Light Pollution And Nocturnal Animals Biology Essay


As the advancement in technology has been achieved by human, the usage of artificial lightning has increased dramatically which induced a global problem: light pollution. It is an effect of outdoor lightning includes sky glow, light trespass and glare. Sky glow is the brightening of sky due to natural and human made factor. Light trespass is unwanted light is being emitted such as streetlights (Teikari 2007). Light pollution can be categorized into astronomical light pollution and ecological light pollution. Verheijen (1985) proposed photo-pollution as light pollution which associates with negative effect on wildlife. It is mainly due to sky glow, lighted buildings, billboards, video advertisement, and vehicles which can disrupt ecosystems (Beier 2006). Light pollution occurs by alteration of nighttime light levels by artificial illumination which occurred worldwide due to rapid expanding form and extensive human development on areas (Bird et al 2004). Artificial lightning has increased proportionately with the increase rate of human population growth. Recent research has indicate that almost 20% of the Earth surface has been subjected to light pollution (Cinzano et al 2001). In this essay, we focus our topic on the relationship and the effects between ecological light pollution and nocturnal animal.

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Increasing in light intensity in light pollution will disrupts the circadian clock that generates endogenous rhythms in physiologic and behavioral effects (Turek 1985). Endogenous rhytms in mammals are coordinated by evolved in animals to enhance foraging efficiency as well as reducing risk of predated. Suprachiasmatic nuclei (SCN) with nerve cells in hypothalamus are responsible for coordination of endogenous rhythms in mammals. Endogenous rhythms are altered by light intensities which act indirectly on nervous system via retinal photoreceptor (Kramer and Birney 2001).

Orientation and disorientation as well as attraction and repulsion is one of the effect associated to light source. It will induce behavior such as territorial singing in nocturnal birds (Bergen and Abs 1997). Northern mockingbird (Mimus polygottos) males sing at night before mating, but it only mated once at night in area with artificial lights or during full moon (Derrickson 1988). Artificial luminance may disorient nocturnal animals to navigate in a dark environment. Hatching sea turtles moves away from low, dark silhouettes, which allow them to crawl quickly back to the ocean. Presence of beachfront lightning will results in disorientation which silhouettes that cued movement are no longer perceived. Lightning also affect the eggs-laying behavior of the female sea turtles (Salmon 2003).

Change in light level may interrupt orientation in nocturnal animals. Nocturnal animals have evolved to have higher and broader vision at night, and rapid increases in light may blind animals. In frogs, an increase in illumination causes reduction in visual capabilities which takes minutes to hours for it to recover (Buchanan 1993). Birds can also be disoriented and trapped within light zone which are unable to leave the lighted area. Large numbers of nocturnally migrating bird may collide each other and become exhausted and can be captured by other predators and hence interfering migrating route (Longcore and Rich 2004). The presence of light in night will also induces high amount of moth and other insect which are attracted to lights during the night. Nocturnal spiders are negatively phototaxis which attracts itself in respond to light (Nakamura and Yamashita 1997).

Artificial nocturnal lightings may also induce reproductive behaviors. A nocturnal female Physalaemus pustulosus frog are less selective about mate choice when light level are increased which prefer mate more quickly to avoid the increased predation risk of mating activity (Rand et al 1997). A recent laboratory study has been done by Wise S. in 2007 where melatonin production is lower in salamander which kept under lights. A more recent study by H. Savange et al has found that artificial illumination may delay metamorphosis on tadpoles which increases it’s mortality (Wise 2007). Buchanan (1993) found that frogs have stopped it mating activity during night football games when lights are emitted which leads to sky glow in the nearby stadium. The decrease of reproduction of frogs may inducing with greater danger for the species such as extinction. De Molenaar et al. (2000) investigate the relationship between lights and choice of nest site by observing the effect of roadway lightning on black tailed godwits (Limosa limosa) which was later found out that density of nest was lower up to 250-300m away from illumination. Thus result has concluded that illumination has an effect on population density of black-tailed godwits. Another experiment has been done by Wise and Buchanan which have found that artificial night lightning induces reduces in start term reduction in activity of salamander, which could limits the foraging activity and reduces growth and reproductive output, as well as survival rates during winter hibernation (Wise 2007).

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Light pollution can interfere with the interaction within a group of species which has previously maintained resource partitioning according to the illumination gradients. Most nocturnal mammals react to increasing light level by reducing their activity and restricting foraging (Beier P., 2006). Nocturnal squirrel tree-frog (Hyla squirrela) has the ability to forage in low lightning level (10-5 lux) under natural condition but avoid foraging if the illumination is over 10-3 lux (Buchanan 1998). Hailman (1984) also found similar effect on western toad (Bufo boreas) forages only at 10-1 to 10-5 lux where tailed frog (Ascaphus eruei) only forages below 10-5 lux. A study has been done on light intensity association with the activity patterns of nocturnal Patagonian leaf-eared mice (Phyllotis xanthopygus) which show that activity has been decreased during the 8 hour span when light intensity has increased (Kramer and Berny 2001). Clarke (1983) has shown the reduction relationship between high light intensity and the activity of nocturnal deer-mice (Peromyscus maniculatus) as an anti-predation response. All experiment has found evidence that artificial night lighting with similar intensity with moonlight reduces night activity and movement especially for animals which hides itself to prevent predation during night foraging. Although small nocturnal rodent are able to shift foraging activities, but larger rodents such as Hystrix indica have to abandon their light-phobic behaviors associates with increasing the predation risk in higher light levels (Alkon and Saltz 1988). Another study by Bird et al (2004) proves that lights discourages foraging activity where nocturnal beach mouse (Peromyscus polionotus) which foraging activity was significantly higher in dark arrays than light arrays.

Artificial illumination also disrupts the prey-predator relationship. Increasing in light levels will enhance benefits on predators where nocturnal animals will become more vulnerable and danger to prey. Nocturnal harbor seals (Phoca vitulina) has higher ability on prey on food which they gathered under artificial lights to prey on juvenile salmonids and reduced lights level also reducing in predation levels (Yurk and Trites 2000). Svensson and Rydell (1998) also found that mercury vapor lights which function as moth traps interfere with bat defense of nocturnal tympanates moths (Operophetera spp) by interfering with moth detection of ultrasonic chirps use by bats in echolation.

There is also an increasing problem of mortality of nocturnal mammals by road kill. Reed and Woodward (1981) found that increasing lightning on streets are not able to reduce road kill by vehicles. This is because nocturnal species are using the only rod system and bright light filled in retinas that nocturnal animals are difficult in avoiding collision with rapid increase of illumination. Some nocturnal species use lights to establish communication within each species and therefore it can be affected by light pollution. Bender et al (1996) found that coyotes (Canis latrans) group howling and group yip-howling are relatively related to increasing moonlight, where howling is a part of communication in coyotes. Since coyotes fully rely on light levels for visual cues in hunting and navigation, therefore ambient light levels may affect the behavioral patterns in coyotes (Bender et al 1996).

The presence of light pollution has demonstrated negative impact on the population ecology in the whole balanced ecosystem. Increasing in light intensity has caused behavioral problem such as orientation and disorientation and attracted in response to brightness. This has also creates danger in increasing risk of predation for nocturnal mammals where predators has higher chance for finding prey in the night and induces reduction of foraging activity on nocturnal animals. The major relationship between light pollution and nocturnal animals still required further research and design experiment to reduce mortality rate and risk of extinction on certain nocturnal species. Government should impose legislation law to reduce light emission among the countries especially in developed and developing country.

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