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Box 6.1 Light Quality and Germination in Epiphytic Bromeliads (Eva-Maria Voßmann, Stefan Wester, and Gerhard Zotz)

Box 6.1 Light Quality and Germination in Epiphytic Bromeliads (Eva-Maria Voßmann, Stefan Wester, and Gerhard Zotz)

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Germination and Establishment



151



Box 6.1 (continued)

means of four replicates. SD not shown for clarity. The average SD for the

days 5–10 was 8 %, on the remaining days close to zero.)

100



W. sanguinolenta



T. fasciculata



G. lingulata



T. monadelpha



80

60



% germination



6.2



40

20

0

100

80

60

40

20

0

1 2 3 4 5 6 7 8 9



1 2 3 4 5 6 7 8 9



days



These results suggests that light quality does not play a role in determining

the vertical stratification in species occurrence. Moreover, a second run in

complete darkness (6 replicates of 10 seeds per species) indicated that light

was not even necessary to trigger germination in two species. About 50 % of

the seeds of Tillandsia fasciculata and Tillandsia monadelpha germinated in

the dark within 10 days. These seedlings were white, but the extruding

hypocotyl usually turned green very fast once exposed to light. Interestingly,

these results are at odds with data from the only other study on this topic we

are aware of (Pereira et al. 2009). These authors found reduced germination in

two facultatively epiphytic Vriesea species at R:FR ratios <0.2.

The importance of light for the germination process in epiphytic habitats is

thus far from unambiguous. Vasudevan and Van Staden (2010) found that

both germination percentage and growth of rhizoids on developing

protocorms were enhanced by dark pretreatment of the seeds of the orchid,

Ansellia africana, and Rasmussen et al. (2015) supposed that inhibition of

germination by light could assure that seeds sink into organic substrate to

escape desiccation after germination. This is, of course, pure speculation, but

the idea is interesting enough to warrant a closer look at the way light affects

germination in epiphytes.



152



6



Population Biology



Both light quality and quantity can influence germination, and conceivably light

requirements could differ between epiphytes and terrestrial plants. Although many

epiphytic bromeliads (Downs 1964) or ferns (Raghavan 1971) meet this expectation and do not germinate in darkness, there are quite a large number of epiphytic

bromeliads, orchids, or ferns that do not require light for germination (e.g.,

Fernandez et al. 1989; Arditti 1967; Shull 1911, Box 6.1). The hypothesis that

light quality may influence germination in epiphytes similar to terrestrial taxa

(Benzing 1978), thus representing a possible physiological mechanism behind

vertical stratification, is not supported by data either (Box 6.1).

The effects of other important environmental factors, e.g., water availability and

temperature regime, on germination of vascular epiphytes are briefly discussed in

Sect. 5.2. Water availability is not only a major factor for germination success, but

also for early establishment. Not surprisingly, first-year survival is usually strongly

correlated with rainfall in a particular year (Zotz and Schmidt 2006; Zotz

et al. 2005; Olaya-Arenas et al. 2011).

Vivipary, i.e., the germination of seeds before being shed from the parent plant,

is not very common in the plant kingdom with just about 100 known cases

(Elmqvist and Cox 1996), and there is no indication that vivipary is particularly

frequent among epiphytes. However, there are a few reports of vivipary among

epiphytic cacti and bromeliads (e.g., Cota-Sanchez and Abreu 2007; Harshberger

1910). Whereas the observation in Tillandsia tenuifolia (Harshberger 1910) is

enigmatic because there is no obvious advantage of germination in a dry pod, a

fleshy cactus fruit may provide a moist environment for germination under otherwise harsh conditions (Cota-Sanchez and Abreu 2007), and larger viviparous

seedlings may, subsequently, suffer lower mortality than smaller seedlings produced from seeds.



6.3



Growth and Survival



Seedlings and juveniles are the most vulnerable stage in most plants (Silvertown

and Doust 1993). The usually slow growth rates of vascular epiphytes (Sect. 5.5.6)

prompt the expectation of particularly long juvenile phases. Indeed, individual

bromeliads or orchids are on average more than three times older at first reproduction (9.7 Æ 4.5 years, n ¼ 17 species, Table 6.1) than the typical terrestrial herbaceous plant (3.5 Ỉ 3.1 years, n ¼ 63 species, Moles et al. 2004). Twig epiphytes

such as Leochilus labiatus or L. scriptus are enigmatic exceptions to the otherwise

consistent picture of slow maturation in epiphytes (Chase 1986). Possibly the most

stunning testimony of this accelerated life cycle is an observation by James

D. Ackerman (Chase 1986). He found flowering Ionopsis utricularioides

individuals on leaves of Psidium guajava!

