Predation Flashcards
What is predation?
Predation occurs when members of one species eat those of another species.
Involves the killing of prey or partial predation, and includes herbivory, carnivory, insect parasitoids, parasitism and cannibalism.
predators and prey on the rocky shore
- Predators tend not to be as fast or mobile as terrestrial counterparts
- Prey adopt a ‘fortress’ strategy to overcome attack (shell, stinging cells, spines)
- Predators are therefore adapted to break down these defenses
dog whleks overcoming fortress strategy
• Some of the commonest predators on the shore – great examples of overcoming ‘fortress’ strategies
• Injects a narcotic and digestive enzymes through bored hole m
Feeding is not rapid – can take 24-60 hours to drill, and sometimes days to consume the flesh, depending on prey
Predator Size, Prey Size, and the Scaling of Vulnerability: Hatchling Gastropods vs. Barnacles (compulsory reading)
A. Richard Palmer 1990,
Examines the size—dependence of prey vulnerability using replicate groups of hatchling Nucella emarginata, held in cages in the laboratory with five size categories of barnacles (Balanus glandula and Chthamalus dalli). Measuring the diameters of both successful drill holes and unsuccessful drill attempts. For three size classes of hatchling (<3.5 mm), the vulnerability of barnacles (percent successful attacks) decreased roughly sigmoidally with increasing barnacle size.
Surprisingly, even the smallest hatchlings were able to consume at least a few of (<10%) the largest barnacles offered, no discrete upper size limit of prey was observed.
Over time of feeding on the same prey the dog whelk will learn how to feed suturally. sutural attacks are where the siphon is pressed between the scutal plates rather than through the plates, these attacks were advantageous as they were much faster, however, were most consistently successful only for larger barnacle.
Predators - crabs
Crabs, Carcinus maenas
• Broad diet, but in Europe they specialise in eating mussels, littorinidae and dog whelks • Distribution of prey items varies, if they are in a group there is more option for selectivity than on their own. Use their chelae to smash or chip shells depending on size & thickness. Littorinidae can be pulled out without breaking the shell. Sheltered shore littorinids have thicker bigger shells, and can resist this better.
Predator - nudibranchs
Nudibranchs
• Often specialise from birth on one prey type. ○ Aeolidia papillosa have a pair of jaws and have reduced radular teeth to one per row forming a comb-like structure for raking in food. This allows them to take a chunk out of Actinia equina and rasp away at the chunk. The compromise of being so specialised is that you rely directly on the population of another species.
Predators - predatory fishers.
• Residents, partial residents, tidal and seasonal visitors (different dynamic due to their variability)
• Most are large enough to overcome fortress strategy by eating prey whole
• Lipophrys pholis – wide-ranging diet, algae, amphipods but mainly barnacles and winkles
Separation between adults and juveniles, juveniles only eat cirri and adults eat entire barnacle
what is the optimal foraging theory?
- A theory from the 1970’s, which was accepted for a long time and basically says: any organism, any predator will feed in such a way it will maximise its energy reserves.
- Now largely not accepted, as it makes important assumptions about what an organisms knows about its environment. Is still the aim for all organisms.
Compulsoy reading; Effect of disturbance on foraging: whelk
Rilov et al (2005). Effect of disturbance on foraging: whelk activity on wave-exposed rocky shores with minimal tidal range. Marine Biology, 147(2), 421-428. Read abstract.
• Stramonita hameastoma (big whelks) – were found in very low abundance in an area restricted by waves for 85% of the time despite high prey abundance. Prey are there as the waves offer protection from the whelks. • Feeding choice also affected - high wave action = no preference and more favourable conditions = more selectivity by avoiding small prey to maximise intake Subsequent feeding and foraging is then governed by fullness of gut – below threshold = forage; above = remain in shelter
• Predators have an overall feeding strategy related to energy budget; this has been considered in detail for Carcinus maenas
Maximise energy obtained from prey – attack the size of prey that yields the greatest amount of energy allowing for energy spent by the predator (Hughes and Elner, 1979)
What are crabs approch to mussels?
- Manipulates (grabs hol of it) for 1-2 seconds; accept or reject item
- Attempt to crush shell – single squeeze to breaking along edge
- Time taken increases with mussel size
- Prey-choice experiments indicate that the time spent breaking shell and eating mussel increases with increasing mussel size. As mussel size increases prey value increases to a maximum (optimum size)
- Larger crab eats mussels smaller than optimal as the crabs come from a setting with more threats, as they are acting in a way that increases the speed of foraging, whilst they are exposed to predation. This is where the optimal foraging theory begins to fall apart.
- Smaller crabs, are however, eating optimally.
