Reduction in Gene Flow: Dietary Preferences

Speciation takes place when groups that were part of one species become reproductively isolated from each other.  Once the groups have become reproductively isolated from one another, speciation may result from each population becoming more and more adapted to their local environment (natural selection).  The gradual accumulation of random genetic mutations (a process known as drift) can also contribute to speciation, but at a much slower rate.   In the classic model of speciation, the process was only complete when no gene flow occurred between the divergent groups at all.  However, more recent research has shown that species can maintain their distinctness even when small numbers of hybridizations occur.

One way for two groups to become reproductively isolated from one another is by developing different dietary preferences.  This can happen when groups specialize on different parts of a resource (large versus small seeds, or insects that live on the outer tips of tree branches versus inner foliage near the trunk).  This results in individuals of different groups encountering one another only rarely simply because they are foraging in different habitats or different parts of the same habitat.  Diet-driven habitat isolation is different from the patterns of spatial separation I covered in my last post because it is not an geographical accident or some inherent physiological tolerance that is separating members of the two groups.

Dietary preferences can arise by mutation or in response to competition.  Favorable mutations may allow one group to utilize a whole new type of food which opens new habitats for that group to evolve into.  Such dietary innovations can lead to the evolution of different morphological features that further aid in the use the new resource.  These different morphologies can in turn lead to further reproductive isolation, and this process can become a self-reinforcing cycle.  This cycle is also supported by hybrids frequently having morphologies that are intermediate between the two groups.  These intermediate morphologies will likely be inferior to either of the groups and will result in hybrids leaving fewer, or no, offspring.  Natural selection will then favor adaptations to avoid hybrid matings because these matings will be wasted reproductive effort.  Competition can lead to differing dietary preferences by favoring the individuals in a population that are best suited to utilizing the extremes of a resource.  This can occur when competition for food resources is high.  Then if one group is able to utilize one end of a continuum and another group is able to utilize the other end, these populations may become favored because they avoid much of the competition.  Again, hybrids may do poorly because of intermediate morphologies that have evolved in response to the extreme ends of the food continuum, and also because they may have to deal with stronger competition from the other group.

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Reduction in Gene Flow: Spatiotemporal

Speciation takes place when groups that were part of one species become reproductively isolated from each other.  Once the groups have become reproductively isolated from one another, speciation may result from each population becoming more and more adapted to their local environment (natural selection).  The gradual accumulation of random genetic mutations (a process known as drift) can also contribute to speciation, but at a much slower rate.   In the classic model of speciation, the process was only complete when no gene flow occurred between the divergent groups at all.  However, more recent research has shown that species can maintain their distinctness even when small numbers of hybridizations occur.

Three major spatial patterns are commonly discussed when talking about speciation.  They are allopatric distributions, parapatric distributions, and sympatric distributions.

Allopatry (in ancient Greek allos means other and patri means fatherland) is when the two diverging groups live in different geographic locations which are separated by some geographic barrier such as a large body of water or a desert.  The barrier has to be large enough to stop animals from crossing it for allopatric speciaiton to occur.  In this situation, the barrier itself is what reduces gene flow between the populations.

Parapatric speciation (in ancient Greek para means beside and patri means fatherland) is when two groups are found in different parts of a continuous habitat with ranges that overlap only along a relatively narrow contact zone.  Their different ranges result in low levels of contact between members of the different groups, but there is no physical barrier stopping individuals from mixing.  Here, the different ranges play a partial role in reducing gene flow between the groups, but this alone would not be enough to allow speciation to take place.  In parapatric speciation, some other barrier must be reducing gene flow between the groups.  These barriers may be behavioral such as if the two groups preferring to feed or breed on different species that themselves do no overlap, or if the two groups develop different mating signals which the other group does not respond to.

