Thursday, April 26, 2012

The Joys of the Cowslip

Cowslip, Primula veris
What a joy to behold the Cowslip! Its long stalk seems almost too long, a bare stick of a thing rising from a rosette of verdant leaves to support a splash of yellow-orange flowers. These can number up to 30 on some plants (1), and such a number on such a single stalk would look ridiculous were it for their delicate hue and wonderful bell shape.
With its preference for unimproved grassland, Cowslips (Primula veris) have seen a decline in number throughout Europe in the last number of years. This decline can be attributed to changes in land-use practices (2), such as:
  • the loss of traditional hay-meadow management
  • the loss of grazing
  • an increase in ploughing
  • ongoing destruction and nutrient enrichment of permanent grassland.
And while this decline is a pity from our, aesthetic point of view, it is a potential disastrous development for P. veris. Spillmann et al. have shown that reproduction in small populations of P. veris is strongly reduced, with problems such as in breeding depression being observed in those small populations that do reproduce (3). In the short term, reduced reproduction poses a risk of extinction to small populations of P. veris. Small populations will also be less likely to respond to environmental changes, which increases their long term risk of extinction.
Cowslip (Primula veris) flowers
 It is not all bad news however, as the decline in number of P. veris in the UK has been less than that of other countries. This is due to the incorporation of its seeds in wildflower seed-mixtures that are sown on new or upgraded road and motorway verges, embankments and urban conservation areas (2). Such policies could be used by other countries, Ireland included, to maintain this magnificent flower for the future.

  1. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 226
  2. Brys  and Jacquemyn, 2009. Journal of Ecology 97 pp. 581-600
  3. Spillmann et al., 2000. Journal of Ecology 88 pp. 17-30

Tuesday, April 24, 2012

The Holly and the Ivy.... and the Holly Blue

Holly Blue Butterfly, Celastrina argiolus
The Holly Blue butterfly (Celastrina argiolus) is on the wing at this time of the year, its delicate blue colour gracing holly trees where females will lay their eggs. This activity explains their common name, Holly Blue, but is something of a misnomer. C. argiolus is a polyphagous insect, one of the only true polyphagous butterflies in Britain and Ireland (1), and in North America (where it is called the Spring Azure) it is associated with an entirely different set of plants (2). At this time of the year, holly is certainly its preferred choice in this part of the world. It will however produce a second brood from August to September and it then will lay its eggs on ivy plants (3). The popularity of both these host plants in urban habitats has lead to C. argiolus adapting well to city environments (1).

Holly Blue Butterfly, Celastrina argiolus
  1. Dennis, 2010. A Resource Based Habitat View for Conservation: Butterflies in the British Landscape pp. 23, 231
  2. Pyle, 2007. Sky time in Gray's River: living for keeps in a forgotten place p. 112
  3. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 108

Saturday, April 21, 2012

Woodrush Seed Dispersed by Ants

Field Woodrush, Luzula campestris
Seed dispersal in plants is very important for avoiding sibling competition, reducing seed/seedling mortality by predators or pathogens and colonisation of new sites (1). As a low growing, often hidden grass, the Field Woodrush (Luzula campestris) lacks the height to disperse its seed successfully over a large distance. So it ingeniously employs the services of ants to aid it, a relationship known as myrmecochory. The seeds are covered with an eliasome, an external appendage that is rich in lipids, amino acid, or other nutrients. Ants collect the seeds, transfer them to their colony and feed the eliasomes to their larvae (2). While this succeeds in decreasing competition and aids in the colonising of new sites it also provides the perfect environment for developing seedlings. Ant nests are significantly richer in some essential plant macronutrients than their surrounding environments, such as phosphate, potassium and nitrate (2).

  1. Traveset and Rodríguez-Pérez, 2008. Encyclopedia of Ecology pp. 3188-3194
  2. Oostermeijer, 1989. Oecologia 78 pp. 302-311

Two-Banded Longhorn Threat to Pine Plantations?

Two-Banded Longhorn Beetle, Rhagium bifasciatum
The most attractive family of beetles present in Ireland are easily the longhorn beetles (family Cerambycidae). With their distinctive antennae that are always at least two thirds as long as the body large size and often brightly coloured bodies longhorns should be quite conspicuous. However they are often difficult to find, mainly due to their life history. Larvae are found deep inside wood which they eat with their powerful jaws, often burrowing so deep into trees that adults have been known to emerge from furniture made from attacked timber (1). The adults of many species do not feed at all, but those that do feed on flower nectaries and a variety of plant material.
Two-Banded Longhorn Beetle, Rhagium bifasciatum
Of the 22 species of longhorn present in Ireland (2), one of the most common is the Two-banded Longhorn Beetle (Rhagium bifasciatum). While its antennae are not as impressively large as some of its relatives, it is nonetheless an attractive beetle sporting chestnut elytra that each show two slanted yellow bands. Economically, it has no direct effect on forestry activity as, although the adults do feed on conifer leaves, the larvae attack decaying softwood (3). However R. bifasciatum could be a possible vector for the pine wilt nematode Bursaphelenchus xylophilus (4), the causative agent of pine wilt, a disease that can kill established pine trees in weeks (5). Ireland currently does not have a problem with the pine wilt nematode, however strict quarantine must be used to avoid infection of R. bifasciatum in this country.