• Predators have an overall feeding strategy related to energy budget; this has been considered in detail for Carcinus maenas
Maximise energy obtained from prey – attack the size of prey that yields the greatest amount of energy allowing for energy spent by the predator (Hughes and Elner, 1979)
What are crabs approch to dogwhelks and littorinids?
• All dogwhelks are attacked, as they are not clumped in the same way as mussels are
• Discarded if not broken in 0.25-2.75 minutes
• Small shells are easily crushed
• Large shells opened by breaking apex (snap the top of) or columella (exposed sites)
Chipping lip of shell (crack the bottom of) – economical on sub-optimum snails
Give a predation controll on morphology
• Predation can interact with physical factors to affect the population structure and even the morphology of prey species - the dogwhelk Nucella lapillus shape varies greatly from wide and thin-shelled on exposed shores to narrow, thick-shelled on sheltered shores
Aperture ‘teeth’ thicken the lip and provide added protection against predators – occurs as growth stops and shell lip thickens
• Growth of ‘teeth’ and shell can vary in response to presence of predators Palmer (1990b) Hydrobiologia 193, 155-182 ○ 3 treatments; clean seawater, seawater flowing past Cancer fed on fish and seawater flowing past Cancer fed on Nucella ○ All whelks formed some apertural teeth over 3 months ○ Largest teeth produced by those in treatment 3 (presents of damaged contraspecifics) – but showed no growth (antipredatory response; more safe being smaller so they could hide further back in their shell.
WIDER READING: relationship between sea star and a mussel.
Paine, R. (1974). Intertidal community structure. Experimental studies on the relationship between a dominant competitor and its principal predator.Oecologia,15(2), 93-12O.
• Paper looks into the interaction of predator and prey (Pisaster ochraceus and Mytilus californianus, respectively) and how this influences the abundance and distribution of the 2, as well as coexisting species. • Experiment involved removal of the main predatory carnivore Pisaster • The control site showed that abundance of Pisaster and its immigration rates into the site had strong seasonality, suggesting the influence should be greatest in summer and autumn • Control areas showed no zonation changes but once the predator was removed in the experimental zone there was a 0.67m vertical extension in the distribution of M. californiacus after the first year (this slowed in the following yrs); Pisaster was returned and ~20cm of mussels were consumed within the first 3yrs, causing the lower band to move back towards its original position Paine argues that the lower limits show ‘biological organisation’ and finds it difficult to believe otherwise; the fact that they both occupy such specific niches is representative of the diversity of the rocky shore (it allows other species to occupy equally specific biological niches)
WIDER READING: 2 predator prey interactions.
Scyphers, S.B. & Powers, S.P., 2013. Context-dependent effects of a marine ecosystem engineer on predator-prey interactions.Marine Ecology Progress Series, 491, pp.295–301.
· Studied 2 interactions: Atlantic croaker Micropogonias undulatus predation on grass shrimp Palaemonetes pugio and blue crab Callinectes sapidus predation on brown shrimp Farfantepenaeus aztecus · Grass shrimp survival was higher in oyster reef habitats, as oppose to those without structures, supporting the idea that habitats with more complex structures can provide refuge for species lower down the food web o This benefit to the shrimp was found to outweigh the effects of light on the visual predator foraging efficiency. · Prey survival as affected by light level and habitat context showed a more complex relationship in the Blue crab-brown shrimp interaction o Low light and structureless = low survival, probably because the multi-sensory predators are better adapted to these conditions and so there’s an element of surprise to their attack o Higher light conditions = higher prey survival, implying that prey avoidance is more efficient under these conditions o Prey survival was consistent in habitats with more complex structures, implying that this is a more important factor in predator avoidance, providing refuge across a spectrum of light intensities. Note: This experiment was a mesocosm so caution must be taken when interpreting the results, as it was conducted under controlled conditions, albeit in an outdoor environment.
To explore how the multiple influences of an ecosystem engineer affect trophic interactions, we conducted mesocosm experiments with common estuarine species (i.e. Atlantic croaker and grass shrimp, and blue crab and brown shrimp) to test the effects of habitat context (high complexity oyster reefs vs. structureless bottom) and light level on prey survival. Atlantic croaker Micropogonias undulatus predation on grass shrimp Palaemonetes pugio was significantly reduced by the presence of oyster reef structure and was not affected by light level. In contrast, blue crab Callinectes sapidus predation on brown shrimp Farfantepenaeus aztecus was influenced by the interaction of habitat context and light level: the presence of oyster reefs reduced brown shrimp survival rates at high light levels, but increased survival in low light.
Polymorphism
We see polymorphism because in any given environment there are a number of sub niches, within niche’s which are filled by the different polymorphs.
• Colour morphs provide protection under different circumstances. The substrate they are on changes when the tide changes. Yellow (citrina) morphs stands out in reflected light but is camouflaged by transmitted light – reverse for the dark reticulata morph