Sympatric speciation (in ancient Greek sym means together and patri means fatherland) is when two groups become reproductively isolated while occupying the same geographic area at the same time.  In this mode of speciation, there is absolutely no geographic barriers to gene flow.  This means that any barriers to gene flow must have at least some behavioral component.  These behavioral differences much be significant if they are to prevent members of the two groups from interbreeding since the two groups live in very close proximity to one another.

Temporal patterns of speciation generally have to do with dispersal or migratory behaviors.

If two groups of a species migrate to different locations to breed, or if the chose mates during the non-breeding season and these non-breeding sites are in different locations, then this might be a form of allopatric speciation.  Here reproductively significant activities (selection of mates) take place in part of the year when the members of the different groups are in different locations.  Individuals would then choose a mate from those available which would be limited to other individuals who migrated to the same location, and so gene flow between the groups is prevented.  Different migratory patterns could be when one group is resident in a particular range and the other is migratory, or when one group migrates along a north and south pathway and another migrates along an east and west pathway, or when one group is an altitudinal migrant which moves up and down slope.  Gene flow can also be prevented if hybrids between members of the different groups display some behavior that results in high mortality.  For example, if one group is resident and the other migratory, a hybrid might have only a weak tendency to migrate and so not go vary far.  The area that they end up in might be very unsuitable to spend the non-breeding season in, and so these hybrids may have much higher mortality rates than purebred individuals.  This hybrid inviability would result in reduced gene flow between the groups.  Dispersal behavior can have a similar effect on gene flow.  If members of different groups have different dispersal tendencies (direction or distance), then intermediate dispersal behaviors may not be advantageous and so result in hybrid inviability as well.

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Effects of Fire and Species Distributions

Introduction

Fire plays and has played a unique and varied role in shaping ecosystems and the geography of species.   Fire has been a factor for all of Earth’s 4 billion years of existence, and all life has evolved in its presence (Stott 1988).  Its effects on species can be varied.  At high intensities, it has the ability to completely destroy total assemblages of species, yet there are many species that are unable to reproduce without it.  At lower levels of heat and exposure, fire can hold back ecological succession and maintain biological diversity.  This extensive timeframe and wide range of potential impacts makes fire an important, and sometimes critical, ecosystem engineer.  Yet little work has been done to explore the large scale biogeographic effects of fire.

Fire and the History of Life

For most of Earth’s history fires were ignited by lightning strikes and burned until they ran out of fuel or were extinguished by rainfall.  These ignitions occurred with a certain stochastic regularity in frequency and intensity for a given place and during given timeframes.  Forest managers call the particular combination of frequency and intensity the fire regime of a region.  Ecosystems had to evolve with the fire regime of that particular region as one of the abiotic factors alongside amount and seasonality of precipitation, temperature ranges, and soil chemistry.  Species that were not able to tolerate a particular fire regime were excluded from regions which burned in that manner.  Others evolved ways of protecting themselves from relatively infrequent fires and so could withstand the regime of that area.  Yet others evolved in areas that burn so regularly that the organisms became dependent on fire during parts of their life cycle.  And all these processes continue today.

Throughout the history of earth fire has also effected the composition of climactic zones.  It was found on Mount Kenya that the fire regimes have changed cyclically during the Pleistocene (Rucina et al. 2009).   Zones of climatic conditions moved up and down the slope as glacial periods came and went; this would lead us to expect species assemblages to move altitudinally according to their climactic needs.  However, this is not the case.  While some general movements can be attributed to climate, there are others in each cycle that cannot.  With each glacial-interglacial cycle the individual species which makeup each assemblage changed.  They move beyond the climatic region they had occupied before in ways that would not have been predicted.  The factor that best explains these differences is the patterns of fire left by layers of charcoal in the soil.  With the different cycles of glaciation, the fire regime changed and so the different species were shuffled into different assemblages.  These unique combinations of species resulted in different pressures from predators, prey, and competitors.  Such biotic shuffling opened up many new niches for natural selection to fill.  This shuffling has been demonstrated in modern times.  Sara et al. (2006) found that after a fire burned through an area it greatly disrupted the co-occurrence of many vertebrates, and changed the assemblage of species in stochastic ways.

