Hunting and Feeding: Box Jellyfish (Chironex fleckeri)

The notorious box jellyfish, Chironex fleckeri, is not only among the world’s most dangerous venomous creatures, it is also a very active and formidable predator (Alderslade et al, 1998). The box jellyfish uses the venom in its tentacles not just as a defence mechanism, but also for the express purpose of incapacitating and eating its prey (Marsh and Slack-Smith, 2010). Equipped with as many as 15 tentacles, lined with thousands of stinging cells and armed with over 5,000 specialized barbed nematocysts per arm, the sting from a box jellyfish has the ability to pierce flesh, crustacean cuticle and even the shells of molluscs (Uhlenbroek, 2008). Each cell contains a filament lined with barbs that, when triggered by contact with prey, release explosively and instantly stun and paralyse the target (Marsh and Slack-Smith, 2010). The rapid ejection of this barb is one of the fastest cellular processes ever recorded in nature and turns the barbed filaments inside out with roughly the same energy as firing a small-calibre bullet (Uhlenbroek, 2008).

Belonging to the class Cubozoa, box jellyfish are not true jellyfish but are closely related (Marsh and Slack-Smith, 2010). They are capable of moving at speeds up to 7.2kph by using a form of jet propulsion and are equipped with 24 eyes arranged in four groups of six on each side of the body (Marsh and Slack-Smith, 2010). While most of these eyes are simple organs capable of responding only to light and dark, one pair in each cluster has the ability to form images and may guide the jellyfish to its prey (Uhlenbroek, 2008).

Whilst the box jellyfish usually preys on small fish and crustaceans, they pose a significant threat to humans with its excruciatingly painful stings causing heart failure and shock often leading to drowning (Uhlenbroek, 2008).

Reference:

Alderslade, P., Bloom, D.A. & Burnett, J.W. (1998). Partial purification of box jellyfish (Chironex fleckeri) nematocyst venom isolated at the beachside. Toxicon, 36(8), 1075-1085.

Marsh, L.M. & Slack-Smith, S. (2010). Field Guide to Sea Stingers and Other Venomous and Poisonous Marine Invertebrates. Western Australia, AUS: Western Australian Museum.

Uhlenbroek, C. (2008). Animal Life. Penguin Group, UK.

Hunting and Feeding: Red Crossbill (Loxia curvirostra)

The red, or common, crossbill is a species of finch whose diet consists almost exclusively on the seeds of coniferous trees (Hahn, 1998). As such they have adapted a distinctive trait that enables them to deal with their specific diet. The unusual crossed bill of these birds allows them to prise open the tough cones of conifers before they ripen and open naturally (Uhlenbroek, 2008, pg 191). Their adapted bill comprises of an elongated upper bill and a shorter, crossed lower bill, which – while common to all crossbill species – can differ in size and shape between species and populations within a species according to their preferred type of cone, be it spruce, pine or larch (Marquiss, 2002).

In order to feed, the crossbill simply inserts its closed bill into a cone and opens the crossed tips, thereby prising open the scale of the cone and allowing the bird to eat the seed inside (Marquiss, 2002). Because of their highly resinous diet, these birds must frequently visit water sources in order to drink and clean off their bills (Uhlenbroek, 2008, pg 191).

The adaptation of this bill gives an advantage over other finches inhabiting the same area due to the ability of the common crossbill to breed whenever the cone crop ripens, even during the winter months (Hahn, 1998).

References:

Hahn, T.P. (1998). Reproductive seasonality in an opportunistic breeder, The Red Crossbill, Loxia curvirostra. Ecological Society of America, 79(7), 2365-2375.

Marquiss, M. & Rae, R. (2002). Ecological differentiation in relation to bill size amongst sympatric, genetically undifferentiated crossbills Loxia spp. International Journal of Avian Science, 144(3), 494-508.

Uhlenbroek, C. (2008). Animal Life. Penguin Group, UK.

Hunting and Feeding

Feeding is fundamental in providing plants and animals with the energy required to undertake various chemical processes within their bodies that are essential for life (Uhlenbroek, 2008, pg 179). There is a wide variety between animals in regards to the food they eat and how it is obtained; from carnivorous bears to herbivorous deer. To achieve this, a range of adaptations have evolved.

Animals are generally classified according to their diet; carnivores eat other animals and so have developed specialized detection methods and behaviours such as stalking, ambushing and co-operating with one another to bring down larger prey (Uhlenbroek, 2008, pg 179).

Herbivorous diets consist of plants and as such they have also formed specialized behaviours that allow them to feed. The evolution of grinding teeth – such as in elephants – allow them to chew tough plants and unique inner organs such as the appendix in koalas allow a diet of entirely eucalyptus leaves (Bollinger et al, 2009).

Omnivores and scavengers feed on a wide variety of food including plants, animals and decaying matter (Clark, 1982). Consequently, they often lack any highly specialized adaptation but instead require the flexibility to utilise such a wide range of food (Uhlenbroek, 2008, pg 179).

These different types of feeding behaviours and adaptations allow for the development of food webs within ecosystems.

References:

Clark, D.A. (1982). Foraging Behavior of a Vertebrate Omnivore (Rattus Rattus): Meal Structure, Sampling, and Diet Breadth. ESA Ecology, 63(3), 763-772.

Bollinger, R.R., Everett, M.L., Fisher, R.E., Parker, W., Smith, H.F.& Thomas, A.D. (2009). Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix. Journal of Evolutionary Biology, 22(10), 1984-1999.

Uhlenbroek, C. (2008). Animal Life. Penguin Group, UK.