Juvenile mortality seems mostly related to drought, as expected from theoretical

considerations. Surface–volume ratios are inevitably larger in smaller plants compared to larger conspecifics, which increases the danger of desiccation, particularly

during drier periods. This size dependence is well documented by two demography



Species

Aspasia principissa

Catopsis sessiliflora

Catopsis sessiliflora

Catopsis sp.

Dimerandra emarginata

Encyclia tampensis

Jacquiniella leucomelana

Jacquiniella teretifolia

Leochilus labiatus

Leochilus scriptus

Lycaste aromatica

Tillandsia deppeana

Tillandsia deppeana

Tillandsia deppeana

Tillandsia deppeana

Tillandsia juncea

Tillandsia juncea

Tillandsia multicaulis



Family

Orchidaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae

Orchidaceae

Orchidaceae

Orchidaceae

Orchidaceae

Orchidaceae

Orchidaceae

Orchidaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae



Years to first

reproduction

10

6

9

9

6

15

6

12

<1

<1

11

11

9

20

[3]

15

18

16

2



4.2



3.3



RGR



Source

Zotz and Schmidt (2006)

Zotz and Laube (2005)

Winkler (2005)

Hietz et al. (2002)

Zotz (1998)

Larson (1992)

Winkler et al. (2009)

Winkler et al. (2009)

Chase (1986)

Chase (1986)

Winkler et al. (2009)

Hietz et al. (2002)

Winkler (2005)

Matos and Rudolph (1984)

Matos and Rudolph (1984)

Winkler et al. (2005)

Hietz et al. (2002)

Winkler et al. (2005)



(continued)



Method

Matrix analysis

Estimates from field observations

Matrix analysis

Estimates from field observations

Estimates from field observations

Estimates from field observations

Matrix analysis

Matrix analysis

Field observations

Field observations

Matrix analysis

Estimates from field observations

Matrix analysis

Field observations

Field observations

Matrix analysis

Estimates from field observations

Matrix analysis



Table 6.1 Time until first reproduction as an important life-history traits of vascular epiphytes. Data come from direct field observations or are estimates

based on matrix model calculations or growth data. Estimates were either taken directly from the sources or calculated from published data. Also given are

estimates for offshoots [in brackets]. Relative growth rates (RGR, in mg gÀ1 dayÀ1) are averages of 65 - 361 plants



6.3

Growth and Survival

153



Species

Tillandsia multicaulis

Tillandsia paucifolia

Tillandsia punctulata

Tillandsia punctulata

Vriesea gigantea

Vriesea gigantea

Werauhia sanguinolenta



Table 6.1 (continued)



Family

Bromeliaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae

Bromeliaceae



Years to first

reproduction

13

8

8

13

7–10

[<5]

13

2.1



RGR

2



Source

Hietz et al. (2002)

Benzing (1981)

Winkler (2005)

Hietz et al. (2002)

Trindade Sampaio et al. (2012)

Trindade Sampaio et al. (2012)

Zotz and Laube (2005)



Method

Estimates from field observations

Estimates from field observations

Matrix analysis

Estimates from field observations

Field observations

Field observations

Matrix analysis



154

6

Population Biology



6.4



Reproduction



155



Table 6.2 Causes of mortality in Vriesea sanguinolenta (in % per size class)

Size class

A1 (atmospherics < 2 cm)

A2 (atmospherics ! 2 cm)

T1 (tanks < 5 cm)

T2 (tanks < 10 cm)

T3 (tanks < 20 cm)

T4 (tanks < 40 cm)

T5 (tanks ! 40 cm)