The different fire regimes coming and going during the Pleistocene could have acted as a “species pump” with relic areas of a particular fire regime being separated and left behind as refugia as the climate and large scale fire regime of the region changed.  Populations within these relic fire regimes could then have diverged and even speciated before the preexisting fire regime and related conditions returned, bringing the new and ancestral populations back into contact.

Local Fire Ecology

For many species fire can have important and beneficial effects.   In some areas regular relatively low intensity fires have been shown to encourage forest expansion by thinning juvenile trees and thereby reducing competition for resources (Grau and Veblen 2000).   Openings in forests created by small scale fires have been shown to make habitat that is necessary for species that require disturbed areas (Askins et al. 2007).  Fire can also maintain certain habitat types that are high in biodiversity (Cox and Jones 2009).  Fire also plays an important role in certain stages of the reproduction of numerous species.  Lodgepole Pine (Pinus contorta ) has cones that are sealed closed and will open and release seeds only after being burned.  The seeds of Point Reyes Ceanothus (Ceanothus gloriosus) will only germinate after being exposed to a heat pulse such as that from a low intensity fire.

Fires maintain heterogeneous landscapes with different stages of succession that offer different habitat types.  This fragmentation commonly results in archipelagos of one habitat type isolated from one another by a different habitat type (Trabaud and Prodon 1993).   This has been found to increase the biodiversity in some habitats such as Hemlock-Hardwood forests in the eastern United States by increasing the number of habitat types in some areas (Ziegler 2000).  However, it has also been found to decrease biodiversity in others due to local population extinctions because of the isolation of habitat patches just as in island biogeography (Sara et al. 2006).  In other areas fire has been shown to hold back forest expansion and thereby maintain grasslands and the species that rely on them (Silva et al. 2001).

The beneficial effects of a fire can be especially far reaching if the species that directly benefits is a keystone species such as the Saw Palmetto (Serenoa repens) which provides food or habitat for several hundred species from a wide array of taxa.  Fire has been experimentally demonstrated to increase the number of flowers and the amount of fruit produced by Saw Palmetto in pine flatwoods in Florida (Carrington and Mullahey 2006).  In this way, fire applied at the proper frequency during the appropriate season, can influence the geography of an ecosystem by influencing not only the distribution of certain species, but the trophic systems as well.  It can even determine an ecosystems existence.

However not all fire is beneficial fire.  Major stand replacing fires remove vegetative cover and organic detritus completely exposing the bare mineral soil to erosion by wind and rain and to the desiccation by the sun. This can retard many ecosystems from expanding.  In extreme cases such high intensity fires can even prevent recolonization (Lomolino et al. 2006).  Fire in French oak forests has been shown to kill oak seedlings and so reduce recruitment rates (Curt et al. 2009).  The Bush Karoo Rat (Otomys unisulcatus) of southern Africa builds large nests of sticks that are very vulnerable to burning therefore its range is limited to areas that have very low fire frequency (Kerley and Erasmus 1992).  Shrubsteppe habitat contains another assemblage of species that is harmed by fire because after a burn the shubsteppe tends to be replaced by grassland (Earnst et al. 2009).  The openings and forest fragmentation that results from fire leads to increased edge effects which frequently include higher rates of predation, invasion of new species, and altered microclimatic conditions all of which can reduce biodiversity and cause local population extinctions.

Large Scale Fire Effects

These effects on assemblages of species and distribution of habitat types, both positive and negative, can be extended to the global scale.  An abiotic force that has such extensive influence on individual species has equally extensive influence on the distribution of biomes as a whole.  Fire has been shaping the distribution of biomes for millions of years, and around the world, a large area burns regularly.  Fire dependant ecosystems have evolved in these areas, and now comprise a large part of it and contain a huge number of species.  Species that would be reduced in number or go extinct in the absence of fire.

