You'd be amazed at how often species disappear from habitat set aside for them but remain on privately owned property. National Parks really screwed up, for example, by planting sport fish to attract tourists - while many private land owners, including ranches, did not do such things and thus still have native rana species.
I am a biologist. I am not shocked by that at all. I am aware that national parks stock fish, and those fish screw up the local ecosystem. I even know some of the mechanisms by which they do it (for example: Introduced trout in the mountains of CA not only eat frog tadpoles directly, but are also preyed upon by Thamnophis atratus. This severs the dependency of the snakes on frogs, but because they still prey on the frogs their increased population sizes put additional pressure on frog populations already imperilled by agrocultural pollution and the direct effects of introduced trout)

It all depends on what the rancher is doing. Even heavily used cattle ponds on a ranch with thousands of cattle are suitable for some highly adaptable species (not most of your native frogs by the way, but a lot of toads. Some native rana can live there, but their populations are unstable and they are particularly vulnerable to bullfrog competition/predation in those ponds, as their tadpoles cannot compete with said bullfrogs for food in the microhabitats available in such ponds). Large scale prive cattle ranches (as opposed to state trust land) to my knowledge tend to completely destroy the habitat of all but the most resilient of amphibians (Like woodhouses toads, you might get some snakes that take advantage of rodents though...), and pretty much everything else for that matter. Moreover it does so over entire water sheds due to runoff from cow feces and subsequent eutrophication.

However if we are talking about a large tract of "ranches" (by which I mean rich people with horses or a large property they use as a private hunting preserve) the actual ecosystem changes are minimal, and this can represent a significant amount of protected land with minimal roads or human traffic.

You are shifting goal posts, arguing initially that agriculture is less damaging than urbanization to various organisms, then citing as an example something that is not agriculture.

Nothing was said about completely unregulated farming.
I just reread the original statement, I misread it and apologize.

Much of the water shortage currently going on is artificial, caused by a small minnow in the Delta. Seems they sometimes get killed in the pumps, so they turned the pumps off.

Our politicians are too stupid to figure out the unemployment costs are likely higher than the cost of a captive breeding program to supplement the wild minnow population.
I am not talking about the minnow (and did read the sensationalist article you reference). The farmers of the central valley (and indeed all of CA) dont just get their water locally (and they do...), but they import water from other states. Namely, Arizona and Nevada via the Colorado River Basin. Agriculture makes up the vast majority of the water use in the state. As the population grows throughout the region water gets pulled from reservoirs like lake meade and lake powell. The Colorado River no longer reaches the ocean, and the rate at which water is being removed from the reservoirs is not sustainable (the southwest has been in drought conditions for a decade) and is growing. Water prices are artificially kept low, and thus there is no check on demand.

This can largely be solved by cutting off the farmers from growing crops they have no business growing. Ex. Thou Shalt Not Grow Cotton In the Desert. It took the ESA being invoked to protect a fish being killed in the water pumps to get this done, because local politicians are more about their short term careers than the long term survival of their state.

And dont even get me started agricultural runoff from the central valley eutrophicating the ocean, and sex reversing frogs. Atrazine is not your friend.
When people starve, you end up with revolution. War does a lot of damage.
We already produce more than enough food (in western countries) to feed the worlds already inflated population. You propose a false dilemma. We have famine and hunger in places like central Africa because of systemic local problems (poor infrastructure, corruption, and poverty), oh and capitalism (Africa: the ultimate capitalist paradise, where people cannot buy food literally starve in the gutter)

I suspect, btw, that you'll find most ecological damage actually comes from lawns and pesticides used to keep lawns green aphids off the roses.
Farmers use science for the application of their fertilizers and pesticides, often they are required to by law but it also is cheaper for them. Use too much and the cost of excess hurts their bottom line, it is worthwhile for them to do frequent soil samples, etc.[/quote]
It all depends on what pesticide you refer to, and where you sample. If you look at reports of pesticide use done by the USGS, it is very clear that both urban and agricultural areas dump pesticides into watersheds. However they are different pesticides, and many many more agricultural samples were taken than urban samples. Looking at the distribution maps, you can see that most of the heavily polluted (measured as concentrations of a pesticide that breech a toxicological benchmark for wildlife health) urban streams are in major metro areas (New York, Chicago, Dallas etc). There were not many such areas sampled, but the ones that were were very bad.

The agricultural streams sampled that meet the same criteria, while they are a lower percentage, are the ones that run through large tracts of continuous agricultural land such as the Midwest and SE US, but not so much in agricultural regions in Montana, which are more scattered) . There were many many more of these sampled. What this basically means is that the net-effect of agriculture is higher, but so is the variation between sites. However the variation between urban sites was lower.
Moreover, when dangerous levels of pesticides are measured in animals tissues, a higher percentage of agricultural watersheds are heavily affected. Additionally, when human benchmarks are measured fewer urban streams were dangerous to people, but the groundwater was more contaminated. This suggests that the damage done remains local.
Moreover, urban areas don’t fertilize their streets and create nitrogen runoff…

Joe Six Pac does not use science, his runoff probably does more damage.
The USGS says otherwise.
We do need to change the way we farm and go more organic, but keep in mind, the less pesticides used the lower the crop yield, thus more land needs to be turned into farmland to feed the population.
Organic farms actually still use pesticides… they just don’t use synthetic ones. They use things like sprayed BT, and they introduce non-native bio-control agents. Their reliance on manure is also problematic as any science that gets done by conventional farms to balance soil nutrition cannot be done with ungulate feces, creating more runoff. That is in addition to the massive increase in land clearances.
What needs to be done is a switch to GM crops that resist drought and insects in order to maintain the same crop yield, relocate where we grow certain crops (read: thou shalt not grow crops with high water needs in the desert), place massive excise taxes on meat to decrease demand (because every kg of meat requires 8 kgs of vegatation) , and we need to institute population control to curve population growth (as it stands, we will reach the point were the planet cannot sustain our population in 40 years) . I would propose a cap and trade system on children…

Just clearing more land is shortsighted will not actually solve any problems.