Causes of death

Drought

Herbivory

51 Ỉ 5

0

42 Ỉ 4

0

30 Ỉ 8

0

32 Ỉ 7

6Ỉ3

20 Ỉ 6

4Ỉ3

0

2Ỉ1

0

0



Substrate failure

17 Ỉ 6

26 Ỉ 9

35 Ỉ 10

39 Ỉ 8

51 Æ 11

45 Æ 12

83 Æ 7



Other/unknown

31 Æ 9

30 Æ 8

35 Æ 9

23 Æ 5

24 Æ 4

51 Æ 11

16 Æ 7



The seven size classes are defined by size and morphology in this heteroblastic species

(A atmospherics, T tank). “Substrate failure” is any disturbance that is related to the host tree,

from flaking bark to tree fall. Data are means Ỉ SE of 7 years. More details in Zotz et al. (2005)



studies in lowland Panama, which lasted for 7 years each (Table 6.2, Zotz and

Schmidt 2006; Zotz et al. 2005). For example, in the orchid Aspasia principissa

both growth and survival correlated with precipitation in smaller size classes, while

larger individuals were completely unaffected. This lack of a response in larger

epiphytes is quite remarkable, because the study period witnessed one of the driest

years (c. 1400 mm aÀ1) on record, and co-occurring trees have been shown to be

strongly affected by such drought (Condit et al. 1995).

Epiphytes root on a living substrate with its own dynamic, and there is substantial evidence that “substrate instability,” e.g., flaking bark, breaking branches, or

even whole tree falls are the major reason for mortality in vascular epiphytes (Hietz

1997; Mondrago´n et al. 2004a; Zotz et al. 2005; Cabral et al. 2015), although

juveniles may primarily die because of desiccation. It would be highly interesting to

combine the demographic data of epiphytes with data on substrate demography.

Unfortunately, this has never been tried. The generally slow development of both

epiphytes and trees could discourage many researchers, but twig epiphytes may

represent an ideal system for “short-term” studies of the race between an epiphyte

to grow and reproduce before its short-lived substrate dies with its client (Cabral

et al. 2015).



6.4



Reproduction



It has been suggested that epiphytes, due to the rather ephemeral nature of their

substrate and their relatively small size, paired with frequently low population

densities, should engage in inbreeding more often than terrestrial perennials

(Bush and Beach 1995; Hooper and Haufler 1997). The available evidence only

partly bears out this expectation. Although the majority of the tested Bromeliaceae

and members of other families such as Gesneriaceae or Melastomataceae are indeed

mostly self-compatible (Bush and Beach 1995; Matallana et al. 2010; Lumer 1980),

the large majority of all studied orchids and ferns are obligate outcrossers. Self-



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6



Population Biology



incompatibility associated with pollinator limitation frequently led to extremely

low fruit set under natural conditions, e.g., only c. 2 % of all flowers develop a fruit

in Tolumnia variegata (Tremblay et al. 2005).

It is still difficult to generalize, however, because our knowledge of the mating

systems in vascular epiphytes is highly biased. Most information is available for

orchids (Tremblay et al. 2005; Ackerman and Montalvo 1990) and bromeliads

(Matallana et al. 2010; Paggi et al. 2013), but only the exceptional study dealt with

the topic in members of other important families, e.g., Araceae (Valerio and

Villalobos 1980), Melastomataceae (Lumer 1980), Gesneriaceae (Bush and

Beach 1995; Marten-Rodriguez et al. 2015), or ferns (Hooper and Haufler 1997).

Ackerman (1986) proposed three pollination strategies for outcrossing

epiphytes, which he believed would ensure successful pollination, but supplied no

quantitative comparisons of the prevalence of these strategies in epiphytic and

terrestrial relatives. Similarly, Tremblay et al. (2005) provide an authoritative

review of the mating systems of orchids, exploring, e.g., latitudinal differences in

fruit set or the evolutionary consequences of small effective population sizes.

Unfortunately, possible differences among epiphytic and terrestrial species were

not addressed. Thus, it is still unresolved, whether a preliminary analysis by

Neiland and Wilcock (1998), who found no differences in fruit set in terrestrial

and epiphytic tropical orchids, is actually valid for this family at large, let alone

other major epiphyte groups such as bromeliads (Paggi et al. 2013). Solid datasets

for a number of different families such as the recent study of Marten-Rodriguez

et al. (2015) with gesneriads are needed to address this question. A fine-scale tuning

of the mating system to environmental gradients within tree canopies is suggested

by the results of a comparative study in Mexico (Hietz et al. 2006). The observed

trend toward higher inbreeding in species colonizing the outer, more dynamic

portion of tree crowns is expected from ecological theory (Grime 1977).

