple model of calculation which allows us to establish the Index of Abundance (*Ia*) which is understood as the product of the total ecosystems where the species has been registered and the total different substrates that the species is able to colonize. The index maximum value is 1 and minimum is 0. The equation (2) to calculate such index is as follows:

$$I\_a = \frac{(\text{S}\_c \text{\*} O}{(\text{S}\_w \text{\*} O})}{(\text{S}\_w \text{\*} O} \tag{2}$$

Where *Ia* is the Index of Abundance; *Sc* is defined as the substrates colonized by the species; *O* is the occurrence in the different ecosystems that are being analyzed; *Sm* is the maximum number of substrates analyzed in the survey; and, *Om* represents the maximum occurrence and is equal to the total number of ecosystems analyzed (seven ecosystems in the case of this study).

The *Ia* provides figures to compare the relative abundance of each yeast species in the ecosys‐ tems. Moreover it gives an idea about the generalist species, where the higher the *Ia*, the lower the specialization (more generalist species).

On the other hand, it is also necessary to define the extent of specialization of each yeast species. The Index of Specialization (*Si* ) is calculated from the following equation (3):

$$S\_i = \frac{\cdot \log\_{10} I\_s}{2} \tag{3}$$

Where *Si* is defined as the Index of Specialization; and *Ia* is the Index of Abundance.

The values of *Si* are inversely proportional to those of *Ia* given that the higher the abundance, the lower the specialization.

In Table 6 the *Ia* and *Si* calculations can be seen based on the data from CLQCA and the analysis of seven ecosystems and 10 substrates (no yeast have been collected in all the substrates). It can be seen that *C. tropicalis* has been found in nine of 10 substrates compared in this survey, being the species with the higher *Ia* and lower *Si .* The number 1 represents the positive occurrence and 0 means the lack of register of the species in the particular substrate. The number of substrates colonized by the species was taken from Figure 3a, 3b, and 3c.


**AMAZON REGION**

**COASTAL**

**REGION**

**HIGHLAND REGION**

**FLOREANA ISLAND**

**ISABELA ISLAND**

**SAN CRISTOBAL ISLAND**

An Overview of the Yeast Biodiversity in the Galápagos Islands and Other Ecuadorian Regions

**SANTA CRUZ ISLAND**

**OCCURRENCE IN ECOSYSTEMS**

**SUBSTRATES COLONIZED**

**INDEX OF ABUNDANCE**

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**(***Ia***)**

**SPECIALIZATION INDEX**

**(***Si*

)

223


**AMAZON REGION**

222 Biodiversity - The Dynamic Balance of the Planet

**COASTAL**

**REGION**

**HIGHLAND REGION**

**FLOREANA ISLAND**

**ISABELA ISLAND**

**SAN CRISTOBAL ISLAND**

**SANTA CRUZ ISLAND**

**OCCURRENCE IN ECOSYSTEMS**

**SUBSTRATES COLONIZED**

**INDEX OF ABUNDANCE**

**(***Ia***)**

**SPECIALIZATION INDEX**

**(***Si*

)


calculation of *Ia* and *Si*

.

With these data it is possible to obtain a plot *Si*

**AMAZON REGION**

**COASTAL**

**REGION**

**HIGHLAND REGION**

**FLOREANA ISLAND**

**Table 6.** Occurrence in different ecosystems and different substrates of yeast species in Galápagos and Mainland and

bility of yeast species in the ecosystems herein analyzed. Figure 5 shows the curve:

versus *Ia* which provides the curve of Adapta‐

**ISABELA ISLAND**

**SAN CRISTOBAL ISLAND**

An Overview of the Yeast Biodiversity in the Galápagos Islands and Other Ecuadorian Regions

**SANTA CRUZ ISLAND**

**OCCURRENCE IN ECOSYSTEMS**

**SUBSTRATES COLONIZED**

**INDEX OF ABUNDANCE**

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**(***Ia***)**

**SPECIALIZATION INDEX**

**(***Si*

)

225


**AMAZON REGION**

224 Biodiversity - The Dynamic Balance of the Planet

**COASTAL**

**REGION**

**HIGHLAND REGION**

**FLOREANA ISLAND**

**ISABELA ISLAND**

**SAN CRISTOBAL ISLAND**

**SANTA CRUZ ISLAND**

**OCCURRENCE IN ECOSYSTEMS**

**SUBSTRATES COLONIZED**

**INDEX OF ABUNDANCE**

**(***Ia***)**

**SPECIALIZATION INDEX**

**(***Si*

)

**Table 6.** Occurrence in different ecosystems and different substrates of yeast species in Galápagos and Mainland and calculation of *Ia* and *Si* .