Biodiversity is increased in regions with fire.  Beaty and Taylor (2001) and Ziegler (2000) showed that areas of forest that experienced frequent fires had higher diversity of tree species than areas in which fires had been excluded.  This is another aspect that has larger biogeographic effects when the whole community is considered.  By increasing the number of tree species, the diversity of seeds and cones available as food sources increases and so does the number of species that use them, and these effects continue throughout the trophic levels of the area.

Ecological secession is also held back at a huge scale when examined globally.  It is estimated that there are many grasslands that occupy climatic regions and have nutrient levels that would support forests, and that the primary force preventing forests from spreading into these grasslands is the occurrence of frequent fires that kill tree seedlings and allow the grasses to maintain their presence (Stott 1988).  Bond et al. (2005) predicted that if fire were completely suppressed the global area covered by forest would double and that occupied by grasslands would be halved.  Such strong effects have equally dramatic results.  The more contiguous a habitat is on a global scale, whether grassland or forest, the greater the amount of dispersal and mixing species will be within it.  Further, fire is frequently the primary mode of decomposition and nutrient cycling in these grassland ecosystems (DeBano et al. 1998).  Frequent fires, and the resulting high rate of nutrient turnover, are critical for these habitats to maintain their high levels of productivity.  Such extensive influence makes fire an abiotic force comparable to precipitation or temperature in the determination of community biogeography.

Fire can also influence evolution and extinction.  Theoretically, the trait of flammability could evolve if fire spread from a flammable individual to kill neighboring individuals and if the seeds of the more flammable plant could out compete the seeds of less the flammable plants (Bond and Midgley 2003).  There is strong phylogentic support for the association of pines that lack self pruning, the loss of dead lower branches, and cone serotiny (Schwilk and Ackerly 2001).  This association makes sense.  Serotinouse pines have a strong incentive to expose their cones to fire, so the individuals that retained fuel material on their trunks that would allow fire into the tree crown would produce more offspring than individuals which had to rely on high intensity crown fires to occur naturally.

Even within species, fire plays a role in natural selection.  In grasslands that burn frequently, saplings of the African tree Acacia karroo grow straight up which quickly takes the foliage above the level of the low surface fires which are common in that habitat.  However, in areas which burn only rarely A. karroo saplings form tangled cage-like structures.  This serves as an example of the selection pressures exerted by fire (Archibald and Bond 2003).

Fire and Native Peoples

Native peoples used landscape fire in a variety of ways as a tool to control habitat for their own gain.  Evidence for hominid use of fire dates back 1.4 million years (Gowlett et al. 1981).  Intermittent, low intensity fire was used by Aboriginal peoples in Australia to clear ground and replace nutrients in the soil for agriculture (Yibarbuk et al. 2001).  They also used fire around their dwelling places to clear away vegetation and allow for better visibility of their surroundings.  It is thought that this allowed them to see large movements of prey, and also to prevent enemies for approaching unnoticed.  Kershaw (1986) showed that dramatic increases in microscopic charcoal in core samples matched the receding of Araucaria forests and the replacement with Eucalyptus forests in north eastern Australia.  Differences in the transition between forest types and climatic conditions in the cores indicate that landscape fires set by colonizing Aboriginals are most likely source of these fires and the resulting habitat changes.  They also appear to be responsible for the extinction of at least one tree species, the rainforest conifer Dacrydium (Bowman 1998).  Aboriginal landscape fire is certainly responsible for the maintenance of a mosaic of fire intolerant rainforest and fire tolerant Eucalyptus forests during the Pleistocene (Clark 1983).

Native Americans used fire in several ways.  Native Californians set brush fires to drive game, such as rabbits, into waiting entrapments for easy capture, and seed meadows were routinely burned to increase yields in future years (Margolin 1978).  In so doing, native tribes affected the distribution of species.  They facilitated the presence and spread of fire tolerant species at the expense of species less fire tolerant.  They also altered habitat structure which resulted in more “park like” habitat.  This influenced which species persisted and which were excluded.