  1. McGavin, 2005. Pocket Nature Insects and Spiders pp. 112-113
  2. Anderson at al., 1997. Irish Coleoptera.  A revised and annotated list.  Irish Naturalists’ Journal Special Entomological Supplement
  3. Desch, 1973. Timber; its Structure and Properties p. 270
  4. Robertson et al, 2008. Pine Wilt Disease: A Worldwide Threat to Forest Ecosystems Part IV pp. 221-234
  5. Mota et al., 2008. Pine Wilt Disease: A Worldwide Threat to Forest Ecosystems

The Cuckoo Flower

Cuckoo Flower, Cardamine pratensis
As May approaches, so the Cuckoo Flower (Cardamine pratensis) blossoms. This perennial of damp grassland and stream sides has the most wonderful blush-purple flowers atop a stem rising at most 55 cm from a basal rosette of leaves (1). C. pratensis is actually a species complex, comprising a group of species with marked karyological and morphological variation that cover its large range, from Asia, Europe, North Africa and North America (2).Being a plant often present in grazing areas, C. pratensis has the ability to regenerate readily from any damage caused. Adventitious buds on the leaves result in the creation of a 'bud bank' in areas (3). A bud bank is an accumulation of dormant buds in the soil which serves to as a source of plant asexual regeneration after disturbance. When used in concert with seed banks, bud banks of C. pratensis allow the survival and proliferation of populations of the plant.

  1. Phillips, 1977. Wild Flowers of Britain p. 18
  2. Lihovál et al., 2003. Taxon 52 pp. 783-801
  3. Klimešová and Klimš, 2007. Perspectives in Plant Ecology, Evolution and Systematics 8 pp. 115–129

Friday, April 20, 2012

The Problems with the Decline of the Bumble-Bee

Queen Red-Tailed Bumble-Bee, Bombus lapidarius
The decline in bee numbers in Europe over the past 60 years has been a source of concern for a number of reasons. As well as the obvious loss of biodiversity, there is also the problem of a decrease in associated wild plant species and a decrease in the yield of certain crops (1). Bumble bees are no exception to this decline. In Ireland, six of the twenty species recorded are classed as being endangered or vulnerable (2).

Irish Bumble-Bee Species and Their Conservation Status*+
Species Status
Bombus distinguendus EN
Bombus ruderarius VU
Bombus sylvarum EN
Bombus monticola LC
Bombus lucorum LC
Bombus magnus DD
Bombus cryptarum DD
Bombus terrestris LC
Bombus pratorum LC
Bombus hortorum LC
Bombus jonellus LC
Bombus pascuorum LC
Bombus muscorum NT
Bombus lapidarius NT
Bombus barbutellus EN
Bombus rupertris EN
Bombus campestris VU
Bombus bohemicus NT
Bombus vestalis NE

One of the possible reasons often cited for this decline is the strict dietary specialisation of certain species (3). Those species who rely on a smaller number of plant species for food should be more threatened. However, this hypothesis is not borne out in the case of the Red-Tailed Bumble Bee (Bombus lapidarius). In Britain, it is a ubiquitous species, yet it has a very narrow floral diet (4), which dismisses the idea that diet alone is the cause of declining bee numbers.
Queen Red-Tailed Bumble-Bee (Bombus lapidarius)
With its red-orange rump and jet black body, B. lapidarius is quite the attractive species. Females can be seen at this time of year looking for burrows under stones in which to build nests (5,6). Unfortunately, B. lapidarius is classed as near treathened in Ireland (2). This decline has come in parallel with a loss of its major habitats here, coastal dunes and unimproved grassland. However as the example above with regards to diet shows, the decline is most likely due to a combination of factors.

*Conservation Status Key: EN=Endangered; VU=Vulnerable; NT=Near Threatened; LC=Least concern; NE=Not evaluated; DD=Data deficient.
+Adapted from Fitzpatrick et al., 2007.

  1. Goulson et al., 2008. Annual Review of Entomology 53 pp. 191-208
  2. Fitzpatrick et al., 2007. Conservation Biology 21 pp. 1324-1332
  3. Goulson et al, 2009. Biodiversity and Conservation 17 pp. 3269-3288
  4. Connop et al., 2010.  Biological Conservation 143 pp. 2739-2746
  5. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 144
  6. Chinery, 1997. Collins Gen Insects p. 250

The Stress of Being a Sparrow

One of the most commonly encountered birds in both town and country is the House Sparrow (Passer domesticus). They are particularly active at this time of year, its mating season (February to May), when individuals and small groups can be seen collecting nesting materials and feeding. Remarkably, P. domesticus has altered its ecology to live in close association with humans. This is thought to have occurred with the development of the first towns and cities, when animals such as horses filled the streets with their seed-rich droppings (1). Such adaptability has given it a vest range, covering most of Africa and Eurasia. Introduction to North America took place in the 1850s on the East Coast of the US: colonisation was so intense that it took only 50 years for P. domesticus to reach the Pacific coast (1). Due to its affinity for human habitation however, it tends to be only locally common in areas (2). The drab looking females contrast with the well marked males, who show contrasting grey, chestnut and black colours.
Male House Sparrow, Passer domesticus
As social birds, flocks of P. domesticus are subject to strict hierarchies, and it has been found that these hierarchies are maintained by the physiological state of the bird, namely their size (3). Birds of a large size tend towards dominant positions within the hierarchies, with smaller birds being subordinates. When these positions were altered experimentally, with smaller birds being installed as dominants and vice versa, it was found that both groups suffered increased stress (measured as corticosterone concentrations, energy expenditure and immune functions) as a result of their new positions (4). When the birds were then given a choice of social position they reverted to type, with smaller birds opting for subordinate positions and larger ones for dominance.

  1. Beletsky, 2006. Collins Birds of the World pp. 404-406
  2. Sterry, 2009. Collins Complete Guide to Irish Wildlife p. 90
  3. Goymann and Wingfield, 2004.  Animal Behaviour 67 pp. 591– 602.
  4. Lindström et al., 2005. Hormones and Behavior 48 pp. 311 – 320