With these data it is possible to obtain a plot *Si* versus *Ia* which provides the curve of Adapta‐ bility of yeast species in the ecosystems herein analyzed. Figure 5 shows the curve:

Endangered plant species may also put in danger some insects associated to those endemic plants, since the insect-plant associations generates different degrees of dependence. Studies carried out between 2001 and 2002 showed that 19 endangered plant species exhibit a range of interactions (with different degrees) with 108 different insect species that use the plants as refugee or food. The study carried out by [56] shows that 77% of the insects are endemic. From our studies, insects have shown to be the second source of yeasts biodiversity after flowers. Moreover, studies focused on insect-yeast interactions, have shown a remarkable role of insects acting as "wet nurses" for yeasts during certain periods during the year [57]. Consequently, some yeast species could be endangered along with their hosts who have a tight mutualism

An Overview of the Yeast Biodiversity in the Galápagos Islands and Other Ecuadorian Regions

To date, two novel yeast species collected in this survey were already described (i.e. *Saccharo‐ mycopsis fodiens* and *Kodamaea transpacifica*). Both yeasts species were isolated from nitidulid beetles in ephemeral flowers of *Ipomoea* sp. and *Datura* sp. These species are regarded as biomarkers for ancient migrations of Polinesyan sailors, who took the sweet potato plants (*Ipomoea* sp.) from the Andes (currently Ecuador and Peru) and introduced them into Polynesia

In this chapter we have developed a new ecological approach by means of a mathematical model which is useful for a better understanding of the adaptability of yeasts as well as the specialization degree of these microorganisms in Ecuadorian ecosystems. The data herein processed will be completed in future expeditions, but constitutes a base for the upcoming ecological studies of the yeasts in the Galápagos Islands and Ecuadorian Mainland. The mathematical model shows an inverse correlation between the "Index of Specialization" (*Si*

and the "Index of Abundance" (*Ia*). Moreover, it can be seen that the trend is towards the

to 0.53, which means that they were isolated from a maximum of three out of seven ecosystems and a maximum of three out of nine substrates; 30 yeast species (c.a. 29%) showed an inter‐

of six different ecosystems and six different substrates; finally, only four yeast species (c.a. 4%)

up to seven ecosystems and nine substrates analyzed. These four yeast species are considered the more generalist and exhibit the highest adaptability, but represents a minority in the complete pool of yeast species studied. The total number of ecosystems analyzed was seven and the total number of substrates studied were 10. No yeast species were found in all the 10

Moreover, we have found that in the Galápagos Islands the percentage of yeast species that are colonizing a single substrate is about a 30% higher than the correspondent figure in mainland (Figure 4). We can hypothesize that in mainland the ecosystems have had much more exchanges along the natural history, furthermore, the yeasts species were able to adapt to a wider range of substrates. In the Galápagos archipelago, a rather young group of volcanic islands, the exchange as well as the opportunity to colonize new substrates and—in evolu‐ tionary terms—to adapt to new micro environments, has been certainly lower than in the

*,* between 0.18 and 0.47, meaning that these yeasts species were found in a maximum

*,* between 0.02 and 0.11, which means that these species were found in

specialization since 70 out of 104 yeasts species analyzed (c.a. 67%) showed a *Si*

)

between 0.92

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227

relationship with the endangered plant species.

and beyond [58].

mediate *Si*

substrates.

showed a very low *Si*

**Figure 5.** Curve of adaptability of the yeasts species studied in Mainland Ecuador and four Islands in the Galápagos Archipelago.

Analyzing this curve it is possible to infer that the higher the slope, the more specialized is the yeast species and vice versa. This kind of modeling is useful to have a general understanding of the behavior of yeast species in the ecosystems. As the information of new collects and characterization of yeasts is updated in the data base of the CLQCA this model will become more robust and accurate.
