Monarch butterflies in southern SpainPatch dynamics and persistence

During the ninetieth century the Monarch butterfly spread across the PacificOcean. At the same time, migrants crossing the Atlantic Ocean were seen for thefirst time in several European countries (Fig. 1). Breeding populations onlyestablished in the islands. During the 1980s some small breeding colonies werefound along the coast of Spain. However, these were ephemeral.

J. Fernández Haeger1, D. Jordano2 & M. Zalucki3

1,2. University of Córdoba, Spain.3. University of Queensland. Brisbane, Australia.

1. bv1fehaj@uco.es 2. bv1jobad@uco.es 3. m.zalucki@uq.edu.au

Since 1997 we have regularly recorded monarch butterflies along thesouthernmost coastal area in Europe (36o N). Part of this area is within theAlcornocales Natural Park and also the Natural Park of the Gibraltar straits.

OBJECTIVES

The aim of the study was to inventory suitable breeding habitats for the monarchbutterfly and to assess its status in the study area.

METHODS

Starting in June 2008, we systematically surveyed a coastal area of 900 km2 closeto the Gibraltar strait (Fig. 2). We located 62 milkweed patches, which were visitedon a regular basis over 30 months. We searched for adults, eggs, larvae andpupae, thus determining whether the patch was occupied or empty.

RESULTS

Fig. 2 Distribution of the 62 host plant patches in the study area. Gomphocarpusfruticosus is more abundant and widespread than Asclepias curassavica; G.physocarpus is scarce and restricted to just 2 patches.

Table 1 Butterflies and immature stages recorded during 1945 visits to patches.

HOST PLANT

STAGE A. curassavica G. fruticosus TOTAL

No. EGGS 2964 815 3779

No. LARVAE 2294 2005 4299

No. PUPAE 378 250 628

No. BUTTERFLIES 3095

Maximum patch occupation rangedfrom 50 to 65 % among years (Fig. 6).

0

10

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40

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60

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80

90

100M

on

thly

Occ

up

ancy

(%

)

Patches

PatchesOccupied: 47Unnocupied: 15

5 10 15 20 25 30 35 40 45 50 55 6260

0

10

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30

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50

60

70

2008 2009 2010 2011

No

. of

Pat

che

s

Year

Vacant Occupied

0102030405060708090

100

3 4 1 2 3 4 1 2 3 4

2008 2009 2010

Pat

ch O

ccu

pan

cy (

%)

Quarter & Year

Fig. 8. Variation of patch occupation among years

0

100

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600

700

6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 12

2008 2009 2010 2011 2012

No

. o

f In

div

idu

als

Month and Year

Monarch butterflies

Inmature stages

2523

In the study area the Monarch is multivoltine with no diapause, breedingthroughout the year. We recorded immature stages in 65.5 % of field-workdays, even during winter. In the last five years there were two major populationoutbreaks, leading to severe patch defoliation (Fig. 4, see pictures at the top).

Fig. 1. Early citations of Monarch butterflies in European countries.

Patch occupation also showed strongseasonal variation, peaking in late summerand early autumn (Fig. 7)

CONCLUSIONS

There were huge differences in butterfly and immature abundance among patches and amongmonths and years. While a few patches make a large contribution to the population, othersseem to be sinks. Good patches are located next to permanent streams in riparianhabitat, where microclimate and shelter from the strong easterly wind provide more suitableconditions during the summer drought.

The monarch population persists at the regional scale, but local extinctions and recolonizationswere frequent events. Local extinctions were mainly driven by flooding, severe host plantdamage by frost, complete patch defoliation by caterpillars (see pictures at the top), diversion ofthe water supply and vegetation clearings.

Spain

The presence of butterflies and/or immatures in each patch was not constant.Only 4 patches were occupied over ninety percent of months (Fig. 5).

Fig. 3 Patch occupation by monarchs butterflies. Occupied patches were thosewhere the species was recorded at least once during the 2008-2011 period.