However, in more recent times fire has been viewed by humans as a force of destruction only and has been suppressed almost completely in many parts of the world.   This has lead to an increase in the amount of fuel material and a corresponding increase in the intensity of the fires when they do inevitably break out.  The suppression of fire has also lead ecosystems to change in ways that they had been otherwise prevented from, reversing the effects the native peoples and natural fire regimes had had on the landscape.  We are still not at all sure what the full consequences of these changes are.

Conclusions

Whether fire is used as a management tool, suppressed completely, or ignored all together there will be a corresponding effect on biogeography, and these biogeographic effects cannot be underestimated.  As forests expand or contract whole assemblages of species are shifted.  If the fire in a given location increases fragmentation, there will be a corresponding increase in edge effects and the disturbances that go along with them.  Such disturbances can ultimately lead certain species to local or total extinction.  However, other ecosystems have evolved to incorporate fire as an integral feature.  Whatever the effects are, their impact will be extensive and reach throughout the ecosystem.  All these effects compound when the global scale is considered.

Cited Literature

Archibald, S. and W. J. Bond. 2003. Growing tall vs. growing wide: tree architecture and allometry of Acacia karroo in forest, savanna, and arid environments. Oikos. 102: 3-14.

Askins, R. A., B. Zuckberg, and L. Novak. 2007. Do the size and landscape context of forest openings influence the abundance and breeding success of shrubland songbirds in New England? Forest Ecology and Management 250: 137-147.

Beaty, R. M.  and A. H. Taylor. 2001. Spatial and temporal variation of fire regimes in a mixed conifer forest landscape, Southern Cascades, California, U.S.A. Journal of Biogeography. 28: 955-966.

Bond, W. J., and J. J. MIdgley. 1995. Kill thy neighbor: an individualistic argument for the evolution of flammability. Oikos. 73: 79-85.

Bond, W. J., F. I. Woodward, and J. J. Midgley. 2005. The global distribution of ecosystems in a world without fire. New Phytologist. 165: 525-538.

Bowman, D. M. J. S. 1998. The impact of Aboriginal landscape burning on the Australian biota. New Phytologist. 140: 385-410.

Carrinton, M. E. and J. J. Mullahey. 2006. Effects of burning season and frequency on saw palmetto (Serenoa repens) flowering and fruiting. Forest Ecology and Management. 230: 69-78.

Clark, R. L. 1983. Pollen and charcoal evidence for the effects of Aboriginal burning on the vegetation of Australia. Archaeology in Oceania. 18: 32-37.

Cox, J. A., and C. D. Jones. 2009. Influence of prescribed fire on winter abundance of Bachman’s Sparrow. Wilson Journal of Ornithology. 121(2): 359-365.

Curt, T., W. Adra, and L. Borgniet. 2009. Fire-driven oak regeneration in French Mediterranian ecosystems. Forest Ecology and Management. 258: 2127-2135.

DeBano, L. F., D. G. Neary, and P. F. Ffolliot. 1998. Fire effects on ecosystems. John Wiley & Sons, Inc. New York, New York, U.S.A.

Earnst, S. L., H. L. Newsome, W. L. LaFramboise, and N. LaFramboise. 2009. Avian Response to wildfire in interior Columbia Basin shrubsteppe. Condor 111:370-376.

Gowlett, J. A. J., Hairns, J. W. K., Walton, D. A. and Wood, B. A. 1981 Early archaeological sites, hominid remains and traces of fire from Chesowanja, Kenya. Nature 294: 125-9.

Grau, H. R. and T. T. Veblen. 2000.  Rainfall variability, fire and vegetation dynamics in neotropical montane ecosystems in north-western Argentina. Journal of Biogeography. 27: 1107-1121.