In contrast to Benzing (2000), who assumed self-incompatibility to dominate in

bromeliads, quantitative evidence for 40 species from the Atlantic rainforest

indicates otherwise (Matallana et al. 2010): all 17 epiphytic Tillandsioids were

self-compatible and 12 out of 23 epiphytic Bromelioids. A literature survey

conducted by these authors indicated that the level of self-compatibility in epiphytic

bromeliads is not really distinct from terrestrial species. For example, six of nine

studied terrestrial species shared this character.

Many other aspects of reproduction have also been studied in epiphytes, e.g., the

cost of reproduction (Zotz and Schmidt 2006; Ackerman and Montalvo 1990; see

also Sect. 5.4.4), the specificity of pollinators (Tremblay et al. 2005), or the effect of

spatial population structure on reproductive success (Murren 2002). Results do not

indicate anything genuinely distinctive for epiphytes compared to terrestrial herbs.

This is also true for the possible link of inbreeding and short-term demographic

success of a species, similar to the situation in terrestrial pioneers. Several studies

found a relationship of relative abundance and breeding systems that do not depend

on pollinators. For example, Tillandsia recurvata, a bromeliad accounting for up to

90 % of all epiphyte individuals in a dry forest in Morelos, Mexico, is selfing

(Orozco-Ibarrola et al. 2015), and so are the two orchids Dimerandra emarginata



6.5



Survival on the Ground



157



and Caularthron bilamellatum, which represent almost 60 % of all individual

epiphytes in Annona glabra trees in the moist lowlands of Panama (Laube and

Zotz 2007).

Many epiphytes do not only propagate sexually, but by vegetative means as well.

For one, independent ramets simply result from the partial disintegration of creeping plants (e.g., in many ferns, gesneriads, or cacti), or the breaking apart of

branches of rhizomes of sympodial orchids. Offshoots are another possibility to

secure continuity of a genet, and in many monocarpic bromeliads, the production of

offshoots is an integral part of their life history (Benzing 2000). Additional

offshoots are also known for some orchids, where they form on stems or on flower

stalks. These offshoots are well documented in the horticultural literature, but there

is only one study addressing their importance in the field: Zotz (1999) studied their

occurrence in the orchid, Dimerandra emarginata, in lowland Panama. Their

relatively rare occurrence in 2 % of all individuals and low likelihood of establishment argue against an important ecological role.



6.5



Survival on the Ground



Falling off the substrate (e.g., with pieces of flaking bark) or falling with the

substrate (e.g., in the case of branch or tree falls) are arguably the principal cause

of mortality in larger epiphyte individuals (e.g., Hietz 1997; Mondrago´n

et al. 2004a; Zotz et al. 2005). Three studies have directly tested the implicit

assumption that continued existence on the forest floor is impossible by following

the fate of epiphytes on the forest floor (Mondrago´n and Ticktin 2011; Matelson

et al. 1993; Pett-Ridge and Silver 2002). The results were not entirely consistent:

while most plants died very fast and few plants survived more than a year in two of

the studies, survival on the ground was much higher in the study by Pett-Ridge and

Silver (2002). These differences are certainly partly due to methodology. In contrast to the two other, purely observational studies, Pett-Ridge and Silver (2002)

transplanted plants, which thus had not suffered possible damage during fall.

Moreover, transplants were supported by PVC stakes, thus ensuring tank function,

which would frequently not be the case in naturally fallen individuals. Nevertheless, counting all plants which fall off a branch in a demographic study as dead is

probably an overestimate even for obligate epiphytes. I have repeatedly observed

plants that got caught in and on lower branches, eventually attaching themselves

with new roots and continuing to live there for many years (G. Zotz, unpubl. obs.).

The notion of a “deadly” forest floor must also be qualified for many of the more

flexible members of tree-dwelling flora. Many Peperomias, filmy ferns, etc., will

easily trade bark for, e.g., rock as substrate as long as other abiotic conditions are

conducive to survival. An example from the Fortuna Forest Reserve in Panama also

indicates that at least some epiphytes can be quite opportunistic. Clearing of

montane forest along the road has resulted in a low herbaceous-shrubby vegetation

with little establishment of trees after more than a decade. A substantial number of

epiphytes, e.g., orchids and bromeliads, are found vigorously growing on the



158



6



Population Biology



ground. Similar observations have been made at forest margins or open ecotones

such as the sub-Pa´ramo.