Kerley, G. I. H. and T. Erasmus. 1992. Fire and the range limits of the bush Karoo rat Otomys unisulcatus. Global Ecology and Biogeography Letters. 2: 11-15.

Kershaw, A. P. 1986. Climatic change and Aboriginal burning in north-east Australia during the last two glacial/interglacial cycles. Nature. 322: 47-49.

Lomolino, M. V., B. R. Riddle, and J. H. Brown. 2006. Biogeography 3^rd edition. Sinauer Associates Inc. Sunderland, Massachusetts, U.S.A.

Margolin, M. 1978. The Ohlone Way: Indian life in the San Francisco-Monterey bay area. Heyday Books. Berkeley, California, U.S.A.

Rucina, S. M., V. M. Muiruri, R. N. Kinyanjui, K. McGuiness, and R. Marchant. 2009. Late Quaternary vegetation and fire dynamics on Mount Kenya. Palaeogeography, Palaeoclimatology, Palaeoecology. 283: 1-14.

Sara, M., E. Bellia, and A. Milazzo. 2006. Fire disturbance disrupts co-occurrence patterns of terrestrial vertebrates in Mediterranean woodlands. Journal of Biogeography. 33: 843-852.

Schwilk, D. W. and D. D. Ackerly. 2001. Flammability and serotiny as strategies: correlated evolution in pines. Oikos. 94: 326-336.

Silva, J. F., A. Zambrano, and M. R. Farinas. 2001. Increase in the woody component of seasonal savannahs under different fire regimes in Calabozo, Venezuela. Journal of Biogeography. 28: 977-983.

Stott, P. 1988. The forest as Phoenix: towards a biogeography of fire in south east Asia. The Geographical Journal. 154(3): 337-350.

Trabaud, L. and R. Prodon. 1993. Fire in Mediterranean ecosystems. Ecosystem Research Report No. 5. Commission on European Communities, Bussels.

Yibarbuk, D., P. J. Whitehead, J. Russell-Smith, D. Jackson, C. Godjuwa, A. Fisher, P. Cooke, D Choquenor, and D. M. J. S. Bowman. 2001. Fire ecology and Aboriginal land management in ventral Arnhem Land, Northern Australia: a tradition of ecosystem management. Journal of Biogeography. 28: 325-343.

Ziegler, S. S. 2000. A comparison of the structural characteristics between old-growth and postfire second-growth hemlock-hardwood forests in Adirondack Park, New York, U.S.A.  Global Ecology and Biogeography. 9: 373-389.

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Codornices Creek Watershed

Codornices Creek runs from the hills of Berkeley, California where its headwaters feed from the little valleys and ravines of Grizzly Peak Ridge.  From there it flows down out of the hills, through several city parks, and then down through much of urban Berkeley all the way to the San Francisco Bay where it has its terminus just north of the Golden Gate Fields racetrack.  The whole watershed drains about 1504 acers (Figure 1) which results in from three to thirteen cubic feet per second of water to flow out of the mouth of Codornices Creek each year.

 

Let’s take a walk through this watershed, a walk that will move through space an time.  What happened along the banks of this creek, and what is happening now?  Who and what lived in and used this watershed, and who and what is living here and using it today?

The Ohlone Indians arrived in the area sometime before 500 C.E., and lived along this creek.  In the upper areas of the watershed, they hunted deer, rabbit, and squirrel.  They also collected the nuts of Bay Laurel trees and acorns for food.  Later, the Spanish, and even later Mexicans, granted the whole area as part of the Rancho San Antonio.  It remained a rancho until Americans stole or bought the land after gold was discovered in California.  Today, deer still live in the hills around the headwaters, as do rabbit and squirrel, although the species of squirrel had changed from the native Western Grey Squirrel to the invasive Eastern Fox Squirrel.  Both Bay Laurels and Oaks are still producing their seeds.  However, more has changed than the species of squirrel.  Several non-native plants have been introduced that are quite different from anything the Ohlone would have lived with.  Eucalyptus trees, Scotch Broom, and English Ivy all now are making impacts on the native habitat.  Further, many animals that the Ohlone might have encountered are gone.  The Mountain Lion could still be found in the watershed, but in far smaller numbers than historically would have been here, and the Grizzly Bear used to roam through this area in large numbers, but does so no longer.

At the bottom of this area of mostly untrammeled habitat, the creek enters several city parks.  These are almost a transitional zone between the open space of the watershed above and the suburban and urban areas below.  These parks have left the creek alone.  They have worked with or around the water for the most part.  Codornices Creek Park is where the headwaters all join to become the unified Codornices Creek that flows the rest of the way.

One section in this stretch of watershed that is not owned by the city is owned by the Beth El Temple.  On this land the creek has undergone quite a bit of change.  When Beth El purchased the land, neighbors were concerned for future of the creek, and as part of the sales settlement the temple was required to develop a plan that would limit damage to the creek during construction.  However, during construction, a significant amount of sediment was released into the creek.  To prevent further sediment releases, and to lessen the impact that the construction was having on the banks of the creek, Beth El decided to move the entire creek bed.  They re-dug a stream channel, diverted the flow, and then began to replant the new banks with native vegetation.  All of this at considerable cost, no doubt.

Once the creek flows into more urban areas of Berkeley, it begins passing through a series of daylighted sections and culverts.  Most of the way to the bay the creek is daylighted.  It is culverted only where it passes under a cross-street making it the most open creek in the east bay. Most of the path of the creek is on private property and, between streets, there is still quite a bit of vegetation on the banks as the creek runs between houses and through yards.  However, even though the creek is open to the sky along for most of its length, that does not mean that it is in is natural state now.  This entire region of Berkeley used to be the flood plain of Codornices Creek.  Now, retaining walls that alter and redirect the flow of water, concrete creek bottoms that reduce available habitat, and limited room for the creek bed to meander have all changed the hydrology of Codornices Creek substantially from when the Ohlone and Spanish would have seen it.  All these changes cause the creek to flow faster now than in times past.  Faster flow means more incising of the bed, more erosion, and more debris carried by the water.  Further the creek is completely culverted when it passes directly under Martin Luther King Jr. Junior High School.

While there are no large open areas where smaller tributary streams can flow into Codornices Creek in such an urban environment, this does not mean that the creek has no water flowing into it from this area.  The city streets are still part of the watershed, and the runoff from them carries pollutants, both chemical and solid, with it into the creek.

At the lower end of the watershed, the creek passes under the railway track, where it is open, and under I-580, where it runs through a culvert.  From there it then flows out into a small marsh next to the Golden Gate Racetrack.  Down along this section of creek, the Ohlone used to catch Steelhead Trout, and some of these fish can still be found in the lower section of the creek.  Then, finally, Codornices Creek comes to it’s terminus at the bayshore where it flows into a tidal mud-flat.

These fish, along with frogs and other amphibians, many birds and several mammals are all reminders that there is still wilderness in Codornices Creek, and it needs support and protection.  This work is being done by local non-profit organizations such as the Friends of Five Creeks and the Urban Creek Counsel.  These groups have worked to restore habitat and water quality along the creek and are continuing to monitor many aspects of the effects that humans are having on the Codornices Creek watershed.

 

References:

– The Codornices Creek Watershed Restoration Action Plan (2003).  From the Live

– Oak/Codornices Creek Neighborhood Association.  Available at http://loccna.katz.com/creek/ActionPlan-Kier.html

– FrogWatch USA (2003). From the National Wildlife Federation.  Available at

http://www.nwf.org/frogwatchusa/display.cfm?showState=ca&showSite=135

– Live Oak to Tamalpais Walk (1998).  From the Berkeley Path Wanderers Association.  Available

at http://www.berkeleypaths.com/walkhandouts/walk_LiveOakToTamalpais.htm

 

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