6.6



Comparative Plant Demography



Detailed demographic information is available for about 30 species of epiphytes

(Mondrago´n et al. 2015), equally representing orchids and bromeliads. The dynamics of individual plant populations is summarized by the ratio of the numbers of

individual plants in successive years, the finite rate of population growth (λ). Both

elasticities of vital rates (Franco and Silvertown 2004) and matrix element

elasticities (see Box 6.2, Silvertown et al. 1993) have been used in comparative

plant demography to analyze the relative contributions of different life-history

components (fecundity, survival, growth) to λ, with very consistent results:

Silvertown and Franco distinguished three groups (semelparous perennial herbs,

iteroparous herbs, and woody plants) and discovered that these were usually found

in distinct regions of the parameter space defined by fecundity, survival, and

growth. These analyses included very few epiphytes (e.g., Tolumnia variegata,

Calvo 1993), and not surprisingly, there was no attempt to distinguish epiphytes as a

separate group. A considerable number of demographic studies with epiphytes

published in the last decade now allow such an analysis (Fig. 6.1). With one

exception, a study with Tillandsia makoyana (Martı´nez-Garcı´a 2006), survival

always influenced λ far more than growth (average 75 Ỉ 12 % vs. 21 ặ 10 %,

n ẳ 32 species), let alone fecundity (4 Ỉ 4 %). Thus, these herbaceous vascular

epiphytes resemble long-lived trees in their demography much more than

iteroparous herbs rooted in soil. Noteworthy, there are several, albeit anecdotal,

reports that individual plants in cultivation may reach ages well over 100 years

(Smith 1966; Anonymous 1968).



6.6



Comparative Plant Demography



159



Box 6.2 Population Matrix Analysis of an Epiphytic Orchid



Repeated census data of plant populations allow the construction of life-cycle

graphs and so-called Lefkovitch matrices (for a detailed discussion of the

topic please, refer to Caswell 2001). The figures below show a simplified lifecycle graph and a habit sketch of Dimerandra emarginata. Following the

suggestions of Vandermeer (1978), five stages were recognized in this study

(Zotz 1998 and previously unpublished data): S1–S5, plant size <2 cm,

<5 cm, <10 cm, <18 cm, and !18 cm. Arrows depict possible contributions

of an individual in stage i at time t to stage j at t +1, i.e., after one 1 year, either

due to growth (P) or due to the production of progeny (F). Since only

plants > 5 cm reproduce and a seedbank is lacking, additions to S1 come

only from S3–S5.

F5

F4

F3

S1



P1



S2



P2



S3



P3



S4



P4



S5



S5



S1



The average data of three annual censuses (1993–1996) were used to produce

a projection matrix (Table 1, B ¼ {bij}, where i, j ¼ 1, 2, 3, 4), which contains

the transition probabilities and contributions (i.e., fecundity) of an average

individual at different stages of the life cycle over a unit time interval, and

operates over a vector (nt) containing the distribution of individuals in the

population.

The size of the entire population after one time interval is equal to the

product of matrix B by vector nt or

(continued)



160



6



Box 6.2 (continued)



Population Biology



N tỵ1 ẳ B nt :



The largest eigenvalue of this matrix (Table 1 below) is equivalent to the

finite rate of increase of this population (λ), 0.99 in the shown example; i.e.,

the population is stable. Further analyses, e.g., an elasticity analysis (Table 2

below), allow the quantification of different demographic processes to λ. We

distinguish (compare Silvertown and Doust 1993): stasis and retrogression

(L, remaining in the same or lower stage class), growth (G, change into a

higher one), or reproduction (F, recruitment of seedlings from current sexual

reproduction). This approach quantifies the proportional change in λ resulting

from an infinitesimal proportional change in a matrix transition aij. Importantly, elasticities of transitions of similar type can be added, and all

elasticities of a transition matrix sum up to unity. This allows the comparison

of the relative importance of different types of transitions between

populations of the same species or among species (see Fig. 6.1). In the

shown example L alone accounts for 73 %, while F is a mere 3 %.

Table 1 Average transition probability matrix for Dimerandra emarginata in the Barro

Colorado National Monument

Stage at year t

Stage at year

t+1

S1 (<2 cm)

S2 (<5 cm)

S3 (<10 cm)

S4 (<18 cm)

S5 (!18 cm)

Mortality

rate



S1

0.37 Ỉ 0.12

0.25 Æ 0.09

0.03 Æ 0.01



S2

0.01 Æ 0.01

0.50 Æ 0.05

0.36 Æ 0.12

0.04 Æ 0.02



0.35



0.04



S3

0.05 Æ 0.01

0.07 Æ 0.01

0.54 Æ 0.06

0.32 Æ 0.10

0.03 Æ 0.04

0.05



S4

0.04 Æ 0.03

0.02 Æ 0.02

0.16 Æ 0.02

0.61 Æ 0.01

0.17 Æ 0.01

0.04



S5

0.27 Æ 0.18

0.02 Æ 0.02

0.23 Æ 0.06

0.70 Æ 0.10

0.06



The previously unpublished data are averages ỈSD of three annual matrices. For more

details, see Zotz (1998)



Table 2 Average elasticity matrix for Dimerandra emarginata in the Barro Colorado

National Monument

Stage at year t + 1

S1 (<2 cm)

S2 (<5 cm)

S3 (<10 cm)

S4 (<18 cm)

S5 (!18 cm)



Stage at year t

S1

S2

0.02

0

0.03

0.05

0

0.04

0

0

0

0



S3

0

0.01

0.12

0.08

0.01



S4

0.01

0.01

0.05

0.22

0.07



S5

0.02

0

0.

0.05

0.20



The previously unpublished data are averages of three annual matrices. Different styles

indicate stasis and retrogression (L, remaining in the same or lower stage class: normal),

growth (change into a higher one, bold), or reproduction (recruitment of seedlings from

current sexual reproduction, italics)



1

2 0

30 0

4

5 0

60 0

7

8 0

90 0



Gr

ow

th



90

80

70

60

50

40

30

20

10



10

20

30

40

50

60

70

80

90



10

20

30

40

50

60

70

80

90



Fecundity



b



l

va

rvi

Su



l

va

rvi

Su



90

80

70

60

50

40

30

20

10



Gr

ow

th



a



161



10



Metapopulations



2

3 0

40 0

5

6 0

70 0

8

90 0



6.7



Fecundity



Fig 6.1 Comparison of the distribution of 32 epiphyte species (open circles) in the growth–

survival–fecundity space with a) terrestrial herbaceous perennials and b) trees (closed circles).

Studies with epiphytes were taken from the compilation of Mondrago´n et al. (2015) with additional

data for Dimerandra emarginata (Zotz 1998), Tillandsia multicaulis and T. punctulata (ToledoAceves et al. 2014), and Pachyphyllum hispidulum (Zotz et al. 2014). Data of terrestrial plants are

from Silvertown et al. (1993). When more than one transition matrix was available for a given

species, averages were used



In analogy to these interspecific analyses, life-history components should also

differ between populations of the same species (Franco and Silvertown 2004), but

there are few such studies with epiphytes. For example, Zotz (2005) studied three

populations of the epiphytic bromeliad, Vriesea sanguinolenta, along a precipitation gradient across the Isthmus of Panama. The results hardly met expectations.

Although population growth rates increased with precipitation, mortality rates

being highest at the dry end and growth being highest at the wet end, the differences

in the importance of the three demographic processes growth, survival, and reproduction for population growth were rather small.

As emphasized by Mondrago´n (2011), such demographic studies do not only

answer basic scientific questions, but provide important information for management plans in conservation. Particularly in those regions, in which plants are

collected in large numbers (Chap. 10) as non-timber forest products with an obvious

economic importance, such management plans are essential for a sustainable use.

First suggestions for such long-term management are now available (Mondrago´n

and Ticktin 2011; Wolf 2010).



6.7



Metapopulations



Metapopulations are populations of populations which are interconnected by seed

dispersal, and metapopulation models focus on the importance of colonization and

extinction processes for regional dynamics rather than local processes (Hanski and

Gaggiotti 2004). Overton (1994) was the first to apply the concept of metapopulations to plants anchored on trees. Although he studied parasitic mistletoes,

these are comparable to true epiphytes in this regard because both groups are



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